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Skip to: Asteroid novelties21,922 total numbered and namedEureka!Dreaming of asteroids

On the first evening of 1801, Palermo Observatory director Giuseppe Piazzi noticed an extra star through his telescope among the others in Taurus that didn’t seem to belong there. Its steady movement over the next few evenings convinced him he had found, at the very least, a new comet.

Aubrey Beardsley drawing
Piazzi notified other astronomers including Johann Bode, Jèrôme LaLande, and Baron Franz von Zach. Bode was the director of the Berlin Observatory and had published a mathematical “law” describing the relative sizes of the solar system’s orbits including that of a hypothetical planet between Mars and Jupiter. LaLande published planetary tables and had been Piazzi’s teacher, and von Zach edited a widely read astronomical journal and had taken to heart an ancient legend of a missing planet, also between Mars and Jupiter. Sir William Herschel’s discovery of Uranus twenty years earlier was still fresh on everyone’s mind.

Piazzi named his object Ceres Ferdinandea after Ceres, the Roman goddess of agriculture, and King Ferdinand III of Sicily. The greater astronomical community, recalling Herschel had originally named his discovery after Britain’s King George III, met him halfway and jettisoned the Ferdinandea.

Carl Friedrich Gauss (1777 1855)
Carl Friedrich Gauss (1777-1855)
Carl Friedrich Gauss derived Ceres’s orbit from Piazzi’s data and found it to vary between 2.5 and 3 astronomical units from the sun, confirming its placement between Mars (1.4 to 1.7 AU) and Jupiter (5 to 5.2 AU). By definition the average earth-sun distance is 1 AU. Modern nomenclature for asteroids whose orbits have been precisely plotted places a numeral for the order of discovery before the name, so you’ll see Piazzi’s discovery listed as 1 Ceres.

Asteroids Ceres and Vesta
1 Ceres and 4 Vesta shown to scale
Over the next six years other astronomers logged 2 Pallas, 3 Juno, and 4 Vesta. Ceres is the largest Main Belt asteroid with a diameter of around 940 km (580 miles) or about 27% the size of the moon. Though its surface gravity is only about 3% earth-normal, that’s enough to pull itself into a pretty good sphere as you can see here in the photo. Vesta is smaller but it’s the brightest asteroid as seen from the earth, at times marginally visible to the naked eye. After Vesta there was a 38-year slump, then Karl Ludwig Hencke discovered 5 Astraea and 6 Hebe in 1845 and ‘47.

Max Wolf (1863-1932)
James Watson (1838-1880)
<span class="generic-slide-caption" style="width:93px;"><i><aside>Max Wolf (1863-1932)</aside></i></span> <span class="generic-slide-caption" style="width:93px;"><i><aside>James Watson (1838-1880)</aside></i></span>

The total number of asteroids on the books reached an even 100 with James Craig Watson’s discovery of Hekate in 1868, but the floodgates really opened with astrophotography pioneer Max Wolf toward the end of the century. Up until this time astronomers had to depend on their eyes and hand-drawn charts, but a photographic plate exposed an hour or more as the telescope followed the star field with a clock drive would reveal asteroids as tiny streaks. Wolf himself eventually discovered 248 of them, from 323 Brucia (a Mars crosser) in 1891 to 1214 Richilde in 1932, the last year of his life. Among his most notable was 588 Achilles, the first of many Jupiter Trojans — asteroids that pace Jupiter within its orbit either 60 degrees ahead of it or 60 degrees behind.

Here are eight asteroids and likely former asteroids in descending order of size. For comparison, Hyperion at 270 km (170 miles) is roughly the width of Northern Ireland or Massachusetts; at the other extreme a person could walk the length of Gaspra, 12 km (7.5 miles), in about two hours. Hyperion, Phoebe, Amalthea, and Phobos are widely understood to be asteroids captured by Saturn, Jupiter, and Mars.

Hyperion moon of Saturn
Hyperion (270 km), a moon of Saturn
Phoebe moon of Saturn
Phoebe (214 km), also of Saturn
Amalthea moon of Jupiter
Amalthea (167 km), a close-in moon of Jupiter
Asteroid Mathilde
253 Mathilde (52 km)

Hyperion is icy and highly porous. Judging by the feeble pull it exerted on the Cassini probe it consists of about 40% empty space. Hyperion is also peculiar in that rather than rotating about a single axis it tumbles chaotically, so from its sky Saturn and the sun would swerve and rise and set in various directions. It reflects about 25% of the light that strikes it, similar in brightness to wet sand.

Phoebe1 is much darker, reflecting 6% or about the same as lampblack. It’s also about three times as dense as Hyperion.

Edward Barnard, after whom Barnard’s Star is named, discovered Amalthea in 1892. This was the first Jovian satellite to be discovered after Galileo Galilei’s original four in 1609. Odds are Amalthea’s colors come from sulphur from neighboring Io’s many volcanos.

Asteroid Ida
243 Ida (27 km) and its moon Dactyl
Phobos moon of Mars
Phobos (22 km), a moon of Mars
Asteroid Eros
433 Eros (18 km)
Asteroid Gaspra
951 Gaspra (12 km)

Ida was the first asteroid found to have a moon when the Galileo probe flew past it in 1993. It now appears such a thing is quite common. In the case of Ida, its moon Dactyl (the dot of light on the right) orbits once every 37 hours at an average distance of 108 km (67 miles).

Phobos is the larger of Mars’s two moons and very dark like Phoebe. For years investigators puzzled over the parallel grooves on Phobos until they realized they were formed by rubble which blasted into orbit during impacts and then spiraled back down over millennia and skittered to a halt in the sand. Phobos itself is losing about 2 cm of altitude per year and will either strike Mars or shatter into a ring in 30 to 80 million years.

Simulation Of NEAR Shoemaker Orbiting Eros ☆ NASA
Simulation of NEAR shoemaker orbiting Eros ☆ NASA
The NEAR‑Shoemaker probe orbited boomerang-shaped Eros every whichway and came to rest on it on February 12, 2001. Eros belongs to the category known as Near-Earth Objects (NEOs) whose orbits intersect with the earth’s. Eros isn’t considered a danger, though in the late sixties tabloid-fueled rumors warned of an impending collision with it that would do us in.

Some odd ones

So far, only 21,922 (4%) of the numbered asteroids are named. Currently the highest-numbered named asteroid is 560354 Chrisnolan.

Astronomer Beatrice Tinsley
Astronomer Beatrice Tinsley
The asteroid with the longest name is 4015 Wilson-Harrington at 17 characters.2 Some of the runners-up at 16 characters are 1914 Hartbeespoortdam, 2039 Payne-Gaposchkin, and 3087 Beatrice Tinsley… [skipping to the higher-numbered]… 172315 Changqiaoxiaoxue, 274843 Mykhailopetrenko, and 283990 Randallrosenfeld.

The shortest names are 85 Io (not to be confused with the Jovian moon Io), 954 Li, 1714 Sy, 2705 Wu, 3271 Ul, 6498 Ko, 16563 Ob, 22260 Ur, and 366852 Ti. First and last in the phonebook would currently be 20813 Aakashshah, named after a science fair-winning New Jersey medical student; and 22521 ZZ Top. Someone even honored their keypad with 6600 Qwerty.


There’s 13681 Monty Python, as well as 9617 Grahamchapman, 9618 Johncleese, 9619 Terrygilliam, 9620 Ericidle, 9621  Michaelpalin, and 9622 Terryjones. You’ll also find 3834 Zappafrank and 4147 Lennon, 4148 McCartney, 4149 Harrison, and 4150 Starr. 15845 Bambi and 16626 Thumper are named after the Disney characters and 3252 Johnny, 4238 Audrey, and 7707 Yes are named after Johnny Carson, Audrey Hepburn, and the British progressive rock band Yes. There’s no No, but a 2857 NOT, named after the Nordic Optical Telescope.

Baron Albert Salomon von Rothschild
The International Astronomical Union would likely throw a fit nowadays if someone tried to pay for the privilege of naming an asteroid, but things were much more casual back in 1885. When discoverer Johann Palisa auctioned it off for 250 Bettina, the winning bidder at £50 was Baron Albert Salomon “Salbert” von Rothschild. He named it after his wife, Bettina Caroline, who was also born a Rothschild. Palisa made minor history again years later when he named another one of his discoveries, 932 Hooveria, after then-future president Herbert Hoover in honor of his work directing relief operations in Europe in the wake of World War I.

216 Kleopatra Simulation From Radar Data
216 Kleopatra simulation from radar data
Asteroid 90 Antiope consists of twin spheres separated by a 60 km (37 mile) gap and orbiting about a common center of mass once every 16.5 hours. The sight of one from the other’s surface would be quite unnerving, taking up much of the sky. Carrying this concept a bit further, 216 Kleopatra has turned out to be a contact binary shaped like a ham bone. It tumbles end-over-end once every 5.4 hours and has two tiny moons, Alexhelios and Cleoselene, named after two of Cleopatra’s children with Marc Antony.

One of the slowest-rotating asteroids is 288 Glauke which grinds along at one revolution every 50 days. At the other extreme you have asteroid 2014 “Pitbull” RC, spinning over a quarter of a million times faster or once every 15.8 seconds. This was the same body that skimmed over New Zealand on 7 September 2014 with only 39,900 km (24,800 miles) to spare.

5145 Pholus Co Discoverer David Rabinowitz
5145 Pholus co-discoverer David Rabinowitz
Asteroid 5145 Pholus stands out by its vivid red color. About 185 km (115 miles) wide, it belongs to the Centaurs, icy bodies orbiting between Jupiter and Neptune and from which Saturn may have snatched Phoebe. Best guesses for Big Red’s composition so far call for a mixture of frozen wood alcohol, soot, olivine (from which the gemstone peridot is the ultrapure extract), hexamine (used earthside as an antibiotic and camping fuel), and organic compounds called tholins already known to be responsible for the deep orange color of Saturn’s moon Titan.

More discoveries

The LINEAR project, NEAT, and Spacewatch currently represent the state of the art in the automated search and documentation of asteroids and especially Near-Earth Objects which might pose a threat of impact. These three parties have discovered over 200,000, 28,000, and 11,000 asteroids respectively.

From the latest reports there are 10,447 Jupiter Trojans known and 27 Neptune Trojans. Nothing yet appears to be pacing Saturn but as of this writing at least three objects — 83982 Crantor, 2010 EU65, and 2011 QF99 — have been confirmed for Uranus.


The first Mars Trojan to turn up was 5261 Eureka at the planet’s L5 point (trailing 60 degrees behind). Eight more have been identified there since then and, remarkably, they and Eureka all consist of that same green mineral olivine mentioned above. At least one asteroid, 1999 UJ7, leads Mars at L4. Mars also has at least half a dozen companions that fall short of the Trojan category, called co-orbitals.

Heliocentric view of Cruithne’s orbit  ☆  Jecowa [CC]
Cruithne’s kidney bean-shaped path from Earth’s perspective  ☆  Jecowa [CC]
<span class="generic-slide-caption" style="width:240px;"><i><aside>Heliocentric view of Cruithne’s orbit  ☆  Jecowa [CC]</aside></i></span> <span class="generic-slide-caption" style="width:240px;"><i><aside>Cruithne’s kidney bean-shaped path from Earth’s perspective  ☆  Jecowa [CC]</aside></i></span>

The earth has company, too. One of the more interesting so far is 3753 Cruithne (KRIN-ya), originally spotted by UK Schmidt Telescope staff observer Duncan Waldron in 1986 but not fully appreciated until 1997 when Paul Wiegert and Kimmo Innanen at York University in Toronto and Seppo Mikkola at the University of Turku in Finland plotted out its byzantine path. From our perspective it gyrates through what’s called a horseshoe orbit, at times lagging the earth on its way around the sun and at other times racing ahead of it. Some call Cruithne a “second moon” but even at its brightest it’s fainter than Pluto.

By 2014 six more earth co-orbitals had been added to the list as well as a leading (L4) Trojan. At least one of those co-orbitals, 54509 YORP, spins about its axis at an accelerating speed. At the moment YORP makes one rotation about every 5 hours, but into the far distant future that’s expected to increase to around once every 20 seconds — at which point it will fly apart.

Artist’s Impression Of
Artist’s impression of 'Oumuamua ☆ ESO/M. Kornmesser
The first interstellar asteroid was discovered on 19 October 2017 by Robert Weryk, NEO Postdoctoral Fellow at the University of Hawaii at Manoa. I1 ʻOumuamua3 is reddish, cigar-shaped at around 30 meters100 feet wide and 180 meters600 feet long, and rotates once every eight hours. It dove in at a 123 degree angle to the plane of the solar system from the direction of the constellation Lyra, whipped around the sun, then made its closest approach to the earth on its way out at a distance of over sixty times that of the moon on 17 October of that year.4

Floating treasure

Meteoritic iron axe, found in Alaska
Tutankhamun’s iron dagger, ca. 1325 BCE
<span class="generic-slide-caption" style="width:130px;"><i><aside>Meteoritic iron axe, found in Alaska</aside></i></span> <span class="generic-slide-caption" style="width:130px;"><i><aside>Tutankhamun’s iron dagger, ca. 1325 BCE</aside></i></span>

Before our ancestors learned to smelt iron ore, they scavenged the metal from iron-nickel meteorites. These come from asteroids representing about 25% of the inner solar system total. The remainder are stony or intermediate blends of the two, while the Centaurs and others beyond lean more toward ices.5

The mineral resources up for grabs out there are staggering. Jeffrey Kargel of the US Geological Survey in Flagstaff, Arizona estimates even a trifling 1-kilometer-wide metallic asteroid would yield 400,000 metric tons of metal (not just the iron and nickel, but many others including gold and platinum) worth between $500,000,000,000 and $9,000,000,000,000 by 2016 prices.

Martian Moon Phobos, Largely Carbonaceous Chondrite
Martian moon Phobos, largely carbonaceous chondrite
Less widely ballyhooed but potentially much more precious to spacefarers would be the stony asteroids called carbonaceous chondrites. They’re rich not only in water but kerogen, that petrochemical ooze that Russia, China, and Brazil currently extract from oil shale. Give or take a zero or two, science writer and space colony advocate Marshall Savage estimates there are at least 1,000,000,000,000,000 tons of kerogen out there.

When it comes to asteroid mining or other gainful cosmic pursuits, distance can be far less important than the change in velocity, delta-V, you need to intercept your target. The minimum ∆V to reach the moon from low earth orbit is 6 km (3.4 miles) per second, but we know of over 600 NEOs even more accessible. So far the very smallest ∆Vs are for a couple of mysterious and possibly artificial6 objects, 2007 UN12 and 1991 VG at 3.8562.396 miles and 3.9982.484 miles kps. Named NEOs with the three smallest are 25143 Itokawa (a bizarre rubble pile the Japanese Hayabusa probe photographed in 2005), 4660 Nereus, and 65803 Didymos at 4.632.877 miles, 4.983.094 miles, and 5.13.2 miles kps. Eros also looks pretty attractive at 6.0693.77 miles kps.

Once upon a time

Asteroids have long been a staple of speculative fiction. One of the earliest such references was in the 1898 serial Edison’s Conquest of Mars by Garrett P. Serviss7. In the process of hunting down Martians (so much for multiculturalism) a fleet of earthly spaceships encounters an asteroid:


For a moment we were startled beyond expression. The truth had flashed upon us. This must be a golden planet — this little asteroid. If it were not composed internally of gold it could never have made me weigh three times more than I ought to weigh.

“But where is the gold?” cried one.

“Covered up, of course,” said Lord Kelvin. “Buried in star dust. This asteroid could not have continued to travel for millions of years through regions of space strewn with meteoric particles without becoming covered with the inevitable dust and grime of such a journey. We must dig down, and then doubtless we shall find the metal.”

Though seriously wanting for scientific accuracy, a couple of my favorite asteroid tales come from the first season (1959-60) of the anthology TV series The Twilight Zone. The first was Episode 7, The Lonely, written by Rod Serling. Jack Warden stars as Jim Corry, a prisoner sentenced to 40 years of solitary confinement on a thoroughly desolate and dispiriting “Ceres-XIV.” An android in the form of Jean Marsh keeps him company.

<span class="generic-slide-caption" style="width:110px;"><i><aside>Warden</aside></i></span> <span class="generic-slide-caption" style="width:110px;"><i><aside>Kellaway</aside></i></span>

Charles Beaumont wrote Episode 20, Elegy. Here, three astronauts crash-land on an asteroid built up like a picturesque country village. All its inhabitants are frozen in place but one, who startles them by introducing himself as caretaker Jeremy Wickwire (Cecil Kellaway). They learn the asteroid is a mausoleum in which the deceased are posed permanently in tableaux celebrating their fondest earthly aspirations. Wickwire plays the gracious host, but in true Zone fashion ultimately slips the trio a mickey and turns them into bio-mannequins. He summarizes, “While there are men, there can be no peace.”


1. Like the songbird it’s FEE-bee; in the the original Greek, PHOY-bee.

2. Though the International Astronomical Union imposes a strict 16-character limit, 4015 Wilson-Harrington was grandfathered as it was previously known as Comet Wilson-Harrington, discovered in 1949 and named after its co-discoverers.

3. The IAU has chosen to designate interstellar asteroids with a capital letter I followed by a numeral indicating the order of discovery, I1 ʻOumuamua being the first. ʻOumuamua (pronounced Oh moo-uh moo-uh) is a Hawaiian term characterizing the object as a messenger or scout.

4. NASA tells us it would love to send a probe to catch up with 'Oumuamua, but its whopping delta-V of 60 km/s is beyond current tech using chemical propulsion.

5. We call these objects comets if they outgas visibly, though the line between asteroids and comets has always been blurry.

6. Spent 70s-era rocket fuel tanks have been suggested, though from the objects' behavior they appear too dense for that.

7. Though now mostly forgotten, Serviss (1851-1929) was an enormously popular astronomy lecturer and authored many books on the subject.

Special thanks:

Ceres and Vesta ☆ NASA/JPL;
Hyperion, Phoebe ☆ Cassini-Huygens/NASA;
Amalthea, Ida, Gaspra ☆ Galileo/NASA;
Mathilde, Eros ☆ NEAR - Shoemaker;
Phobos ☆ HiRISE/NASA;
NEAR Shoemaker and Kleopatra simulations, Rabinowitz photo ☆ NASA;
Cruithne orbit animations ☆ Jecowa (CC);
'Oumuamua simulation by the European Southern Observatory (ESO) / M. Kornmesser

~ This page has made use of data and/or services provided by the International Astronomical Union’s Minor Planet Center. ~


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