Asteroids?

The recent near impact of an asteroid with Mars, our northwest meteor flap, the highly visible lunar eclipse, and now the spy satellite shoot-down have certainly focused our attention on space in the last few weeks. As a predominately agricultural area, the majority of us are far more concerned with the timber, beef, and grain markets than we are with spaceflight, but still, space is a rather interesting area of scientific endeavor. It also generates a lot of curiosity in the public mind, and often a lot of national pride in most Americans. Like everything else however, the interest can’t last long in the minds of a fickle American public.

In recent years scientific research has been adopted by the “Chicken Little” set as their source of gloom and doom “the sky is falling” catastrophic threats to the world. These of course range from global warming to the threatened Bird Flu pandemic, from a giant asteroid impact to massive overpopulation. While the sky is not falling, and the world is not necessarily coming to an end anytime soon, all these threats do have some probability of happening. Generally a pretty low probability, but like everything else, I’d never say it can’t happen. The predicted Mars/asteroid impact didn’t occur, but Mars did have a pretty good chance of getting smacked by a flying rock. Sort of an interplanetary fender bender that had a lot of space scientists all excited. Based on the known orbital parameters available late in January, asteroid 2007 WD5 had a high probability of hitting the northern hemisphere of Mars, sometime in the evening of January 30th, 2008, with the best guesstimates at about a 4% chance of impact. WD5 is only about 160 feet across, which puts it a long way from being the “Planet Killer” so beloved of the science fiction movie writers. From a purely scientific viewpoint however, most of us with an interest in space happenings rather did hope it would hit. What a fireworks display!!

Assuming that the gentle reader has a working knowledge of meteors, comets, and asteroids, I’ll explain that 2007 WD5 is what’s known as an “NEO”, a Near Earth Object. An NEO is an inner system body (usually an extinct comet core or an asteroid) whose orbit periodically crosses that of Earth, and that often brings them fairly close to our little blue planet. WD5 was first discovered on November 20, 2007, after the object had already passed within 5 million miles of Earth on November 1. Astronomers calculated its course and noticed that it would be passing quite near Mars as well. NEO’s routinely pass close to Earth several times every year, and occasionally we get hit by them. Arizona’s half mile wide “Meteor Crater” is the aftermath of one such impact a few thousand years ago, and interestingly enough that rock just happened to be about the same size as WD5. The Arizona strike produced an explosion equivalent to about 2.5 megatons of TNT, or about 150 times the size of the A-bombs used on Hiroshima and Nagasaki. The inpact occurred during the Pleistocene epoch when the area was an open grassland dotted with woodlands and inhabited mostly by woolly mammoths, giant ground sloths, and camelids. I can just imagine the wildlife stampede when that thing hit!

A comparable incident occurred in 1908, when something exploded above the Tunguska region of Siberia, flattening trees in a 25-mile radius from the center of the blast. Scientists are pretty sure it was a comet or asteroid, considerably smaller than WD5 that was torn apart by its own shock wave as it plowed through the atmosphere. (UFO enthusiasts have long believed it was a flying saucer that somehow made it across light years of interstellar space, only to blow up above Russia.) The scientific explanation would account for the aerial explosion, and also the fact that no crater has been found. However, an Italian science team has recently measured seismic waves reflecting off a high-density spot in the bottom of a suspiciously crater-shaped Lake Cheko which lies quite close to the event's ground zero. It could be a piece of the original object and finding it could help investigators understand exactly what happened in 1908. If they find burned-out flying-saucer remains however…

Created by a much bigger object, the Chicxulub Crater underneath the Yucatan Peninsula is believed by many scientists to have brought about the end of the dinosaurs 65 million years ago. The crater is over 110 miles in diameter, making the feature one of the largest confirmed impact structures in the world. That particular asteroid or comet was at least 6 miles in diameter. Recent evidence suggests that the impactor was a piece of a much larger asteroid which broke up in a space collision more than 160 million years ago. Ahh… where’d the other pieces go?

While the potential Mars impact was interesting, it would be quite another story if 2007 WD5 were heading toward Earth. "Something of this size could take out a fairly large metropolitan area," said Donald Yeomans, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who manages the agency's (severely under funded) Near-Earth Objects program. It was this congressionally mandated search for potentially threatening asteroids and comets that turned up 2007 WD5 as a target in the first place. Originally identified as a possible risk to Earth, later analysis showed that the asteroid just might collide with Mars. While WD5 flew right on past Earth and Mars, that may not be good news for Earth, which will sometime again find itself in the asteroid's path. It would seem that even if they miss us this time, they keep coming back for another try.

Unlike the 1908 event, in the future we should have some warning of a possible strike, as well as (hopefully) the tools to divert the threat. We do have the technology to deflect something like this today, but before we send the Space Cadets out to blow it up with an A-bomb, we might remember that blowing one up Hollywood style will do little more than send a whole lot of slightly smaller fragments our way (somewhat like exchanging a rifle bullet for a shotgun blast). However, all we really need to do is slow it down a bit, which we could readily do with a nuclear rocket engine, if we start several years before it’s due to hit us. What we don’t have at present (thanks to congressional budget cuts and NASA’s constant dithering) is the means to reach an NEO with anything big enough to help.

For the moment however, we don’t even have any plans to save the Earth from a major NEO impact, nor any idea of what hardware we’d need. And unsurprisingly there are tens of thousands of them out there, ranging in size from little bitty things that we’ll never notice, to a lot of flying mountains several miles across. While the odds of an impact on any particular day are pretty slim, the question isn’t “if” one will hit us, it’s “when” will it hit us. We really do need to develop a means of defense, even if it's not a real high priority item. Meanwhile, congress keeps passing out earmarks while they can't find the money needed to keep NASA viable, and NASA seems to be asleep at the switch as well.