On the first evening of 1801, Palermo Observatory director
Giuseppe Piazzi noticed an extra dot in his telescope among
the stars in Taurus that didn’t seem to belong there. Its steady movement over the
next few evenings convinced him that he had found, at the very least, a
new comet.
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.
Carl Friedrich Gauss
Piazzi named his object Ceres Ferdinandea after Ceres, the Roman goddess of
agriculture, and King Ferdinand III of Sicily. The greater astronomical community,
recalling that Herschel had originally named his discovery after
Britain’s King George III, met him halfway and jettisoned
the Ferdinandea.
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.
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 or about 27% the size of the moon. Though its surface gravity is only about
2.75% earth-normal, that’s enough to pull itself into a pretty good sphere as you can see
here in the Hubble 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.
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, 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 some of the best closeups available of asteroids and likely former asteroids with
their sizes shown as a percentage of the moon’s. Hyperion, Phoebe, Amalthea, and Phobos are
widely understood to be asteroids captured by Saturn, Jupiter, and Mars. All eight of these bodies are
much smaller than Ceres and their surface gravities vary between 0.02% and 0.4% of earth-normal.
Hyperion (Saturn)
Phoebe (Saturn)
Amalthea (Jupiter)
253 Mathilde
270 km dia or 8%
214 km dia or 6.1%
167 km dia or 5%
52 km dia or 1.5%
Cassini-Huygens/NASA
Cassini-Huygens/NASA
Galileo/NASA
NEAR - Shoemaker
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.
Phoebe is much darker, reflecting 6% or about the same as lampblack. It’s also
about three times as dense as Hyperion. (Like the songbird it’s FEE-bee,
though the original Greek was PHOY-bee.)
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.
243 Ida + Dactyl
Phobos (Mars)
433 Eros
951 Gaspra
27 km dia or 0.8%
22 km dia or 0.6%
18 km dia or 0.5%
12 km dia or 0.35%
Galileo/NASA
HiRISE/NASA
NEAR - Shoemaker
Galileo/NASA
Ida was the first asteroid found to have a moon when the Galileo probe flew past it in
1993. It now appears that 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 that
they’re caused 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.
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.
So far only 14807 (8%) of the 187546 numbered asteroids are named.
Currently the highest-numbered named asteroid is 188847 Rhipeus.
The asteroid with the longest name is 4015 Wilson-Harrington at 17 characters. Some of
the runners-up at 16 characters are
1506 Toulouse-Lautrec,
1914 Hartbeespoortdam,
3087 Beatrice Tinsley,
3903 Kliment Ohridski,
4534 Rimskij-Korsakov,
6304 Josephus Flavius,
21873 Jindřichůvhradec,
22907 van Voorthuijsen,
23889 Hermann Grassmann, and
24837 Mšecké Žehrovice.
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, and 22260 Ur. First and
last in the phonebook are currently 3654 AAS (American Astronomical Society) and
2098 Zyskin, named after a professor at the Crimean Medical Institute. 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 (“Zappa” was taken and there
were already 13 beginning with “Frank”) and
4147 Lennon,
4148 McCartney,
4149 Harrison, and
4150 Starr. 15845 Bambi and 16626 Thumper are named after the
Disney characters; 4945 Roachapproach after New Age musician Steve Roach; 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.
Hoover
People don’t ordinarily pay for the privilege of naming an asteroid, but 250
Bettina stands as an exception. When discoverer Johann Palisa auctioned it off, the
winning bidder at £50 (over $5000 in modern money) 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 future president
Herbert Hoover in honor of the latter’s work directing relief operations in
Europe in the wake of World War I.
