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90 Antiope
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Southwest Research Institute
Boulder CO |
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.
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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.
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 | 312920 |
| 6561 |
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| 1975 |
Total numbered asteroids |
2010 |
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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 6561 in
1975 to about
312900 in 2010. When you throw in
all the provisionally named objects, the grand total surpasses 574000.
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 NEAT’s principal
investigator. Spacewatch is operated by the University of Arizona’s Lunar and
Planetary Laboratory.
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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.”
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| 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
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 in true Zone fashion ultimately slips the trio a mickey and turns them
into mannequins.
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Joseph Legrange
who pioneered the math predicting Trojan orbits |
By mid 2011 there were over 2200 numbered and an additional 2400 un-numbered Jupiter
Trojans and 7 un-numbered Neptune Trojans. 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 most famous is 3753 Cruithne (KRIN-ya),
originally spotted by UK Schmidt Telescope staff observer Duncan Waldron 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 even at
its brightest it’s fainter than Pluto.
By 2011 three 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, rotates about its axis at a
variable speed. In late July of that year Martin Connors of Athabasca University in Alberta, Canada,
investigating with NASA's Wide-Field Infrared Survey Explorer, announced the confirmation
of a 300-meter-wide L4 object, 2010 TK7.
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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.
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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.
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| 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 near-miss anyone has observed was that of object 2011 CQ1 which
zipped by within 5471 km (3400 miles) of the ground on February 4, 2011. That’s
a quarter the altitude of orbiting GPS satellites. Fortunately 2011 CQ1 is only about
a meter wide, so even if it had struck it would have exploded high in the
atmosphere, harmlessly if powerfully at an equivalent of around a kiloton of TNT.
The previous record holder was an object designated 2004 FU162 with about
ten times 2011 CQ1’s mass. Latest figures cite over 800 potential impacts with
2004 FU162 between now and 2104 with a cumulative probability of 1 chance
in 16,000. As a cosmic casino, those are pretty good odds for our side. In case that
reassures you, though, consider that investigators are keeping tabs on another 130 or
so NEOs — that they know about — that might also
pass closely.
Text © Peter Blinn
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