y Lee Billings * Posted April 16, 2008 11:38 PMUntil very recently, the devastating 1908 explosion of a space rockover the isolated Tunguska region of Siberia was thought to be aonce-in-a-millennium event. Based on comparisons to nuclear weaponblast effects, many experts estimated the Tunguska object to be 50 to 100 meters. But new simulations by Mark Boslough at Sandia NationalLaboratories suggest the Tunguska object was much smaller thanpreviously believed. And since smaller near-Earth objects (NEOs) are more common than larger ones, the implication is that the gap betweens uch impacts may be centuries rather than millennia."Chances are we're not going to discover one of these before it hits,"Boslough says, pointing out that the vast number of small NEOs faroutweighs the capabilities of the few surveys currently seeking them.
In 2005, the US Congress builtoff mandates from the 1990s, directing NASA to catalog 90 percent ofpotentially hazardous NEOs greater than 140 meters in diameter by the year 2020. Congress also asked NASA to study ways to deflectthreatening NEOs. But burdened with completing the International SpaceStation and replacing the Space Shuttle fleet, NASA has yet to allot funds to the project.
"Most Americans have faith that the federal government is doing what'snecessary to protect us against threats that could destroy our countryor leave large numbers of Americans dead," says US Representative DanaRohrabacher, who introduced legislation last December calling for NASAto devote more resources to NEO research. "The fact that we haven'teven formulated what our reaction would be to a potential threat fromspace is disturbing, considering the magnitude of the risk involved.You'd think there would be a plan ready, but there isn't."
Increasingly, coordinated private efforts are working to fill the gapin Earth's NEO defenses. Motivated in part by the upcoming USpresidential election, leading space scientists recently attended aninvite-only workshop at Stanford University to discuss shifting NASA'spriorities away from a return to the Moon and toward manned missionsto NEOs. And the B612 Foundation, a group co-founded by Apolloastronaut Rusty Schweickart, is gathering funds to test deflectionstrategies on an NEO by 2015. Earlier this year, Microsoft alumni BillGates and Charles Simonyi donated a combined $30 million to the LargeSynoptic Survey Telescope (LSST), keeping it on track for first lightin 2014. One of LSST's chief missions is to detect and catalog NEOs.As for Arecibo, Jim Cordes, a Cornell astronomer who frequently worksat the observatory, says that in the absence of government funding, aconsortium of universities may have to step in to fund the facility'soperations beyond 2010.Schweickart summarized what's at stake in a prepared statement at aNovember 2007 Capitol Hill hearing, where NASA and Congress clashedover how to address the NEO threat: "If we live up to ourresponsibility, if we wisely use our amazing technology, and if we aremature enough, as a nation and as a community of nations, there maynever again be a substantially damaging asteroid impact on the Earth.We have the ability to make ourselves safe from cosmic extinction. Ifwe cannot manage to meet this challenge, we will, in my opinion, havefailed to meet our evolutionary responsibility."