Tuesday, April 30, 2013

Vojvodina: Serbia's Last Yugoslav Legacy

The North Caucasus, a favorite topic of both my Twitter addiction and my spotty record as a blogger, has jumped from back-page obscurity to an American national obsession thanks to the Chechen heritage of the two Boston Marathon bombing suspects. Naturally, I now pay a visit to this long-neglected blog to write about...someplace else.

Even before the bombing, the Caucasus was already a popular topic among security, human rights, and foreign policy geeks thanks to its violent recent history, the geopolitics of Russian oil and gas pipelines, and a growing list of awkward questions about next year's Olympic Games in Sochi. But fifteen hundred miles due west of Chechnya is someplace else with no vital resources and no history of warfare since the Second World War, leaving it even more unfamiliar among a general American audience than the Caucasus was until April of 2013. Several different dramas have held the world's attention over the last few weeks, including Boston, Syria, North Korea, and even West, Texas. While almost no one was looking, an unexploded bomb left over from the Yugoslav Wars may have begun to tick in the geographic center of Europe.

Now that the other five ex-Yugoslav republics—Slovenia, Croatia, Macedonia, Bosnia-Hercegovina, and Montenegro—and one of Serbia' two autonomous provinces, Kosovo, are all independent countries, Serbia's last inheritance from the Yugoslav era is its other autonomous province, Vojvodina (voy-VOH-dee-nuh). With nearly two million people on a chunk of real estate comparable in size to Massachusetts or El Salvador, Vojvodina accounts for almost exactly a quarter of both the land and the people of Serbia. Sitting one hundred miles north of Kosovo at the confluence of the Danube, Tisa, and Sava rivers, its table-top plains are a verdant Central European contrast to the hills and valleys of the Serbian heartland and the windy Balkan highlands of Kosovo. Vojvodina is mostly farmland and is often described as Serbia's breadbasket, but it also includes the northern suburbs of Belgrade, Serbia's capital. Vojvodina's own capital and largest city, the Danube port of Novi Sad, is also Serbia's second-largest city.

Before briefly explaining its history and demography, it must first be said that the crisis unfolding in Vojvodina today is rooted in the conflicting agendas of rival political parties and, in no small part, the competing egos of their leaders. If ethnic diversity is a certain guarantee of trouble in the Balkans, then surely Vojvodina would have been among the first places to explode in the early Nineties. Instead, when the regime of Serbian leader Slobodan Milošević neutered Vojvodina's autonomy in September of 1990, the reaction was far more hostile in places as far afield as Slovenia and Croatia than in Vojvodina itself.

That said, Yugoslavia was destroyed by political opportunists like Serbia's Milošević and his Croatian counterpart Franjo Tuđman who showed no scruples about exploiting the worst impulses of local bigotries to fill the political void left by the breakdown of communism. By ending the autonomy of Kosovo and Vojvodina, Milosevic firmed up his control over Serbia at the cost (deemed acceptable to him) of driving the other Yugoslav republics to abandon the federation. To use a phrase with heavy portent in Central Europe, the same thing could happen again two decades later.

Vojvodina is a surviving relic of the dazzling diversity that was once typical of Central Europe. Whole communities like the local Germans and Jews were swept away by twentieth-century catastrophes, but Vojvodina is still far more diverse than the rest of Serbia. Ethnic Serbs account for almost exactly two-thirds of its population, compared to a solid nine-tenths majority in the Serbian heartland. Ethnic Hungarians form the next largest group at about 13%, mostly clustered in the far north of the province along the Hungarian border around Vojvodina's second-largest city, Subotica. The last one-fifth of Vojvodina's people are a kaleidoscope of different Central and East European communities, with Slovaks, Croats, Roma (the people once better known as Gypsies in the West), Romanians, and Montenegrins each accounting for at least one or two percent of the population apiece, plus more than a dozen other communities accounting for a least a few hundred people each. These smaller categories include familiar nationalities like Ukrainians, Macedonians, and Albanians but also stateless groups like the Bunjevci (a Roman Catholic South Slav people speaking yet another dialect of Serbo-Croatian), the Rusyn (an Eastern Catholic people whose East Slav language is similar to Russian and Ukrainian), and the Gorani (Bulgarian-speaking Muslims). Even the more familiar groups are often marked in Vojvodina by local distinctions; Slovakia itself is a devoutly Roman Catholic country, but the fifty thousand Slovaks who make up 2.6% of Vojvodina's people are mostly Evangelical Protestants whose ancestors left their homeland in the eighteenth and nineteenth centuries in search of both prosperity and religious freedom. Modern Vojvodina has a total of six official languages: Serbian, Hungarian, Slovak, Romanian, Croatian, and Rusyn.

It is only fair that such a diverse people should have a long and complicated history. This land belonged to the Hungarian nation for most of the last thousand years, but its people have always been a mix of languages, religions, and identities. Serbs have lived here since the Middle Ages and became dominant after a huge influx of Serb refugees fleeing Ottoman Turkish rule further south in the late 1600s. Over the next century, as the Ottoman Empire peaked and then decayed, these northern Serbian lands straddling what is now Croatia, Bosnia and Serbia itself became a broad military frontier between the predominantly Roman Catholic empire of Austria to the north and the Muslim-dominated empire of the Ottomans in the south. This sense of being the front line of European Christendom in an eternal war against Asiatic Islam became an ingrained central theme in the Serbian national identity and endures to this day, notwithstanding the awkward fact that their modern neighbors (in both the national and personal senses) include millions of people who are simultaneously Europeans and Muslims.

Hungarian rule lingered here even after the Serbian heartland won its independence from the Ottomans in gradual stages over the 1800s. By then, Hungary was a core territory of the vast and multicultural Austrian Empire, and a Hungarian revolt in 1848-49 was crushed thanks in part to the loyalty of Serb subjects whose anxiety over the prospects of direct rule by an independent Hungary trumped any resentment of comparatively remote Austrian rule. The result was an orgy of fighting between Hungarians and Serbs, including hideous crimes against civilian noncombatants on both sides. The entire city of Novi Sad was destroyed in the uprising, and virtually none of its modern buildings predate 1848 even though the city itself was founded exactly one hundred years earlier (its original Austrian name was Ratzenstadt, "Serb City" in German). The uprising's legacy still casts a shadow over relations between the two peoples almost two centuries later. Austria rewarded southern Hungary's Serbs for their loyalty by creating a new autonomous region called the Serbian Duchy or, in Serbian, Srpska Vojvodina.

It took less than twenty years for Hungary to seize another chance to defy Austria. In 1867 (the same year that the last Turkish troops left Serbia after five centuries of occupation), Austria suffered a crushing defeat in the series of wars that birthed modern Germany. Hungary forced the Austrians to preserve their tottering empire at the cost of transforming it into a new nation: the dual monarchy of Austria-Hungary. Having fought so long and so valiantly for its own self-rule under Austrian domination, Hungary in the late nineteenth century turned full circle and adopted one of the most repressive and nationalistic of all European regimes of its time. Now an equal partner in the empire it had once resisted, the government of Hungary crushed any expression of distinct identity among the Slovaks, Croats, Romanians, Serbs, and other non-Hungarians who comprised half of its people. This would become part of a toxic legacy that exploded half a century later in the First World War, destroying both the old European order in general and the sprawling Kingdom of Hungary in particular.

The entire map of Central and Eastern Europe was rebooted at the end of the First World War as empires on both sides buckled under the weight of four years of war on top of their own internal flaws and collapsed, Hungary among them. The eastern half of Vojvodina briefly joined a neighboring Austro-Hungarian province to form the Banat Republic, but this entity basically existed only on paper for a few weeks in November of 1918 before it was invaded and carved up by two of the war's victorious allies, Serbia and Romania. To the south, Serbia itself became the core of a new Kingdom of the Serbs, Croats, and Slovenes, soon renamed as "the land of the South Slavs", Yugoslavia. A Serb-backed anti-Hungarian regime in Vojvodina announced its intent to join the new nation in December of 1918, and the allies formally endorsed the new state of affairs the following year.

All of the defeated Central Powers suffered painful terms of surrender at the Paris Peace Talks in 1919, most infamous today for the treaty imposed upon Germany at Versailles, but the losses for Germany in both land and people were far smaller on a per capita basis compared to what Hungary lost in the Treaty of Trianon. Two-thirds of its land and its people were awarded to neighboring countries, leaving behind only a shrunken core of the Hungarian heartland around the capital city Budapest. Inevitably, politics in both Hungary and Germany fell victim to the curse of irredentism, the desire of defeated nations to reverse history and redraw their national boundaries to return lost territories and perhaps even gain new lands from their enemies as compensation. The Nazis exploited German irredentism to deadly effect, but undoing Trianon became a kind of national religion in Hungary during the Twenties and Thirties. As Germany under the Nazis rearmed and demanded a reversal of the First World War's consequences, few other nations supported Hitler's foreign policy with greater enthusiasm than Hungary's own dictator, Admiral Miklos Horthy (in stark contrast to Horthy's resistance to the Final Solution on the domestic front). All of Hungary's neighbors had benefited from Trianon, and most of the lost territories had large local ethnic Hungarian minorities and even local majorities in places like northern Vojvodina. All such regions became lightning rods for Hungarian irredentism, which pushed the country into a suicidal alliance with Nazi Germany.

Vojvodina endured two consecutive genocidal catastrophes in the 1940s. The original Yugoslavia, the Serb-led kingdom created after the First World War, was attacked and destroyed in 1941 by Nazi Germany and its fascist partners. Most of Vojvodina was partitioned between Hungary and Croatia during the Second World War, with only the southeastern part left under the jurisdiction of the German-occupied remnant of Serbia. It is estimated that the fascist occupation from 1941 to 1944 killed fifty thousand of Vojvodina's people, including almost all of its Jewish residents and thousands of Serbs and Roma. Many of these people were killed at Jasenovac in Croatia, the only Auschwitz-style fascist extermination camp not under direct German administration. The end of the war and the defeat of fascism brought a new wave of violence as the new communist regime attacked its own enemies. An estimated 200,000 people from one of Vojvodina's largest and oldest ethnic communities, the local Germans, were exiled to Germany, while more than forty thousand others were sent to prison camps where thousands died of abuse or neglect. The communists also killed tens of thousands of Serbs, Hungarians, and others in Vojvodina deemed hostile to the new regime.

Vojvodina's modern boundaries were set at the end of the Second World War when the communists under Marshal Tito created the second version of Yugoslavia, a communist federation of six republics and two provinces, but its specific legal status has changed several times since then. The province was originally under almost total control by the republic of Serbia, but a new Yugoslav constitution in 1974 made Vojvodina comparable to a republic, complete with a veto in the unwieldy collegiate presidency that ruled communist Yugoslavia during its final stage. When Milosevic ended this autonomy and imposed total Serbian control in 1990, Vojvodina itself accepted the change with little resistance even as the rest of Yugoslavia reacted with fear, rage, and a renewed determination to seek independence.

Vojvodina escaped the worst of the violence in the early 90s, but local Croats became targets of suspicion and prejudice during Croatia's war of independence from Yugoslavia and the subsequent war of secession by Croatia's own Serb-majority regions. As many as ten thousand Vojvodina Croats fled the province during 1992, mostly from villages in the southwest near the Croatian border. The most infamous incident involved the ethnically mixed village of Hrtkovci where a campaign of harassment was led by Vojislav Šešelj, leader of both Serbia's ultranationalist Radical Party and the Chetnik paramilitary squads who committed atrocities against Croatian and Bosnian civilians during the Yugoslav Wars. Bloodshed was minimal, including one confirmed murder, but more than seven hundred Croats left Hrtkovci under the immediate threat of deadly violence, leaving their homes to be occupied by Serb refugees from other parts of Yugoslavia. Even so, their were conspicuous incidents of bravery in which ethnic Serbs risked their lives defending Croat neighbors, and some of the instigators were later imprisoned (including Šešelj himself, who is now on trial for war crimes).

The fall of the Milošević regime in 2000 began Serbia's slow but inexorable transformation into a multi-party democracy governed by rule of law, and part of this process was the gradual return of Vojvodina's lost autonomy. Its current political structure dates to a 2008 reform that created a local chief executive, the Government of Vojvodina, led by a President and four Vice-Presidents, along with a single-chamber local legislature, the Assembly, headed by the President of the Assembly (usually referred to simply as Speaker as in most other parliamentary systems). The political landscape in Vojvodina today is a mix of parties with national profiles across all of Serbia—the center-left Democrats (DS), the rightist Progressives (SPS), the ultranationalist Radicals (SRS), and others—and smaller regional parties, many of them ethnic-specific like the Alliance of Vojvodina Hungarians (SVM).

May of 2012 saw Vojvodina's second parliamentary vote since the current structures were created in 2008. A bloc of centrist pro-EU parties led by DS lost the Serbian national elections but took first place in Vojvodina and formed the new government in coalition with a regional party, the League of Social Democrats of Vojvodina (LSV). Their chief rivals, an SPS-led center-right coalition, won the national election but came in second place in Vojvodina. The result was a mirror-image of the election results in Serbia as a whole, where SPS leader Tomislav Nikolić took office as President of Serbia while DS second-in-command Bojan Pajtić became President of the Government of Vojvodina. The highest ranking non-Serb in local politics is Speaker István Pásztor from the SVM.

The current political crisis has been building for weeks and began, as such things often do, with a dispute over money. In March of 2013, police arrested three former officials from a local bank on suspicion of pocketing twenty-five million euros of the bank's money. A few weeks later in early April, this regional bank was seized by a national Serbian bank. What could have been a mere jurisdictional squabble automatically became more politicized simply because the provincial and national governments were controlled by each other's arch-rivals.

But one thing kept this from becoming a headline-dominating crisis in itself: Serbia was already completely engrossed in its internal debate over the Western-backed agreement on mutual recognition between Serbia and Kosovo. Very briefly, Serbia remains committed to joining the European Union and otherwise becoming a "normal" European democracy, but the EU has made it clear that any progress on Serbia's part is preconditioned on reaching a deal on normal diplomatic relations with Kosovo. That's fine, except that "normal diplomatic relations" pretty much carry the condition of recognizing Kosovo as an independent country, something that is still inconceivable to a large and vocal minority of Serbs. This situation was especially awkward for Serbia's President Nikolić, who had only just won the presidency in May of 2012 after defeating a DS incumbent who was lambasted by Nikolić's party as too soft on Kosovo and too willing to bend to EU pressure. Even so, a lengthy and often frustrating final series of negotiations began between the two states in October of 2012, starting with a groundbreaking meeting between both countries' prime ministers. After months of slow but steady progress, Nikolić announced on March 11, 2013, that a final deal was imminent.

Maybe Pajtić assumed that now, with everyone preoccupied with the Kosovo deal, the time was right to push back on the banking issue with a political move that might otherwise stir controversy. If this was his assumption, he may have miscalculated.

On April 6, Pajtić announced a "declaration on the protection of the constitutional and legal rights of Vojvodina." Pajtić's political rivals in the SNS cast the announcement as something close to a trial run at a declaration of independence from Serbia. Aleksandar Vučić, Serbia's Deputy Prime Minister and leader of Pajtić's rightist SNS rivals, said that his party respected the province's autonomy but would not allow "separatist games" and organized an April 12 anti-secession rally in Novi Sad. The rally was held under the slogan "Stop the breaking up of Serbia" and drew heavy support from the SNS and a smattering of other national and regional parties from across the political spectrum. Pajtić denied that he wanted Vojvodina to seek independence but accused national authorities of trying to bring down his government "at any price." Also, the SNS insists that the vast majority of the rally's roughly 30,000 participants were actual Vojvodina residents, while a senior DS member said that most were shipped in from other parts of Serbia. DS and its coalition partners in LSV made a joint statement on April 22 denying any "trace of separatism" in the declaration on Vojvodina's rights. So emotionally loaded is the situation that the SNS even pointed out that the announcement coincided with the infamous anniversary of the wartime Croatian fascist state's 1941 declaration of independence from the old royalist Yugoslavia.

No single incident related to the rally roused more attention than the appearance of graffiti in various parts of Novi Sad threatening death to Vučić and warning Serbs in general and the SNS in particular to leave Vojvodina. The graffiti was written in neither Serbian nor Hungarian but rather in Albanian, a language indigenous to fewer than 2,300 people in Vojvodina or about one-eighth of one percent of its population. This provoked accusations that the graffiti had been written not by Albanians or any other ethnic minority, but rather by Serb provocateurs in general and possibly by SNS supporters in particular.

For good or ill, the Kosovo deal continues to bleed tension away from Vojvodina. Serbia and Kosovo announced mutual support for the deal on April 19, and attention has since shifted the Herculean task of convincing tens of thousands of Serbs in autonomous North Kosovo to accept the deal, which includes allowing their territory to come under the rule of the Kosovar government in three stages. For their part, the North Kosovo Serbs insist that the deal be at least held to the minimum standard of a popular referendum, a position which the government in Belgrade describes as "pointless" given the certainty of its defeat.

One other point worth briefly mentioning is the political situation north of the border in Hungary itself. One of the first East Bloc countries to jettison communism in 1989, Hungary has ranked as a confident democracy and a well-developed market economy since early in the Nineties. But its high global standing has taken an unexpected jolt over the last three years under the leadership of current Prime Minister Viktor Orbán. This relatively young politician is already a veteran of Hungarian politics, having co-founded the Alliance of Young Democrats, known in Hungary by the abbreviation Fidesz, during the implosion of communism. Orbán remained broadly respected abroad for his role in the fall of communism through his first tenure as prime minister around the turn of the millennium and a subsequent decade spent in opposition. But even then he established a political image that The Economist described as a mix of "cynical populism and mystifyingly authoritarian socialist-style policies."

Orbán has been prime minister again since 2010 when a rightist coalition led by Fidesz won two-thirds of the Hungarian parliament, a supermajority giving them the ability to pass an entirely new national constitution which has already been amended four times. Domestic and foreign critics alike have accused Fidesz of undermining basic democratic institutions. Among other things, Hungary's Constitutional Court finds itself in the ironic position of no longer having the authority to examine and amend the national constitution. Any law backed by the current government is, for all practical purposes, impossible to block from passage. Other odd legislative flourishes under Orbán include a law limiting election campaigning to state media outlets only and restrictions that keep university students stuck in Hungary for a minimum of three years after graduation if they ever took state aid. The bulk of the criticism has focused on the fourth amendment, actually a fifteen-page bundle of multiple amendments that sweeps away restrictions on government power and promptly triggered alarms across Europe.

Orbán's populism is hardly at the fringe of Hungarian politics. That distinction belongs to the ultranationalist party Jobbik whose virulent antisemitism and open nostalgia for fascism have made them international pariahs, notwithstanding their current third-place rank in the Hungarian parliament. And transcending any left-right distinction is the long memory of the lands lost in the treaty of Trianon nearly a century ago. Even liberal politicians routinely voice their concerns over the large and potentially vulnerable Hungarian minorities in southern Slovakia, Romanian Transylvania, and of course in Vojvodina. Genuine or not, the anti-Serb graffiti incident from mid-April seems to have blown over, but it raises the possibility of even localized inter-ethnic violence in Vojvodina. If local Hungarians should come under threat, sympathy in Hungary will resonate far beyond the nationalist extreme right, and public opinion will obligate almost any government to respond. With any luck, such a response would be limited to diplomatic and humanitarian activity.

In closing, there is near-universal consensus among Balkan-watchers that two other regions in southern Serbia are far more likely to flare up as flashpoints than Vojvodina. Perhaps critically, neither of these regions has any political autonomy now or during the Yugoslav era. Due east of Kosovo in the Preševo Valley of southernmost Serbia are a handful of noncontiguous villages and towns with large ethnic Albanian communities. These waged their own intermittent but violent insurgency after the Kosovo War with the goal of joining a "Greater Kosovo" until 2001 when NATO and their own co-ethnics in Albania and Kosovo made it bluntly clear that any further changes to local borders were off-limits. Further west, the border between Serbia and Montenegro straddles the historic region of Sandžak whose people are a near-equal mix of ordinary Orthodox Christian Serbs and Muslim Bosniaks. Both of these regions are in particularly dire economic straits, and the chances of serious unrest in either is probably partially defused by the fact that young people are leaving the regions in droves in search of better opportunities elsewhere. None of this is true of Vojvodina which, while relatively poor, still has a stable population base.

Vojvodina, still far from a tipping point, is nonetheless worthy of more attention. With Hungary's government weathering a storm of foreign and domestic criticism, Serbia's government struggling to convince a heartsick country to accept its cherished national cradle as an independent country, and all of Europe seeing a disturbing resurgence of far-right nationalist parties like Golden Dawn in Greece and Svoboda in Ukraine, regional tension is nothing unusual in the broad sweep of Vojvodina's history. One conspicuous difference this time is that, unlike 1941 or 1991, the world's attention is already monopolized by other catastrophes far from Central Europe.

Wednesday, February 27, 2013

Asteroids: A (Fairly) Brief Overview


This computer-generated but completely realistic view of Vesta is compiled from thousands of actual images collected by NASA's Dawn probe during 2011 and 2012. The parallel groves are part of a system of deep fractures in the northern hemisphere, the Divalia Fossa, created by ancient impact events near Vesta's south pole that came close to shattering the asteroid. Each groove is over a mile deep and up to nine miles long.
Image Source: NASA/JPL

It’s only two months into 2013 as I write this, and already the year has been marked by watching the skies. Last year ended with predictions that Comet ISON will rank among the most spectacular in recorded history when it passes through the inner Solar System next autumn. The new year began with a slim but much-hyped risk of the asteroid Apophis hitting Earth. A month later, a second asteroid known only by a numeric designation was overshadowed on the day of its closest approach by the meteorite impact near Chelyabinsk, Siberia, whose passage through the sky caused a shock wave that shattered millions of windows and injured more than one thousand people. A space-themed post seems timely after neglecting this blog for several months, and few topics intrigue me so much as asteroids. As luck has it, few topics in astronomy are also more dogged by misinformation. For anyone with a few minutes to spare, I promise to answer some questions, clear up some popular misconceptions, and hopefully stir you to find more information...

First, A Quick Note on Distances
Anything related to space involves grappling with distances which seem colossal from a human perspective, but asteroids fall into a middle ground on the scale of the broader universe. On the one hand, even people with only a casual knowledge of science fact or science fiction are familiar with the light-year as the distance a beam of light travels in one year, about six trillion miles or ten trillion kilometers. Light-years are helpful for quantifying the mind-boggling spaces between separate stars, but using light-years to measure distances within the Solar System is like using miles to measure rooms or even shelf space inside just one house, leaving you with a decimal point followed by a conga line of zeroes. On the other hand, miles and kilometers still pile up into the millions and billions on this scale, leaving our eyes to glaze over again from counting zeroes.

Instead of miles or light years, the most popular yardstick for measuring distances within the same star system is the distance from Earth to the Sun. The name of this middle-ground astronomical unit is a triumph of utility over imagination: the Astronomical Unit or AU. Rounded for convenience, one AU is about 93 million miles or 150 million kilometers, not quite 400 times the distance between the Earth and the Moon. Going the other way, it would take 63,241 AU to equal one light-year (the preference for plurals is still to use AU instead of AUs). In terms of light speed, sunlight reaching Earth right now left the surface of the Sun eight minutes and nineteen seconds ago, and so one AU is equal to 499 light-seconds. Measuring our Solar System with this handy new yardstick leaves Mercury scorching at just 0.4 AU from the Sun, while distant Neptune sits in the cold and darkness at thirty AU from the Sun.

The imaginary world of scale models is always the best tool for grasping astronomical distances. By a convenient coincidence, the number of AU in one light-year almost matches the 63,360 inches in one mile, and so converting AU to inches reduces the Solar System to a scale model that mere humans can wrap our brains around with relative ease. Neptune’s orbit would be almost exactly five feet across on this scale, the fluff along the Solar System’s frontier extends almost a mile farther out, and the nearest star system beyond our own is four and one-third miles away. Before we get too comfortable with this scale, the center of our galaxy would still be about thirty thousand miles away (about one-seventh of the way to the Moon in reality) and the nearest like-sized galaxy in Andromeda would still be more than two million miles away. Once again we are reminded that the sheer size of even our cosmic backyard is, in the most literal sense, unimaginable.

As for measuring the main asteroid belt between the orbits of Mars and Jupiter, remember that a swarm of discrete objects has no clearly defined borders that can be marked off with the precision of, say, a country on a map. Still, for the sake of convenience, astronomers usually draw the belt’s inner boundary at about 2.06 AU from the Sun and the outer edge at about 3.27 AU. Those numbers sound so specific because they’re rooted in the concept of orbital resonance, a topic which requires a mercifully quick detour through the topic of orbital mechanics. Bear with me for a few moments as we step back from the asteroid belt and briefly detour to poor, lonely, neglected Pluto.

A Longer But Still Relatively Quick Note on Orbits
The nitpicky academic and bureaucratic side of astronomy got some public attention in 2006 when Pluto lost its status as a full planet. There were many reasons for the decision, but two of the most dramatic involve Pluto’s bizarre orbit. Pluto is far from the asteroid belt, but much of the current definition of what defines a planet was in response to the negative example of Pluto, and the issue directly affects the asteroid belt.

For starters, Pluto’s orbit is so far off from being perfectly round that it actually crosses the orbit of Neptune for twenty years out of its 248-year-long trip around the Sun. Having an orbit clear of any like-sized or larger objects is now one of the criteria for full planethood, and having a reasonably roundish orbit is a logical precondition to that. No planet has a truly round orbit, but none are as goofy as Pluto (yes, that one never gets old).

How much an orbit deviates from being perfectly round is called orbital eccentricity, and it’s expressed with a decimal value greater than zero and less than one. A value of one or higher is possible, but that means an object is not in an orbit, strictly speaking, but is merely whipping through our cosmic neighborhood on a one-time-only visit, as many comets do. Pluto beats all eight of the true planets with its orbital eccentricity of 0.25, meaning that its distance varies from its closest approach to the Sun (or perihelion in space-talk) of 29.66 AU to a maximum distance (or aphelion) of 48.87 AU from the Sun. Earth’s eccentricity of only 0.017 makes our orbit seem boringly round by comparison, varying only from a perihelion of 0.98 AU to an aphelion of 1.02 AU. It should be noted that eccentricity also wobbles over a timeframe of thousands of years, but by the time the values given here are out-of-date, no one alive in 2013 will care.

The other trait of Pluto’s orbit that annoyed astronomers is its high orbital inclination. If you imagine that the Sun and the eight planets could fit into a giant pizza pan, the planets’ orbits are all close enough to the same plane that our imaginary humungous pan would be quite shallow, relatively speaking. Seen from the Earth, the Sun moves through the sky against the fixed background of stars along an imaginary line called the ecliptic. The other planets all move through the sky along paths that are so close to the ecliptic that the average plane for all eight planets combined is only two degrees off from the ecliptic. The worst offender for both orbital eccentricity and orbital inclination is Mercury, with an eccentricity of 0.21 and an inclination of about seven degrees off the ecliptic, but Pluto beats Mercury on both counts. Add Pluto to our imaginary pizza pan, and it deepens to something more like the dimensions of a pie tray to accommodate Pluto’s whopping seventeen degree orbital inclination. On the upside, its heavy inclination is why Pluto never slams into Neptune when their orbits cross.

So how does all of this relate to the asteroid belt? Well, each asteroid has its own unique orbit, but the asteroid belt treated as a whole would actually make a fairly bland planet. Some rogue asteroids are wildly eccentric and cross planetary orbits between perihelion and aphelion, but those in the main belt have an average eccentricity of only 0.17, even less than Mercury. The vast majority of them are polite enough to mind their business between the orbits of Mars (about 1.52 AU from the Sun) and Jupiter (about 5.2 AU from the Sun).

Asteroids are less orderly when it comes to inclination but still not by too much. Almost all asteroids in the main belt are inclined by thirty degrees or less, which sounds drastic compared to the planets or even Pluto, but plenty of individual asteroids and especially comets are so deeply inclined that Pluto and the main-belt asteroids look boring and well-behaved by comparison. Factor in comets and the bizarre newly found objects beyond Neptune, and suddenly the whole Solar System looks more like a giant doughnut than anything as flat as a pizza or even a pie.

Gaps, Zones, and Resonance
We can step away from Pluto now, but we’re not quite done with orbital mechanics just yet, and the man responsible for that is a nineteenth-century American astronomer named Daniel Kirkwood who spent decades studying and tracking asteroid orbits. When studying an orbit, astronomers tend to focus on its semi-major axis, which is basically the object’s greatest possible distance from the center of its own orbit. That may sound like an obscure way of saying its distance from the Sun, but the two aren’t quite the same thing because the Sun is not the true center of an elliptical orbit (although they’re relatively close unless the asteroid is wildly eccentric, which is rarely true of main-belt asteroids).

Kirkwood discovered five conspicuous gaps in the main belt where almost no asteroid has its semi-major axis, plus several more subtle gaps where only a few asteroids have their semi-major axes. Asteroids can still cross these Kirkwood gaps in the course of their orbits, and the overall number of asteroids there at any given moment is about the same as anyplace else in the belt, so the existence of Kirkwood gaps only came to light through decades of patient observation and tracking. With freakishly few exceptions, any asteroid whose semi-major axis settles into a Kirkwood gap after a collision or some other effect of random chance soon gets nudged out of that position into a different, more stable orbit. If you think about an old vinyl record album, Kirkwood gaps are like the raised ridges between the album’s grooves; even if you deliberately try to drop the record needle onto a ridge, it just slips into a groove instead.

Kirkwood also found an important pattern about the location of these gaps, and this pattern hinges on the largest planet and outer neighbor of the main belt: Jupiter. The single most prominent Kirkwood gap happens to be at 2.5 AU from the Sun, and any object with a semi-major axis in that spot would orbit the Sun exactly three times for every time Jupiter orbits the Sun once. Saying the same thing more briefly, a semi-major axis at 2.5 AU has an orbital resonance of 3:1 (“three to one”) with Jupiter. Its tremendous mass and gravity make Jupiter act like a kind of shepherd for the main asteroid belt, and every Kirkwood gap has a nice, round, integer-based orbital resonance with Jupiter like 4:1 or 5:2, as opposed to a more arbitrary non-integer-based resonance like 3:2.5 or 4.25:2.

Source: Wikimedia Commons, based on data plotted by Alan Chamberlain of JPL/Caltech. Uploaded June of 2007, retrieved 23 February 2013.

The five main Kirkwood gaps offer guideposts both for drawing boundaries for the entire asteroid belt and for splitting it internally into zones. The very first Kirkwood gap at 2.06 AU from the Sun marks the semi-official “start” of the belt, although a few stragglers have semi-major axes dipping in as far as about 1.78 AU just past the aphelion of Mars (1.67 AU). Likewise, the last gap at about 3.27 AU marks the semi-official “end” of the belt, although even more asteroids taper off past the outer edge as far out as about 3.5 AU.

So far at least, there is no single convention for partitioning the asteroid belt like some kind of celestial Homestead Act. The simplest method is to split the belt into inner and outer zones along the most significant Kirkwood gap at 2.5 AU. A slightly more common method splits it into three zones: the first goes from the beginning out to the main 2.5 AU point, the second from there out to the 5:2 resonance gap at 2.82 AU, and the third from there out to the end. Note that an asteroid can still be regarded as part of the main belt even if it travels within or beyond the belt at some point in its orbit as long as its semi-major axis is within the belt, a situation which describes plenty of asteroids. Not surprisingly, both of the tiny Martian moons and dozens of Jupiter’s seventy-ish (and always rising) moons are almost certainly just wayward asteroids captured by each planet’s gravity in the distant past.

Talk of orbits and boundaries may seem like dull details, but it’s all an important set-up to one of the most basic, common, and at least potentially practical questions about asteroids.

Just How Many of These Things Are There?
Now and forever, the most accurate and literal answer is, “Too many to count.” At some point, there needs to be a minimum cut-off between a small asteroid and a mere speck of cosmic debris, but no such benchmark exists yet. It’s all reminiscent of the “What is a planet?” debate that was, arguably, laid to rest back in 2006. The word meteoroid is used with the general understanding that an asteroid is larger than a meteoroid, but again there is no fixed boundary between the two. (Just to clarify, a meteoroid becomes a meteor once it enters the atmosphere and glows, and any piece that reaches the ground intact is a meteorite.) But given the lack of a minimum accepted size for an asteroid, the literal number of asteroids is essentially infinite.

That answer satisfies few people, so we can parse the numbers for something less open-ended. More than two centuries of telescopes combing the main belt has reduced it to familiar turfr large objects and feeling like familiar turf to sky-gazers. Querying the NASA/JPL Minor Planet Database for main-belt asteroids measuring at least sixty miles or one hundred kilometers across known as of February 26, 2013, yields a total of 183 matching results, and it’s unlikely that many objects of that size or larger have gone undiscovered for so long in the main belt. (The Kuiper belt past the orbit of Neptune is a whole other matter, but that’s tremendously farther away than the main belt, which is our back yard by comparison; we will probably be finding Kuiper belt objects that size and larger for decades or even centuries to come.) Running the same query on the same day with the benchmark dropped to objects as small as only one kilometer across yields a total of 2,039 known objects, but there are credible academic guesstimates of more than one million asteroids in that size range that are still undiscovered. One NASA-endorsed figure for the total number of asteroids measuring at least 100 meters across is about 150 million. For some context, Arizona’s famous Barringer Crater was probably made by an object about fifty meters across.

Astronomers are confident enough with the data at hand to make broad physical assessments of the main belt. Early theories about the belt being rubble from a planet destroyed by some ancient catastrophe fell flat in the early 1900s. In plain language, there just isn’t enough stuff in the asteroid belt for that theory to work. Everything in the main belt combined makes an object with less than one-twentieth the mass of Earth’s own Moon. The largest object in the belt—Ceres, promoted from biggest asteroid to smallest dwarf planet in 2006—accounts for almost a third of the belt’s mass by itself. Add just the three largest asteroids to Ceres, and you already have half of the belt’s total mass right there.

Shedding Light on Asteroids
The popular Hollywood image of the asteroid belt as a cluttered and dangerous tumble of constantly colliding objects (think of that scene in Star Wars: The Empire Strikes Back) is pure fantasy. Anything launched from Earth and aimed at random in the general direction of the asteroid belt would probably hit nothing larger than dust. The best real-world version of the asteroid scene in Empire would be navigating Saturn’s main rings, and even there you’re limited to a vertical plane that’s only a few hundred feet deep, plus the obstacles are giant icebergs instead of giant boulders. Dramatic collisions of large asteroids only happen on a timeframe of thousands or even millions of years. In short, Threepio should stick to etiquette and protocol, because his math sucks.

As of early 2013, not one of the eleven space probes that have entered or crossed the asteroid belt even came close to hitting an asteroid by accident. Three never even came close enough to one for a decent picture, and remember that just landing intact on our next-door neighbor Mars has proven to be a coin-toss by comparison. All of this is good news for any mission bound for the outer reaches of the Solar System.

The bad news is, besides that handful of probes, we are stuck with studying asteroids from across cosmic distances. In practical terms, this mostly translates into a matter of studying the sunlight reflected from their surfaces. Spectroscopy is the analysis of fine lines hidden within the spectra, sunlight reflected off asteroids, to learn which chemical substances each asteroid is made of. As will be explained shortly, spectroscopy is a vital tool for sorting asteroids and categorizing them into similar groups.

Another important light-based trait is an asteroid’s albedo, the measurement of how reflective it is. A hypothetical surface with absolutely no reflectivity (perfectly black, in other words) has an albedo of zero, while another hypothetical surface that reflects absolutely all light (perfectly white) has an albedo of one. Naturally, real-world objects fall somewhere between these two. The single most reflective object known in the Solar System is an ice-covered moon of Saturn named Enceladus with an albedo of 0.99 (it basically looks like a world-sized white cue ball from a billiards table), but there are probably distant objects beyond Neptune in the Kuiper belt that will give Enceladus a run for its money once we discover them. By comparison, our own Moon has an albedo of only about 0.12, while the average albedo of Earth as seen from space is about 0.3 thanks mostly to cloud cover. Asteroids run the gamut from very low to very high albedos but overall tend to be low. It makes sense that albedo has a lot to do with whatever substance dominates the surface of each asteroid, whether it be a dark cinder-like substance or a more reflective substance with a higher mineral content.

Measuring traits like spectral lines and albedo may lack the rewarding substance of scooping up a handful of dust in our gloved hands, but these are the best we can do until something or someone actually pays a visit, and these still tell us a great deal about asteroids even across such awesome distances. Only a few of the biggest asteroids are likely to have complex, layered internal structures similar to planets; Ceres, Pallas, Vesta, and Hygiea are the only main-belt objects at least 250 miles across and even approximately round. The vast majority are small enough to be more-or-less homogenous lumps of loose material adrift in space. Recent probe data on the masses of some asteroids supports an early guess that many are not even solid bodies in the strictest sense; instead they are swarms of discrete objects barely held together by their own weak mutual gravitational pull, the illusion of a solid appearance created by a surface layer of silt and dust. If such an object miraculously appeared at rest in the full one-gee gravity of Earth’s surface, it would collapse pathetically into an enormous gravel heap with maybe a few boulders inside. In a fit of practicality, astronomers refer to such bodies by the straightforward name of rubble-piles.

That Goofy Question Again: What Is a Planet?
Having covered some generalities about where asteroids are, how they move, and roughly how many of them exist, it’s time to meet some actual asteroids. Even in the remote telescopic sense, this only started happening in the early 1800s, but our understanding of them has grown by leaps and bounds given such relatively little time. Even so, we still struggle with not only a lot of unanswered questions but also with many self-imposed headaches stemming from a lack of universal standards and definitions.

When asteroids were first discovered, they were given respected names from Roman mythology just like ordinary planets. First up was Ceres, discovered by Giovanni Piazzi on New Years Day of 1801 and named for the Roman goddess of grains who inspired the English word “cereal.” Next came Pallas, discovered in the summer of 1802 and named for the great Greek goddess Athena, whose many alternate names included this Roman moniker. Up next was Juno in 1804, named for Jupiter’s wife, and then Vesta in 1807, named for the virgin goddess of home life and namesake of ancient Rome’s famous Vestal Virgin priestesses.

And then an entire generation passed passed with no new discoveries. In the meantime, mainstream scientific opinion saw these four as otherwise ordinary planets remarkable only for their small sizes and for sharing oddly similar orbits. Textbooks from the early 1800s routinely listed the planets as: Mercury, Venus, Earth, Mars, Ceres, Pallas, Juno, Vesta, Jupiter, Saturn, and Uranus.

But there were skeptics even in the beginning, and none matched the fame and authority of living legend William Herschel, the brilliant German-born British man of many talents who became the first person in recorded history to discover a planet (Uranus) in 1781. Herschel recognized early on that these four micro-worlds were something different and, in 1802, coined the new word asteroid. The name literally means “star-like” because asteroids were still mere flickering pinpoints of light even when observed through the best telescopes of his time, whereas planets grew into Moon-like discs with features and details even through fairly modest telescopes. But Herschel was ahead of the curve, and his new word sat neglected in the ivory tower of science for half a century while the outside world regarded these four oddballs as full-fledged planets.

After thirty-eight years, the dry spell broke in 1845 with the discovery of Astraea, named for a minor goddess connected to both justice and the stars, Such an obscure name was a hint of things to come, because new objects were being soon discovered between Mars and Jupiter so quickly that it became obvious that granting full planetary status to all of them was unworkable and inappropriate. Herschel’s half-forgotten asteroid label finally took off in the 1850s thanks mostly to the endorsement of a respected Prussian astronomer named Alexander von Humboldt, the man who probably coined the name “asteroid belt.”

The limited roster of names in Roman mythology buckled under the numeric challenge ahead, especially given a semi-official preference in these early days for only female names. The tally of asteroids had just passed the one hundred mark in 1868 when the situation got completely out of hand in the 1870s with the rise of astrophotography. Now, instead of straining their eyes through sleepless nights staring through a telescope in person, astronomers merely had to study photographic plates the next morning and watch for changes in the same corner of the sky from night to night. The late 1800s was a golden age for cataloging all kinds of celestial objects as telescopes, cameras, and astrophotography techniques kept improving. Even as the pace of asteroid discovery grew, it was still early enough that leaving any unnamed seemed inappropriate by the naïve standards of the day.

Bending the Rules
By the time the asteroid tally passed one thousand in 1921, the early preference for feminine names from Roman mythology was already in tatters. Even as early as 1852, the twentieth asteroid was given a Roman name with a non-mythological source: Massalia, the ancient name for the French city of Marseilles (many asteroids and comets were discovered from a great nineteenth-century observatory at Marseilles). Five years later, the forty-fifth asteroid dropped the classical world altogether and was named Eugenia for the empress of France at the time. Even astronomer Alexander von Humboldt got an asteroid named in his honor in 1858, although its name was still feminized to Alexandria. In 1862, the seventy-seventh asteroid was named Frigga in honor of a goddess, but Norse instead of Roman. Two years later came the eightieth asteroid was named in honor of a real woman from Antiquity, Sappho, the famous poet and icon of lesbian love. Asteroid eighty-nine was named for St. Julia the martyr of Corsica, while asteroid 140 honored the pagan Slavic goddess Siwa. Asteroid names were still disproportionately feminine or ancient as the twentieth century began, but 1894 saw the first complete break from any trace of the old guidelines of feminine, ancient, or both with the naming of asteroid number 334, Chicago.

Classical mythology still casts a long shadow thanks to some early precedents. In 1898, an asteroid was discovered whose perihelion was inside the orbit of Mars but otherwise spent most of its orbit in the main belt. It was named Eros, the Roman form of the Greek Cupid, and a convention was established that eccentric “Mars-crossers” should be named for mythological males. Another one of my essays already covered the concept of trojans, asteroids located outside of the main belt in zones of gravitational stability along the orbits of the planets, and Jupiter’s trojans are all named in honor of the great Greek and Trojan heroes from Homer’s epic stories of the Trojan War like Hector, Achilles, and Odysseus. Even farther away, asteroids beyond the orbit of Saturn out as far as Neptune are known as centaurs, and these are all named for specific members of that mythical race of human-horse hybrids. Famous centaurs from both mythology and astronomy include noble Chiron, tutor of many mythical heroes who was immortalized in the sky as the constellation Sagittarius the Archer, and the doomed couple of brave Cyllarus and beautiful Hylonome, the latter ending in suicide after her lover was killed in battle against humans.

But these exceptions only add to the problem because whole categories of names must be set aside for the exclusive use of trojans, centaurs, and other oddballs, diminishing the list of available names for the main belt. It was evident that something had to give, and so a new system was launched in 1925. Like so many twentieth century innovations, this one was a triumph of bureaucracy and numbers.

Numbers Before Names
The agency in charge of asteroid names is the International Astronomical Union or IAU, the same body which hosted the debate over defining a planet in 2006 that ended with Pluto’s demotion. The specific duty of tallying and tracking minor planets—that’s asteroids, dwarf planets, Kuiper belt objects, centaurs, trojans, and a few other niche categories—falls to the IAU’s Minor Planet Center at the Smithsonian Astrophysical Observatory in Cambridge.

(As a brief aside, the term “minor planet” was technically one-upped in that same 2006 IAU meeting that defined planethood at Pluto’s expense. The IAU now prefers that a new term be used to describe any object in the Solar System that is not a planet, a dwarf planet, or a moon, a definition broad enough to cover everything in the asteroid belt except for the dwarf planet Ceres. Unfortunately, the new term is an unwieldy mouthful: small Solar System body or SSSB. The IAU recommends usage of SSSB but stopped short of killing off the older term “minor planet,” which has the twin advantages of brevity and covering the dwarf planet category too. Between this and the continued existence and importance of the MPC, only “minor planet” is used here. Chalk me up as anti-SSSB.)

When a new minor planet is found, the MPC gives it a humble provisional designation. These are a far cry from lofty old classical names like “Prosperina” and “Melponeme.” Instead, they look like “1997 DB15” or “2012 BX109.” The opening number is obviously the year of discovery, but the rest needs a little crib sheet. Fortunately the system is fairly straightforward even if it includes on quirk that annoys some numbers-purists.

The first letter after the year shows the specific half-month of its discovery. The letters I and Z are skipped to make an even two dozen half-months, and every month is split between the fifteenth and sixteenth days no matter how many days are in that month. For example, objects found in the first fifteen days of January get an A, objects found in late January get a B, objects found in early February get a C, and so on all the way down to objects found on or after December 16, which get a Y.

The second letter tells the sequence of each object’s discovery within that half-month. For instance, the first object found in early January of 2013 would be 2013 AA, the second would be 2013 AB, and so on. Z is available for the second letter, but I is still skipped to avoid visual confusion with the numeral 1.

Speaking of numerals, the pace of asteroid discovery was slow enough in the early 1900s for just two letters to cover all contingencies, but those days are long gone. With more telescopes on the ground and in space than anyone in 1913 could have imagined, minor planets are now being found and cataloged at a pace of thousands per month thanks mostly to automated asteroid-hunting programs. Once twenty-five objects are found in the first half of January, then the next object after 2013 AZ (remember, no letter I) becomes 2013 AA1, the next is 2013 AB1, then 2013 AC1, and so on until you get to the fifty-first object, 2013 AA2. This syntax annoys some numbers purists because the number at the end takes precedence over the letter before it, but a sequence of letter-number-letter like a chemical formula was apparently deemed unsightly. Speaking of chemical formulas, that final number in a provisional designation is technically supposed to be a subscript like the little 2 in H20, but rendering subscripts is still a headache for so many hardware and software packages (including Blogger) that it is usually written as an ordinary numeral.

Provisional designations can endure for years or decades, but eventually an asteroid is observed enough times by enough different astronomers for its orbit to be plotted and any accidental duplicate observations to be straightened out. At this point, the Minor Planet Center passes the baton to the next body in the IAU custody chain, the Committee for Small Body Nomenclature. The CSBN then gives the asteroid a full-fledged permanent designation, a number assigned in sequential order of discovery.

A typical example of a permanent designation comes from a relatively famous asteroid found during the summer I was born. This otherwise unremarkable lump of rock about thirteen miles across took the provisional designation of 1971 QX1 until the CSBN gave it its permanent designation: 2309. (It’s amazing how a mere four-digit number already looks downright quaint in this modern age of six-digit designations, not to mention how old it makes me feel.) In other words, the asteroid formerly known as 1971 QX1 became object number 2309 on the IAU’s register of cataloged asteroids, thus making its permanent designation (2309) 1971 QX1. We’ll come back to this one in just a bit and explain why it attracted some attention.

Even the old, long-named minor planets now have retroactive permanent designations. The original four from the early 1800s are now properly called 1 Ceres, 2 Pallas, 3 Juno, and 4 Vesta. Notice that the parentheses around the permanent designation can be dropped for named asteroids, though it’s preferable to keep them for unnamed asteroids to avoid all those numbers from blurring together. The number may be dropped in casual speech and just the name used, but always remember that the permanent designation is a vital part of each asteroid’s complete identification regardless of whether or not it has a name.

The latest data on asteroids is freely available courtesy of a specific NASA website, the Jet Propulsion Laboratory’s Small-Body Database. If you ever use spreadsheets, then you will have no trouble generating all kinds of nifty tables with the most up-to-date numbers for specific minor planet categories. [EDIT: It would help if my hyperlink to the database survived the copy-paste process, sorry — DJT 2/28/13.] JPL-SBD data will be used later when discussing asteroid categories, but bear in mind that all JPL-SBD data cited from here on was retrieved on February 26, 2013, and thus will be out-of-date by the time I finish typing this sentence, much less by the time someone else reads it.

Pet Peeves
Dropping that dull provisional designation altogether and replacing it with a normal (relatively speaking) name is the privilege of each asteroid’s discoverer. Submitted names become official with the monthly publication of the Minor Planet Circular. The MPC reserves the right to veto names, but guidelines are fairly lax. Naming an asteroid for yourself is forbidden, but this is easily bypassed when astronomer buddies name asteroids for each other, which happens a lot. Naming an asteroid for someone only famous as a businessperson is frowned upon as a kind of “buying your way into the heavens,” but this can also be ignored if the person was a philanthropist, hence 742 Edisona (note the quaint nineteenth-century feminized name). Honoring a political or military figure now has a mandatory delay of one hundred years after that person’s death, but plenty of people squeaked by before the rule was set (U.S. President Herbert Hoover somehow sneaked in twice with 932 Hooveria and 1363 Herberta). Spaces and punctuation marks were once discouraged and are still less common than simply running names together like 5892 Milesdavis and 17744 Jodiefoster, but even relatively old ones like 3043 San Diego and 3552 Don Quixote bent the rule.

It’s impossible to exaggerate the quantitative impact of current automated asteroid-hunting programs that reduce human effort to little more than opening a spreadsheet. The IMU limits each astronomer to naming no more than two asteroids every two months, a deliberate logjam which leaves the vast majority of asteroids numbered but unnamed. The tally of asteroids with permanent designations passed the five digit mark in 1982 and six digits in October of 2005, but the number with proper names still languishes down in the low five figures. As of February of 2013, Wikipedia cites data retrieved in September 2010 giving the lowest-numbered unnamed minor planet as (3708) 1974 FV1, but some asteroids with six-figure numbers already have names too. Fittingly, one of the newest names in the January 2013 Minor Planet Circular is the former (274301) 2008 QH24, now called 274301 Wikipedia.

One other naming guideline is enforced with some controversy, all thanks to the asteroid that I already mentioned as being notorious in astronomical circles. Asteroid (2309) 1971 QX1 was discovered on August 16, 1971 by American astronomer James Gibson. Years later, Gibson and his wife Ursula collaborated on picking a name when 2309 became eligible and ultimately settled on 2309 Mr. Spock. Simply naming an asteroid after a mere Star Trek character probably still seemed frivolous enough once upon a time, but the asteroid’s specific namesake was actually Gibson’s gray tabby. Apparently the MPC was less irritated by naming an asteroid for a fictional Vulcan than for a real cat, and so an announcement was made that asteroids should not be named for pets.

What makes the controversy seem illogical is that Mr. Spock was not even the first asteroid named after a pet. One of the greatest names in observational astronomy is that of Germany’s Max Wolf, an early powerhouse in the field of astrophotography whose catalogs of comets, stars, asteroids, and other celestial bodies were among the most thorough of his time. His good-natured rivalry with American counterpart and close friend E. E. Barnard was a driving force in late nineteenth- and early twentieth-century observational astronomy, not to mention his early advocacy of the modern planetarium as an instrument for stirring popular interest in the sky. (Wolf even has his own tenuous Star Trek connection too; one of the Solar System’s nearest neighbors is a dim star less than eight light years away tallied on his star catalog as Wolf 359, which became the fictional setting of a crucial battle in the Star Trek universe.) By the time he died in 1932, Wolf personally discovered a then-record-setting 248 asteroids, including two found in March of 1902 which he named 482 Petrina and 483 Seppina. The names are feminized tributes to his dogs Petrus and Sepp, the latter a nickname derived from Joseph and hence the German equivalent of “Joey.”

From “1 Ceres” to “12818 Tomhanks” in Just Two Centuries
The roster of asteroid names runs from the solemn to the absurd, but it oversimplifies things to say that early asteroid names were all lofty classical references and modern asteroids are all named for old sweethearts or rock stars, with some arbitrary cutoff point around the time of Woodstock. Still, astronomers tend to be a whimsical bunch by scientific standards, and a disproportionate number are gifted amateurs with no academic pretensions.

An early practical detour away from classical references was when nineteenth-century astronomers showed gratitude by naming discoveries for financial sponsors. Max Wolf named his very first asteroid 323 Brucia in honor of a wealthy New York patron of astronomy named Catherine Wolfe Bruce whose donation of $10,000 built Wolf’s powerful telescope in Heidelberg. (For ten grand in 1887 dollars, an asteroid is probably the least the lady deserved. Sure enough, she is also the namesake of a small but conspicuous crater located at almost the exact center of the Moon’s near hemisphere, so that the Earth is always directly overhead at Bruce Crater.) Wolf also named two other asteroids for American philanthropists: 1038 Tuckia for Edward Tuck and 904 Rockefelia after John D. Rockefeller. Likewise, the great Austrian-Czech astronomer Johann Palisa named one of his more important discoveries 719 Albert in honor of the Vienna Observatory’s recently deceased patron, Albert Salomon von Rothschild (this was the second Mars-crosser after 433 Eros).

Despite the international spirit of astronomy, patriotism made early appearances in names chosen for celestial bodies, the most glaring example being William Herschel’s original wish to name the planet Uranus after England’s King George III. The roster of asteroids offers no shortage of examples: 712 Boliviana (honoring South American liberator Simon Bolivar), 852 Wladilena (a once trendy Soviet name honoring Vladimir Lenin), 1841 Masaryk (for Czechoslovakia’s first president), 2351 O’Higgins (honoring Chilean founder Bernardo O’Higgins), and of course 886 Washingtonia. Even the original dozen asteroids were rounded out with 12 Victoria, officially named for the Roman goddess of victory but also a thinly veiled tribute to Britain’s Queen Victoria.

Even modern asteroid names are not all fun and frivolity. The first human in space is immortalized through 1772 Gagarin, while the Apollo 11 crew are the namesakes of 6469 Armstrong, 6470 Aldrin, and 6471 Collins. The long list of astronauts, cosmonauts, and recent Chinese taikonauts conspicuously includes the crew of the lost space shuttles Challenger (numbers 3350 through 3356) and Columbia (51823 through 51829). Turning away from space exploration, not only is 5305 Annefrank on the list, but so is one of her protectors in 99949 Miepgies, along with 11572 Schindler and 69275 Wiesenthal. Virtually all authors, artists, and classical composers of any fame have asteroids named in their honor. Sometimes fictional creations rank more highly than their creators, as with the case of 5048 Moriarty, 5049 Sherlock, and 5050 Doctorwatson trumping their mutual creator, 7016 Conandoyle. Naturally, scores of scientists and explorers of the recent and distant past have since become namesakes for asteroids: 327 Columbia (for Columbus), 876 Scott (for Antarctic explorer Robert Falcon Scott), 1065 Amundsenia (for Roald Amundsen, who beat Scott by days to become the first person at the South Pole), and of course standards like 697 Galilea, 2001 Einstein, 2244 Tesla, 5102 Benfranklin, 5450 Sokrates, 5451 Plato, 7000 Curie, 7495 Feynman, 7672 Hawking, and 8000 Isaac Newton. Even religious figures have literal places in the heavens now, including 1840 Hus, 7100 Martin Luther, and the timely example of 8861 Ratzinger, named for Joseph Cardinal Ratzinger before he became Pope Benedict XVI (whose resignation is pending in just a few days as I write this).

Astronomers being human beings after all, it was probably inevitable that the first foray away from “serious” names was to use their discoveries to honor family members. Such tributes are no longer controversial in the twenty-first century—indeed, their dignity may compare favorably to the likes of 12373 Lancearmstrong or 17627 Humptydumpty—but had to be disguised as high-brow classical references in the nineteenth century. As early as 1856, 42 Isis seemed like a simple tribute to the ancient Egyptian mother-goddess, but its English discoverer Sir Norman Robert Pogson also had a daughter whose middle name was Isis. (Pogson is another giant in the field of observational astronomy, best known for fine-tuning and modernizing the ancient system of measuring star brightness by magnitude, and asteroid 1830 Pogson was later named in his honor.) Likewise, yet another Austrian-Czech astronomer and mathematician named Theodor von Oppolzer went on a familial naming spree in the late 1800s: 153 Hilda and 228 Agathe honor his daughters, and 237 Coelestina honors his wife, and of course he was posthumously honored with 1492 Oppolzer.

A kind of nineteenth-century ancestor of an Internet meme involved naming early asteroid names in subtle reference to a deeply respected French astronomer and pioneer sci-fi author named Camille Flammarion. Asteroid 107 Camilla was officially named for a queen from Roman mythology but was openly acknowledged as a gender-bent tribute to Flammarion. His first wife inspired 87 Sylvia (again, it officially honors a great name from Roman myth: Rhea Sylvia, mother of Romulus and Remus, the twin boys instrumental in the legendary founding of the city of Rome itself), while 154 Bertha and 654 Zelinda are alleged tributes to his sister and niece respectively. Flammarion’s novels inspired at least two early asteroids: 141 Lumen, from his novel about a race of intelligent plant-like aliens, and 286 Iclea, named for the heroine in another novel. After standards relaxed, 1021 Flammario was openly named for him with only the residual classical flourish of dropping the Gallic final N.

An early hint of the current state of affairs may be 453 Tea, which could be an acronym or some other coded reference to someone or something arcane but, if not, could just be a tribute to the beverage. Harmless fun with numbers can be found in the likes of 4321 Zero, 24680 Alleven, and 13579 Allodd. Someone honored the humble activity of typing with 6600 Qwerty. Contemporary Belgian astronomer Eric Walter Elst, with thousands of asteroid discoveries to his credit, must have been torn between dinosaurs and astronomy as a child, so he apparently split the difference in naming asteroids like 9937 Triceratops and 9949 Brontosaurus.

Popular music is a treasure trove of asteroid names: 3834 Zappafrank, 4305 Clapton, 7934 Sinatra, 19367 Pink Floyd, 19383 Rolling Stones, 19398 Creedence, 23990 Springsteen, 24997 Petergabriel, 44016 Jimmypage, and even 18132 Spector (yes, named for Phil; a future penal colony perhaps). Besides 8749 Beatles, numbers 4147 through 4150 honor the specific members of the band, while the consecutive placement of 17058 Rocknroll and 17059 Elvis seems only logical.

Wrapping up these anecdotes on asteroid names, an odd anomaly about Pluto’s 2006 demotion from full planethood is that its late addition to the roster of minor planets gives it the deceptively high permanent designation of 134340 Pluto.

Cinder and Soil
Whether sentimental or silly, proper names help differentiate asteroids for our convenience and even bare-bones numeric designations tell when each one was discovered, but neither names nor numbers reveal any practical or descriptive information about each particular asteroid. Given nothing else to work with, someone like me might be more inclined to send probes to 30439 Moe, 30440, Larry, and 30441 Curly than to, say, 6489 Golevka. As it turns out, those homages to the Three Stooges are garden-variety main-belt asteroids with low inclinations and low eccentricities, while Golevka has a razor-thin chance of colliding with Earth at some point in the distant future. The stooges may no longer even be particularly close to each other just because they happened to be when they were cataloged in the year 2000. It would be helpful to be able to categorize asteroids according to certain shared and noteworthy traits, but names alone convey no such information.

Here spectroscopy comes to the rescue by letting us analyze an asteroid’s chemical composition from across millions of miles of space. As recently as the 1970s, there was one nice and simple classification system for asteroids that sorted all of them into just three spectral categories. The details have since gone a little haywire but the core of this old system endures.

About three-quarters of all asteroids are C-types, so named because they’re carbonaceous (rich in carbon). C-types tend to have very low albedos—think of charcoal or graphite in pencils, both being mostly carbon and thus very dark—so they may be even more common than we already think simply because many go unseen against the background of deep space. The fourth-largest asteroid, 10 Hygiea, was only discovered after several smaller asteroids because Hygiea happens to be the largest C-type asteroid. Its albedo of only 0.07 makes it harder to find compared to, say, 3 Juno which is less than two-thirds of Hygiea’s size but has an albedo of 0.24 and so was discovered almost a half-century earlier.

About one asteroid out of every six is a stony or silicon-rich S-type. These have much higher albedos than C-types thanks to more reflective surface materials like magnesium silicate or iron silicate, two important components of ordinary dirt and rock here on Earth. For what it’s worth, these are probably closest to the public image of an asteroid as a giant free-floating boulder in space.

Some of the imbalance between the two categories is a mere matter of geometry. C-type asteroids are more common in the belt’s outer zone beyond that big 2.5 AU/3:1 resonance Kirkwood gap, leaving S-types more predominant in the inner zone. Remember that the inner zone of a disc—and yes, the asteroid belt is hardly a perfect disc, but its shape is close enough for this to apply—has less area than the outer zone even if the belt were split exactly at the midway point relative to its center. As things stand, the big Kirkwood gap is closer to the Sun than a true midpoint would be, which makes the inner/outer division even more imbalanced. It also turns out that 4 Vesta, 19 Fortuna, and 7 Iris are the only three of the twenty-five largest main-belt asteroids within the inner zone.

Besides the two main spectral types, less than one-tenth of all asteroids were originally lumped together as a sort of leftover category, X-types, but that name is hardly used anymore. Since the 1980s, two different and slightly contradictory systems of sorting asteroids into more specific groups have taken root, and covering the details of each system here could easily double the length of an already long essay. Both still include C-types and S-types but fine-tune each category into more specific sub-groups, often according to criteria like absorption patterns at certain ultraviolet frequencies that tend to scare away casual readers. A specific asteroid may be a garden-variety C-type according to one system but be pigeon-holed into some niche category in the other system, including a “category” covering only that one asteroid. Worst of all, the two systems sometimes use the same letter for different groups or, inversely, have similar groups marked by different letters. And besides these two main systems, there are others with even smaller followings.

You don’t need to be an astronomer to see that some serious housecleaning is overdue in the study and cataloging of asteroids (in fact, being a non-astronomer with no academic footing at stake might be an advantage). For all its weird consequences like demoting Pluto, the IAU’s 2006 definition of a planet stemmed from a healthy desire for standards and order that frankly would benefit the study of asteroids too. For the sake of salvaging as much brevity as possible (I really am trying), only two of the niche categories spun off from the old system are worth mentioning here.

Covering the smaller of the two first, both of the popular asteroid classification systems include V-types or vestoids. These are named for dominant member 4 Vesta and are similar in composition to S-types but with a tendency toward even brighter composite materials, especially a family of silicate minerals called pyroxenes that are often bound up with metals like iron, magnesium, and zinc. In fact, Vesta itself is the brightest of all asteroids with an albedo of 0.423 and can even be seen from Earth with the naked eye under great viewing conditions (don’t even bother if you live in a city). Dozens of smaller vestoids are known, but all of them combined would only amount to a tiny fraction of Vesta itself. The prevailing theory is that the are all chunks of Vesta broken off by an ancient collision, and a huge crater near Vesta’s south pole is a possible “smoking gun.” Besides pyroxenes, many vestoids and even a few similar meteorites that reached Earth are rich in a greenish mineral called olivine, the crude state of the vivid green gemstone peridot. Down here, olivine is especially common far beneath our surface in Earth’s mantle, implying that olivine-rich vestoids were once fragments of Vesta’s interior.

In terms of overall mass and especially by sheer headcount, vestoids are outnumbered by the third-most common spectral type of asteroids, M-types. The M stands for metal, and asteroids composed of nickel and iron are especially common in this category, but not all M-types have explicitly metallic compositions. A more constant feature is a higher albedo than the two main categories, and this can be accomplished by plenty of reflective but non-metallic substances. The biggest M-type asteroid by far is 16 Psyche, named for the female counterpart of Cupid/Eros. Psyche accounts for a respectable one percent of the entire mass of the asteroid belt and measures about 150 miles along its longest axis. Based on its spectrum, it may be a huge nugget of almost nothing but nickel and iron.

Psyche is also a minor footnote in the history of astronomy as a discipline. Like the planets, the first nineteen asteroids were all given unique and fairly complicated symbols to be used as shorthand by astronomers, but Psyche was the first beneficiary of a new system using a “symbol” of simply its number of discovery enclosed in a circle. This soon became our current system after the circle became mere parentheses for the sake of easier typesetting. The original symbols faced the inevitability of becoming horribly complex as more asteroids were discovered—this was back when the prospect of dozens still sounded like a lot—and were dropped for asteroids, though they are still used for planets.

Family Values
Besides spectral classes, there is a more tangible basis for sorting asteroids into groups. Whenever several asteroids share conspicuous similarities in spectral class and orbital characteristics, then a logical assumption is that these were all once part of a single larger body that has since been destroyed by an ancient collision. Such bodies belong to a common asteroid family. The concept was first suggested in 1918 by Japanese astronomer Kiyotsugu Hirayama, and so they are sometimes called Hirayama families. He originally identified three families, but more than thirty have been confirmed as of early 2013, with dozens more whose existence is still debatable. Headcounts for each family rise as constantly as any tally of asteroids, so any exact figures given here would be dated by the time I post this, but a reasonable and safely general assumption is that about a third of all known asteroids belong to families.

Each family is named for whichever member has the lowest permanent designation and hence was the first to be discovered. This usually but not always makes it the largest member of that family and sometimes even the parent body of all the other family members. Asteroids previously thought of as members or even namesakes of families are frequently reclassified as cases of cosmic mistaken identity called interlopers and are dropped from the family roster. This can be annoying when the family’s namesake is expelled, in which case the whole family must be renamed for the next-lowest-numbered member. Likewise, family names change when fresh data assigns a lower-numbered asteroid to an established family. This makes for especially confusing reading if a book or article is even just a few years old, especially given the fast pace of asteroid discovery. At least one prominent family has already been through two name changes.

Coding a table into a blog entry, the lazy way

One asteroid celebrity conspicuously missing from any major family is 3 Juno, the third asteroid to be discovered and still barely ranking among the top ten for sheer mass. A handful of tiny asteroids in similar orbits are believed to be physically related to Juno, but the largest is only six kilometers across and bears the humble moniker of (32326) 2000 QO62. Such small groups where every other member is obviously a tiny impact fragment of the parent body are called clumps instead of families.

Families and their implicit information about chemical composition will predictably draw more attention if and when asteroid mining becomes a practical venture, but the more immediate concerns are over where asteroids are, how they move, and what’s likely to be in their way. On that note, we turn from composition-based families to orbit-based groups.

More Like Orphanages Than Families
Just sunward from the orbit shared by Jupiter and its tag-along trojan asteroids, a kind of celestial desert with almost no asteroids extends from about five AU to about 4.2 AU. The minor planets found beyond this desert belong to categories exclusive to the far frontiers of the Solar System like centaurs, the outer planets’ trojans, and the whole menagerie of trans-Neptunian objects or TNOs, but these are all worthy of their own discussion some other time. For now, this already lengthy introduction will stick to those categories of minor planets confined to the inner Solar System.

With the main belt already covered is sufficient detail, that leaves a few categories that are either completely removed from the main belt or else cross it along only a portion of their orbits around the Sun. These groups are not families in the sense of sharing a common origin; instead they are unrelated objects of various spectral classes whose only commonality was the sheer chance of falling into such secure orbital positions. Each group probably contains a few families of truly related objects, but those are the exception rather than the norm here.

At about 4.2 AU from the Sun, the celestial desert ends with a remarkable asteroid group which serves as the outer sentries of the main belt. These are the Hildians, named for 153 Hilda, another asteroid found by that prolific Czech astronomer Johann Palisa in 1875. More than a thousand Hildians are known today and doubtless many more are still hidden simply because the group is more distant than the main belt. Large Hildians beside Hilda herself include 190 Ismene, 334 Chicago, 361 Bononia, and 499 Venusia, but most are small and unremarkable. Most Hildians are carbon-dominated C-types, but a few belong to more exotic spectral classes like D and P whose surfaces show the presence of volatiles, substances like methane and water ice that tend to boil away in the inner Solar System but remain frozen in the outer system. In that sense, Hildians are a little more like comets, Kuiper belt objects, and the tiny moons of the outer planets, but Hildians are still asteroids in the strictest sense because carbonaceous or silicaceous materials still account for most of their mass. Orbits of Hildians have semi-major axes falling between 4.2 AU from the Sun and roughly the outer fringe of the belt’s core region at 3.5 AU, leaving them locked in a 3:2 orbital resonance with Jupiter (meaning each Hildian orbits the Sun three times every time Jupiter orbits the Sun twice).

The Hildian Triangle. The white doughnut-shaped cloud is the main asteroid belt, the small green dots are Jupiter’s trojan asteroids (clustered on Jupiter’s orbit at Lagrangian points sixty degrees ahead and behind the planet itself), and the brown dots are Hildian asteroids. Their distinctive “dynamic triangular” distribution leaves Hildians clustered at three zones of relative gravitational stability: the two Lagrangian points, and a third point directly opposite of Jupiter itself (in the top right corner).
Source: Wikimedia Commons, based on data provided by the Minor Planet Center database in July of 2006. Uploaded 1 September 2006 by user Mdf, retrieved 24 February 2013.

Moving sunward past the Hildians and a much smaller second asteroid desert, we next find a group of asteroids straddling the outer edge of the main belt itself, the Cybelians. The group’s namesake is 65 Cybele, discovered in 1861 by German astronomer Ernst Tempel and named in honor of a goddess native to the ancient state of Phrygia but later revered throughout the classical world in the last few centuries before the triumph of Christianity. Each Cybelian has a semi-major axis of between 3.25 and 3.7 AU from the Sun, with most in a corridor between about 3.3 and 3.5 AU in a 3:2 orbital resonance with Jupiter. Other large Cybelians include 87 Sylvia, 107 Camilla, 121 Hermione, and 76 Freia (curiously, the first three all have at least one known moon). Most seem to be C-types, but the group has plenty of variety.

Hopping the main belt to its inner boundary lands us amidst the Hungarias. These asteroids have their semi-major axes just inside that first Kirkwood gap at 2.06 AU marking the point of 4:1 orbital resonance with Jupiter and the commonly accepted inner boundary of the main belt itself. Any object thrown inward of this gap finds itself stuck in the unusual position of being under stronger gravitational influence from welter-weight Mars than from giant Jupiter. Here, any asteroids orbiting close to the plane of the ecliptic are cleared away by Mars, leaving only those in orbits inclined by at least sixteen degrees to the ecliptic. But while the orbits of Hungarias are wildly inclined, they have very low eccentricity (nearly round orbits) and have both 9:2 orbital resonance with Jupiter and 3:2 orbital resonance with Mars.

Many Hungarias also belong to a family in the traditional sense. Namesake 434 Hungaria, found by Max Wolf in 1898 and named for Hungary, has an unusual spectral class E surface dominated by a bright mineral called enstatite. Many other Hungarias are also E-types, implying an actual familial connection with Hungaria itself at least for this sub-group. Despite the fact that all Hungarias are small—Hungaria itself is the biggest but only measures about twelve miles across—the brightness of E-types makes them relatively easy to spot. Other Hungarias belong to more mundane S and C spectral classes among others.

Rebels, Outlaws, Ne’er-do-wells Before leaving the main belt behind altogether, two small but exclusive groups break the rules by having their semi-major axes inside of the belt’s two main Kirkwood gaps at 2.5 AU and 3.27 AU, those gravitational highlands where asteroids are usually not allowed to loiter. They accomplish this feat by having orbits that are wildly eccentric, zipping in to mingle with the inner planets before tearing out into Jupiter’s neighborhood. None stay in these orbits for longer than a few thousand or even million years (fleeting by astronomical standards) before the gravity of Jupiter or one of the inner planets pulls them either into more stable orbits or, less ideally, into the planet itself. The headcount for both groups is still in the two-digit range and is unlikely to grow much higher.

Out in the 3.27 AU gap and locked in a 2:1 resonance with Jupiter are the more distant of these two groups, the Griquas. Their namesake is 1362 Griqua, a flyspeck less than twenty miles across that was discovered in 1935 by English-born astronomer Cyril V. Jackson and named for the Griquas, a culturally and racially mixed people native to Jackson’s adopted homeland of South Africa. The only other Griqua asteroid endowed with a name so far is 8373 Stephengould, discovered in 1992 by celebrated astro-spouses Eugene and Carolyn Shoemaker and named in honor of respected paleontologist and popular science author Stephen Jay Gould. All Griquas have highly eccentric orbits, with Griqua itself veering between a perihelion of 2.03 AU from the Sun and an aphelion of 4.41 AU.

Closer to the Sun, more numerous, and even more eccentric than the Griquas are the Alindas, a group of asteroids locked in a 1:3 orbital resonance with Jupiter as the price for having that all-important Kirkwood gap at 2.5 AU all to themselves. Their namesake, 887 Alinda, was one of Max Wolf’s discoveries and honors a city from ancient Asia Minor along the coast of modern southwestern Turkey. Other Alindas include 1429 Pemba, 1550 Tito, 1607 Mavis, 1915 Quetzálcoatl, 2608 Seneca, and 3360 Syrinx. While Griquas typically have eccentricities of about 0.3, Alindas are as high as 0.65 instead. Alinda itself will come within 7.6 million miles of Earth (about 32 times the distance of the Moon) in January of 2025.

Like Jupiter and the other outer planets, humble Mars has its own pack of trojans (sorry). As a quick recap of a post from back in 2010, imagine that the Sun and a particular planet are two of the three points on a cosmic triangle with sides of equal length. If you stick to the plane of the planet’s orbit, then the triangle’s third point can only be in one of two spots along the planet’s orbit: either sixty degrees ahead (the leading or L4 point) or sixty degrees behind (the trailing or L5 point). Joseph Louis Lagrange, a man who forgot more about math and mechanics than most of us combined will ever know, figured out back in 1772 that these two places act like gravitational “bowls” where any object lucky enough to wander into them will stay put more or less permanently unless knocked out by any intruding force. Jupiter has swarms of asteroids in its Lagrange points, and an early quirk of the naming convention left these all named for heroes from the Trojan War, hence the name trojans for all asteroids in a planet’s Lagrange points. By leading or trailing their mother planet in roughly the same orbit, trojans turn that orbit into a kind of celestial time-share condominium with one landlord and several seasonal tenants. Trojans and their mother planet never collide, but the mathematical ideal of a perfect triangle also never really happens. Instead, the imperfect world of reality leaves trojans wobbling in tadpole-shaped loops of differing eccentricities around the actual mathematical Lagrange point.

None of the inner planets have the enormous family of trojans that Jupiter has (to say nothing of Neptune, whose trojans may rival the number of objects in the main belt), but Mars does have at least four known trojans: 5261 Eureka, (101429) 1998 VF31, (121514) 1999 UJ7, and 2007 NS2. The only one in the L4 point sixty degrees ahead of Mars is 1999 UJ7, while the others are all in the L5 point sixty degrees behind Mars. Eureka itself was discovered in 1990 by astronomers David H. Levy (famous for co-finding Comet Shoemaker-Levy 9 which struck Jupiter in 1994) and Henry Holt and was named for the famous exclamation of discovery ευρηκα, meaning “I found it!”, first attributed to the ancient engineer Archimedes. Eureka belongs to an extremely rare spectral class, A-types, marked by a distinctive red hue. Martian trojans all keep at least half an AU between themselves and Earth.

Relatively Close Is... Well, Relative
At last, it’s time meet the asteroids in our own backyard: NEAs, the Near-Earth asteroids. Yet once again we find a seemingly practical and straightforward label that is hamstrung by the lack of a clear definition. In this case, the loose end is: What qualifies an asteroid as “near?” Surely this an issue worthy of public attention and clear language. Alas, that awaits another IAU conference.

For our purposes, a safely broad description of NEAs would be any asteroid whose orbit, at any point, takes it within the orbit of the planet Mars. If that sounds too sweeping and inclusive, that’s only because non-astronomers tend to picture the planets as being more-or-less evenly spaced like a column of ducklings following their mother (the Sun) just like they look in almost every diagram of the Solar System ever made. In fact, each planet’s distance from the next planet out is always progressively much greater than the gap between it and the previous planet heading sunward. This leaves the inner Solar System looking something like a lily pad in the center of a pond.

Imagine a disc as large as Jupiter’s orbit around the Sun (and so with a radius of 5.2 AU) containing a smaller disc covering everything within the asteroid asteroid to the Sun (with a radius of 2.6 AU). That still consigns part of the asteroid belt to the inner Solar System, but leaving the cutoff at exactly halfway to Jupiter makes for easier math even if it gives the inner zone an unfair advantage. Actually it’s not unfair enough, because that smaller disc has an area of only about 21¼ square AU, whereas the bigger circle covers almost 85 square AU. So the bigger circle has four times the area even though its radius is only twice as long. Handicap the inner system even more by restricting it to the orbit of Mars, and now it’s barely more than one-twelfth the size of Jupiter’s orbit. For a real sense of insignificance, a circle the size of Neptune’s orbit can hold nine hundred circles the size of Earth’s orbit. The fact that a third dimension needs to be considered only piles onto the outer system’s advantage; remember that most of the material is near the plane of the ecliptic, but “most” is not “all.” In the grand scheme of the entire Solar System, our celestial backyard is more like a celestial flower bed or even a window sill.

Having justified a seemingly generous definition of “near-Earth” (not so generous in the grand scheme of things), just what kinds of asteroids are too good to hang out with the main-belt crowds?

Amors, the First Asteroid Media Celebrities
Sticking with the trend of starting along the periphery and moving sunward, we can first dismiss a group whose chances of ever being literally “near Earth” are near zero. These are the Amors or “Mars-crossers,” a category already alluded to earlier with the discovery of 433 Eros in 1898. Broadly speaking, Amors are those asteroids which approach Earth’s orbit from beyond but never quite reach it or cross it. Quantifying that definition, their closest approach to the Sun can’t be less than Earth’s maximum distance from the Sun of about 1.02 AU. This is the first of these final groups whose data is well plotted on a categorical basis at the NASA/JPL Minor Planet Database, and the data for Feb. 26, 2013, lists a total of 3,648 known Amors.

We are now getting close enough to Earth that several asteroids from each category have name recognition among people who even casually monitor news about space. The group’s namesake is 1221 Amor, discovered in 1932 by Eugène Joseph Delporte and named for the Roman god of love who is better known today by the Greek name Cupid. At about twenty miles across, the largest Amor is 1036 Ganymed, a name easily confused with Jupiter’s largest moon Ganymede; both are named for one of Jupiter’s male lovers in myth. Found in 1924 by Walter Baade (hence its German-tinged spelling), Ganymed has a high orbital eccentricity of 0.537 that takes it out well past Mars to nearly 4.1 AU before swinging it back in to a perihelion of only 1.23 AU. Its next upcoming close pass of Earth will be on October 13, 2024, when it will be only 0.374 AU or about 34.8 million miles away.

Probably the most famous Amor is 433 Eros, the first to be discovered and the only one so far to be visited by a probe. (Unlike families, mere groups are under no obligation to be renamed if a lower-numbered asteroid is subsequently assigned to the group, hence the group still being called Amors instead of Erotians. That said, order of discovery still has its place, as will be seen in a moment.) This roughly cashew-shaped S-type asteroid was discovered simultaneously on August 13 of 1898 by Auguste Charlois at Nice, France and by Gustav Witt in Berlin. As was mentioned already, it was the first asteroid discovered to cross the orbit of Mars, making it the first NEA celebrity and a subject of intense study during two relatively close approaches in 1900-01 and 1930-31. The American space probe NEAR-Shoemaker entered into orbit around Eros in 2000 and landed on it on February 12, 2001, transmitting data for another two weeks. Eros passed within 0.17 AU of Earth (16.6 million miles or about seventy times the distance to the Moon) on January 31, 2012.

If you like sorting and categorizing, then Amors are the asteroids for you. The group is partitioned into four sub-groups based on specific location. Instead of the usual custom of naming each sub-group for a specific member, these simply take Roman numerals. They are covered here in reverse numeric order for the sake of sticking with the established pattern of moving sunward.

Starting at the greatest distance from the Sun, by far the smallest group are the Amor IV asteroids. These are defined as Amors with an average distance from the Sun that is beyond the outer limit of the main belt (3.57 AU from the Sun) but who still approach Earth in the course of their orbits. They have some of the most eccentric orbits of any asteroids known, some as high as 0.75, which makes all of them not only Mars-crossers but Jupiter-crossers too. The only objects more eccentric than Amor IV asteroids are comets and a freakish category of comet-like asteroids known as damocloids whose eccentricities get as high as 0.9, taking them from Earth’s neighborhood all the way out to the farthest edges of the Solar System, with semi-major axes among the outer planets.

Querying the JPL Small-Body Database on February 26, 2013, shows a grand total of sixteen Amor IVs, with 3552 Don Quixote the only one with a name and (85490) 1997 SE5 the only other one with a permanent designation so far. Don Quixote was discovered in 1983 by a team of astronomers at Berne, Swizterland’s Zimmerwald Observatory led by Paul Wild and named for that greatest of all heroes from Spanish literature. At about twelve miles across with a perihelion of only 1.216 AU, Don Quixote is what astronomers portently call a potentially hazardous object or PHO. Any asteroid that comes within 0.05 AU of Earth at some point and is large enough to cause local destruction if it hits Earth qualifies as a PHO. About one-tenth of all PHOs are Amors.

Accounting for about half of all Amors, the Amor III asteroids have semi-major axes within the main belt (greater than about 2.1 and less than about 3.6 AU from the Sun) but are still eccentric enough (0.4 to 0.6) to approach Earth. Most also approach Jupiter but only a handful like 5370 Taranis actually cross Jupiter’s orbit. Ganymed is the largest Amor III and indeed the largest Amor of all. Another giant Amor III mentioned in the section on asteroids named for financial sponsors is 719 Albert. Confusingly enough, the fact that Amor IIIs are within the main belt means they can overlap with categories like the Alindas and Hildians (887 Alinda itself is also an Amor III).

Amors with semi-major axes between the inner edge of the main belt at about 2.04 AU and the orbit of Mars at 1.52 AU from the Sun belong to the Amor II category. These are less eccentric than their outer siblings, with eccentricities of 0.17 and 0.52, and all are Mars-crossers. Querying the JPL Small-Body Database just now yields a total of 1291 Amor II asteroids or about a third of the entire group, including thirty-two with names and perhaps two hundred others with permanent designations. The superstar of the Amor II category is undoubtedly 1221 Amor itself. Others include 1627 Ivar, 3122 Florence, 3199 Nefertiti, 3908 Nyx (not to be confused with Pluto’s moon of the same name), 4055 Magellan, and 4487 Pocahontas.

Closest to Earth are Amor I asteroids with semi-major axes of no more than 1.523 AU from the Sun. JPL-SBD data for February 26, 2013, lists a total of 635 Amor I asteroids. None have eccentricities greater than 0.33, making them the least eccentric Amors of all, but their inclinations run the gamut from almost zero to as high as sixty-two degrees. Fewer than one hundred even have permanent designations, and the only five with names are 433 Eros, 1943 Anteros, 4947 Ninkasi, 15817 Lucianotesi, and 189011 Ogmios. A few like Eros are just barely eccentric enough to cross the orbit of Mars, but most form a kind of mini-belt between the orbits or Mars and Earth without every intruding on either.

There has been a suggestion for a new category whose parameters are still barely defined but potentially overlaps certain Amor I asteroids and a few of the NEAs discussed in the next section. Still more of a thought exercise than an actual proven category, these Arjunas are named for the heroic warrior Arjuna from Hinduism. Their existence was proposed by Dutch-born American astronomer Tom Gehrels, a kind of 21st-century throwback to old-school asteroid catchers like Wolf and Palisa whose youth was spent fighting Nazis in the Dutch Resistance. Together, Gehrels and spouses Cornelis Johannes van Houten and Ingrid van Houten-Groeneveld found thousands asteroids and comets before Gehrels’ death in 2011. Arjunas could be poetically described as “Earth shadows,” because they stick to neat and orderly orbits of slightly greater than one AU from the Sun with eccentricities of 0.1 or less, parameters that keep them close to Earth but without ever crossing our orbit. Entering those orbital parameters into the JPL-SBD database yields 122 matches, including not one with a name. The oldest of the bunch doesn’t even have a permanent designation yet: 1991 VG. A guesstimate of its size is only six to twelve meters across, which raises the embarrassing possibility that it may not even be an asteroid at all but rather a booster rocket or some other piece of loose space junk. Silly as that sounds, it becomes all the more likely as we get closer to Earth and observable objects get downright tiny.

Nearest of All
If Arjunas become an accepted category, the other existing group whose headcount will diminish is the first of the objectively near-Earth asteroids, the Apollos. An Apollo is any asteroid with a semi-major axis greater than Earth’s (exactly one AU from the Sun) but whose perihelion distance must be less than Earth’s aphelion distance of 1.017 AU. Group namesake 1862 Apollo was first discovered in 1932, but it was then lost until its rediscovery in 1973, which is why its number is lower than other Apollos discovered later. Named for the Greek god, the orbit of Apollo takes it through the orbits of Venus, Earth, and Mars. Measuring only about a mile across, it belongs to a rare metal-rich spectral type, Q. Other Apollos include 1866 Sisyphus (giant of the family at six miles across), 2101 Adonis, 1566 Icarus, 4015 Wilson-Harrington (the asteroid alter ego of Comet Wilson-Harrington; yes, the same body can be both a comet and an asteroid, but that’s a whole other story), 4179 Toutatis, and the already mentioned 6489 Golevka. Several of these are both Earth-crossers and PHOs with slim but measurable chances of hitting Earth at some point in the future.

The rap sheet of 4179 Toutatis is formidable: Apollo, Alinda, Mars-crosser, and potentially hazardous object (PHO). The odds of this asteroid named for an ancient Celtic god ever hitting Earth are beyond thin, but Toutatis currently ranks as the largest known PHO at about two and three-quarters miles long on its longest axis. Toutatis came within 0.05 AU of Earth in 2012 and will come within 0.0198486 AU (less than 1.9 million miles or about nine lunar distances) in 2069. China’s Chang’e 2 space probe took beautiful full-color photos of Toutatis during a close fly-by on December 13, 2012, but the copyright status of those photos is iffy. For the sake of caution and because it looks rather sinister, here’s a public-domain radar image of Toutatis taken in 1996 by JPL’s Goldstone Observatory in the Mojave Desert.
Image Credit: Steve Ostro, JPL/NASA

We now come to the realm of Earth trojans. Nothing has been discovered in the trailing L5 point so far, but one asteroid has been found in the leading L4 point. Still known simply as 2010 TK7, it is about 300 meters across with an eccentricity of about 0.19 but a hefty inclination of almost twenty-one degrees. This high inclination and the especially high “wobble” of its tadpole-shaped orbit sometimes brings 2010 TK7 as close as about one-seventh of an AU to Earth. If a trojan is ever discovered in Earth’s trailing L5 point, then assuming it has relatively low inclination, it would take dozens of times less fuel to reach such an asteroid than it does to reach the Moon even though the Moon is vastly closer just because the progression of the trojan’s own orbit basically accomplishes most of the work of getting there. Unfortunately, even if 2010 TK7 were trailing instead of leading, its high inclination makes it an even more fuel-consumptive destination than the Moon most of the time. It doesn’t look like many Earth trojans will ever be found, although surprises can’t be ruled out considering the problems of trying to observe a part of the sky only sixty degrees removed from the Sun (quite a different matter than staring out into deep space away from the Sun as with studying the main belt).

In Conclusion, the Scorchers
At long last, we come to those unfortunate asteroids whose semi-major axes are less than one AU from the Sun, the Atens. Namesake 2062 Aten was discovered in 1976 by another latter-day asteroid-catcher, Eleanor F. Helin who discovered a total of 872 asteroids and lead NASA’s Near Earth Asteroid Tracking team (NEAT) before her retirement in 2002 and death in 2009. The namesake of Aten is the Egyptian god of the Sun, a fitting name for something closer to the Sun than Earth is. The JPL-SBD lists a total of 758 Atens, including nine with names that are all taken from Ancient Egypt. Among them is recent media celebrity 99942 Apophis which whisked past Earth in February of 2013. Others include 2406 Hathor, 3362 Khufu, 3554 Amun, and 5381 Sekhmet.

Data collected so far shows that Atens tend to be wildly eccentric, and most still cross Earth’s orbit even though their semi-major axes are all closer to the Sun than Earth. One called (137924) 2000 BD19 has an almost comet-like orbital eccentricity of 0.895, taking in to less than nine million miles from the Sun (less than one-third of Mercury’s closest approach) before rolling out to 1.661 AU just past the orbit of Mars. But again, this may be an illusion caused by the fact that observing objects closer to the Sun is inherently more difficult than deep-sky observation. There may be many more Atens with more regular orbits that are simply too hard to see.

The tiny minority of Atens that never cross Earth’s orbit, so-called inner-Earth asteroids, are known by two conflicting names. The first recognized member of this class was 163693 Atira, found by the automated LINEAR asteroid-hunting program in 2003 and named for a Pawnee Indian goddess. Atira was the first confirmed inner-Earth asteroid, but the first suspected example was found in 1998 by astronomer David Tholen (creator of one of the two competing schemes for classifying asteroid spectral types). Tholen’s discovery was dubbed 1998 DK36, and his suggested name for the body was Apohele, the Hawaiian word for “orbit” which also coincidentally resembles “aphelion.” But 1998 DK36 was lost after its initial discovery and remains lost. It it is ever rediscovered, confirmed, and given the name Apohele, then the entire group will be known as Apoheles, but they’re Atiras for now. The JPL-SBD shows a total of twelve Atiras, including the truant 1998 DK36.

So far, there is no evidence of any trojans in the orbits of either Mercury or Venus, nor of any other asteroids in their vicinity for that matter. Back in the early twentieth century, some astronomers believed they had spotted a glimpse of a planet even closer to the Sun than Mercury that was tentatively named Vulcan after the Roman god of smiths. As a subtle tribute to this “planet that never was”, astronomers speculate about the existence of so-called Vulcanoids, a group of asteroids orbiting the Sun within the orbit of Mercury, but no evidence of their existence has been found yet either.

In closing, here are four quick asteroid celebrity lists:


Disclaimer/Citation/Bibliography/Boilerplate: I shamelessly used Wikipedia or my old Asimov books to fact-check the biographical and categorical information. The rest is courtesy of NASA/JPL. A lot of this would qualify as common knowledge in an ideal world. With any luck at all, it will someday. Thanks for reading.