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Martian Curiosities
Martian Curiosities Brine ponds and possible biological activity

Asteroid Facts
Part I  [Part II]

90 Antiope
90 Antiope
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 cartoon dog bone, highly metallic but like Hyperion loosely packed with many voids. It tumbles end-over-end once every 5.4 hours.

Discoverer Robert Luther
Rubert Luther,
discoverer of both 90 Antiope and 288 Glauke
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 RC (“Pitbull”), 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 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.

 Total numbered asteroids 
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 6624 in 1975 to about 480800 in 2016. When you throw in all the provisionally named objects, the grand total surpasses 723000.

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.

Edison's Conquest of Mars
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 Kellaway
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.

Charles 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.

Joseph Legrange
Joseph Legrange
who pioneered the math predicting Trojan orbits
By late 2014 there were over 4050 numbered and an additional 2025 un-numbered Jupiter Trojans known and 9 un-numbered Neptune Trojans. Nothing yet appears to be pacing Saturn but as of mid-2014 at least three objects — 2002 GO9 (now officially known as asteroid 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). Seven more have been identified there since then and, remarkably, they and Eureka all consist of the green magnesium-iron mineral olivine. 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.

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 ‘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 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.

Hoba iron-nickel meteorite
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.

Solar System
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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