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.
216 Kleopatra has turned out to be a contact binary shaped like a dog bone,
highly metallic but like Hyperion loosely packed with many voids. It tumbles
end-over-end once every 5.4 hours.
JPL radar model of 1998 KY26
The slowest rotating asteroid known so far is 288 Glauke that grinds along at one revolution every 50 days.
According to a team led by Dr. Steven J. Ostro at JPL, the provisionally-named
1998 KY26 spins 6700 times faster or once every 10 minutes
42 seconds.
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, 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.
187546
4311
1970
Total numbered asteroids
2007
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. The graph shows how the
grand total of numbered asteroids has soared from 4311 in
1970 to about
187500 in 2007. When you throw in
all the provisionally-named objects, the grand total surpasses 414500.
LINEAR, which stands for Lincoln Near-Earth Asteroid Research, is operated by MIT and
funded by the US Air Force and NASA. NEAT is JPL’s Near-Earth Asteroid Tracking
program operating two 1.2 meter telescopes in Hawaii and California. When I worked at
JPL one of the other people whose office was in the same hallway, Ray Bambery, was (and still is) NEAT’s principal
investigator. Spacewatch is operated by the University of Arizona’s Lunar and
Planetary Laboratory.
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.
Serviss. 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.”
Cecil Kelloway
Though seriously wanting for scientific accuracy, two 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 a
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.
Chuck Beaumont wrote Episode 20, Elegy. Here, three astronauts crash-land on an
asteroid built up like a picturesque country village. All the people are frozen in place
but one, who startles them by introducing himself as caretaker Jeremy Wickwire (Cecil
Kelloway). 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 ultimately slips the trio a mickey and turns them into
mannequins.
Joseph Legrange who pioneered the math predicting Trojan orbits
By 2007 there were over 1100 numbered and an additional 1000 un-numbered Jupiter
Trojans and 5 un-numbered Neptune Trojans (with hints of hundreds more). Nothing yet
appears to be pacing Saturn or Uranus.
The first Mars Trojan to turn up was 5261 Eureka at the planet’s
L5 point (trailing 60 degrees behind). Since then the Minor Planet Center
has recognized two more at L5 and one leading Mars at L4.
Mars also has at least half a dozen companions that fall short of the Trojan category,
called co-orbitals.
The earth has company, too. So far the oddest is 3753 Cruithne (KRIN-ya),
originally spotted in 1986 but not fully appreciated until ‘97 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 it never wanders close enough for naked
eye visibility.
Hoba iron-nickel meteorite (Namibia)
Before our ancestors learned to smelt iron ore, they made do by chipping the metal from
iron-nickel meteorites. These come from asteroids which represent about 25% of the inner
solar system total. The remainder are stony or intermediate blends of the two, while many
Centaurs and others in the outer fringes, as previously discussed, lean more
toward ices. (We call these things comets if they outgas visibly, though lately
the line between asteroids and comets has blurred.)
The mineral resources up for grabs out there are staggering. Jeffrey Kargel
of the US Geological Survey in Flagstaff, Arizona estimates that 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
$300,000,000,000 and $5,000,000,000,000 by 1990 prices.
Less widely ballyhooed but potentially much more precious to spacefarers would be the
stony asteroids called carbonaceous chondrites. Ceres appears to be one of these. 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 cosmic pursuits, distance is far less important
than the change in velocity, delta-V, that 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 that are even more accessible.
So far the very smallest ∆Vs are for a couple of mysterious and possibly artificial objects,
2007 UN12 and 1991 VG at 3.856 and 3.998 kps. Named asteroids with the three smallest are 25143
Itokawa (a bizarre rubble pile the Japanese Hayabusa probe photographed in 2005),
4660 Nereus, and 65803 Didymos at 4.63, 4.98, and 5.1 kps. Eros also
looks pretty attractive at 6.069 kps.
We now know that sizeable asteroids have been swooping past the earth at alarmingly
small distances, all along, with no one being the wiser. And of course they don’t
always miss. As of 2006 the Earth Impact Database listed 174 confirmed impact features
from 15 meters to 300 km in diameter. The latter is South Africa’s Vredefort. The
dinosaur-killing Chicxulub in Mexico and the Sudbury in Canada measure 170 km and 250
km respectively. The youngest substantial impact features the EID shows are the Sikhote
Alin in Russia, dating from February 12, 1947, and the Wabar site in Saudi Arabia,
possibly as recent as 1891.
There’s quite a mob out there. The outermost circle is Jupiter’s orbit.
The best current estimates for the total asteroidal mass peppering the earth
annually hover around 35,000 tons. Most of this is dust, but US military
satellites typically register several aerial detonations yielding energies
between 10 and 1000 tons of TNT every year. An impactor of 75 meters might
deliver in the 2-megaton range and come along once every 1000 years or so.
Considering that’s roughly equivalent to 150 Hiroshima bombs, it would
obviously present a big problem. We can expect even larger collisions,
capable of threatening our survival as a species, to occur once every
several hundred thousand years.
So far the closest call anyone has observed was that of object 2004 FU162,
which zipped by at 15 kps within 6600 km (4100 miles) of the ground on March 31, 2004.
That’s a third the altitude of orbiting GPS satellites. Fortunately 2004 FU162 is
only about 6 meters wide, so even if it had struck it would have
exploded high in the atmosphere, harmlessly if powerfully at around 12 kilotons or 1 Hiroshima bomb.
Investigators didn’t announce the incident publicly until August 22. Having been
burned repeatedly by the popular press looking for sensationalistic headlines, they’ve
long ago become quite gunshy.
Anyway, latest figures cite over 800 potential impacts with 2004 FU162
between now and 2104 with a cumulative probability of 1 chance in 16,000. In case that
reassures you, consider that investigators are keeping tabs on another 130 or so NEOs
— that they know about — that might also pass closely.
