Geotimes
Geophenomena New pursuit of near-Earth asteroids
Finding faults in Washington
New pursuit of near-Earth asteroids Tons of interplanetary material hit Earth every day. Most of that material is dust, but Earth and its moon show a record of collisions with much larger objects, with surprising regularity and incredible destructive force. As evidenced most famously by the Yucatan crater that marks a collision with an almost 10-kilometer-wide object, blamed for bringing about the demise of the dinosaurs, life on this planet could be very much at risk should another large space traveler hit it today.
This near-Earth asteroid measures about 58 kilometers long and 23 kilometers wide  -  large enough to be of some concern if it were ever to collide with Earth, an unlikely event. The now-defunct Galileo mission took images of the asteroid Ida on its way to Jupiter in 1993. Image courtesy NASA.
Though the likelihood of such an impact now is relatively small, this past summer, a team from NASA and an independent group of concerned astronomers separately released documents that called for more science on so-called near-Earth objects (NEOs). Although all the researchers admit that panic isn't necessary, they say some planning ahead is; the two documents, one a NASA report and the other an open letter to Congress and the public, particularly highlight concerns over smaller bodies that could hit the planet and have not yet been found. Using visible impact craters on other bodies in the solar system as a proxy, as well as other criteria, NASA researchers estimate that NEOs larger than 1 kilometer in Earth's vicinity number about 1,100. So far, a project nicknamed Spaceguard has found about 60 percent of those. The remaining 40 percent should be found within the decade (the goal is to find 90 percent by the year 2008). "The question has always been protecting ourselves against large impacts," says David Morrison of NASA's Ames Research Center in Mountain View, Calif. "The Spaceguard survey is designed to deal with those large asteroids and has done so very successfully." The two new reports raise the question of whether observers should look for the smaller ones, he says.
Smaller objects have the potential to do a lot of damage on their own, by landfall or creating tsunamis in the ocean. Anything bigger than 15 meters is large enough to get through Earth's atmosphere. But it's the objects that are about 50 to 100 meters across  -  estimated to number in the hundreds of thousands  -  to really worry about, says Don Yeomans, manager of the NASA Near-Earth Object program office in Pasadena, Calif. The higher numbers lead to higher likelihoods of an impact: The larger asteroids may hit only every half million years or so, but relatively smaller ones could ping Earth as often as once every millennium.
Asteroid observers know how easy it would be to nudge an object off its destructive course. "Decades of warning [give us] time to experiment with a variety of ways of changing the orbit," Morrison says. A slight bump with a remotely operated spacecraft or, as suggested by some, a well-placed nuclear explosion on an object's surface would change the trajectory of an object hurtling toward Earth by several centimeters a second. Either technique, Yeomans says, "would ablate the [outside], and the outgassing would introduce a rocket-like thrust." If a known object were calculated to hit in two decades, then just "a few millimeters per second in velocity change over 20 years would be more than enough," he says, to move an object off its course. If scientists catalog an Earth-collision-bound object even a decade before its predicted impact, they still have an adequate window of time to respond, Morrison says. Planning to move a smaller NEO would be easier than a 1-kilometer or larger object. Or, he says, "we could decide to just take it," and allow an impact to occur.
NASA submitted its report on Aug. 22. The team determined that it would take 20 years at most (starting in 2008) to catalog the smaller NEOs, in order to determine which have trajectories that might pose a threat. Such work would also take several hundred million dollars, a cost of risk reduction that the team balances against the costs of an impact.
Concerned astronomers, both amateur and professional (and unaf