TCS Daily


Asteroids and Oorts

By Charles Matthew Rousseaux - March 25, 2004 12:00 AM

Near misses don't come much nearer. At 5:08 pm EST last Thursday, an asteroid with the graceless name of FH 2004 whizzed by the earth, skimming a mere 26,500 miles over the Southern Atlantic Ocean. It was not large -- about 100 feet in diameter -- and so would have likely exploded in the atmosphere if it had hit the earth.

A larger object was detected, shortly before President Bush gave his speech on space policy in January, which by some calculations seemed headed straight for the earth. It eventually missed by a wide margin, but there would have been few options had its initial track been true.

Sometimes asteroids and comets don't miss, wreaking Hollywood-style havoc across the planet. Sixty-five million years ago, give or take a couple of Tuesdays, a largish chunk of rock made such a deep impact in the lives of dinosaurs that none of them survived. More recently, in 1908, a mid-sized object exploded over Tunguska, Siberia with a force of about 10 megatons, not-quite literally nuking about 2,000 square kilometers.

There are countless asteroids and comets in the solar system, debris from its formation four-and-a-half billion years ago. They range from micrometeorites which constantly pepper (and salt) the atmosphere to the distant planetoid Sedna. Only a fraction of those objects pose any sort of an eventual threat to earth, but just a fraction of that fraction have been surveyed, and it only takes one to make a significant change in the social schedules of most living things

Asteroid threats come in three sizes. Small asteroids, such as FH 2004 can explode in the atmosphere with nuclear force, potentially tripping twitchy fingers of new members to the nuclear club. Larger asteroids (or comets) of over 150 meters (450 feet) in diameter can penetrate the atmosphere, devastating cities or even states. Objects greater than about half a mile in diameter are potential civilization enders.

Recognition of that threat prompted NASA to start spending about $3.5 million annually on the Spaceguard Survey several years ago. The project is designed to find 90 percent of the largest near-earth objects by 2008. From an estimated population of over 1,200 such objects, it has found only one that could have a crushing encounter with the earth -- 1950 DA, which has a 1 in 300 chance of striking in 2880. A bill offered by California Rep. Dana Rohrabacher to expand the Spaceguard Survey to smaller objects is currently under Congressional consideration.

There are three large bands of material from which such threats can come. The first is the well-know asteroid belt located between Mars and Jupiter. Most known earth-threatening objects come from that region, pushed into potentially perilous paths by planetary gravitational fields. The second is the Kuiper Belt, a chillier big brother of the asteroid belt located just beyond the orbit of Neptune. It is thought to contain about 100,000 objects more than 300 miles in diameter, which if kicked inward become short-term comets. Hundreds of Kuiper Belt objects have been identified, including the planetoid Quaoar which was found in 2002. The recently discovered red colored mini-world Sedna -- 1,100 miles in diameter and 8 billion miles at it's closest to the sun -- sits between the Kuiper Belt and the Oort cloud. The Oort cloud is as far out and as frozen as one can go in the solar system. Located about half-way between the sun and its nearest stellar neighbors, it is believed to contain trillions of icy bodies, some of which are long-term comets. When the Oort cloud is perturbed by the passing of a nearby star -- as is thought to happen a few times every few hundred million years -- a shower of comets can fall into the inner solar system, with potentially catastrophic consequences for everything on earth. The great extinction at the end of the Eocene epoch about 36 million years ago could have been brought about by a series of comet impacts.

Even if an incoming asteroid or comet were detected in time for a deflection attempt to be made, there would still be a great deal of uncertainty about which way to do so. A nuclear warhead might simply break up a large solid object into many equally harmful chunks, and would do even less if the object were a floating rubble pile, as many are believed to be. Other strategies, such as using ion rockets or solar power would require years (if not decades) to be effective.

Studies to that end (and to avert that end) should continue to be pursued. Sooner or later, another large object will impact the earth with enough force to give everyone -- including Donald Trump -- a really bad hair day. The Spaceguard Survey and its possible successors serve as a small insurance policy against a majority of the earth's populace being fired (not to mention cooked). The search for small planetoids should continue, since even though the odds are astronomical, just like a casino, the house always wins.

Charles Rousseaux is an editorial writer for The Washington Times.


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