Astronomers warn of possible hit by new-found asteroidAstronomers worldwide are tracking a mile-wide chunk of space rock to determine if a close encounter with Earth projected for Feb. 1, 2019 will be too close for comfort. Their efforts highlight what some scientists see as a need to focus scattered attempts to deal with threats from asteroids and comets, which have violently rewritten the history of life on Earth over billions of years.
On Wednesday, astronomers announced that asteroid 2002 NT7 has a small probability less than 1 chance in 200,000 of striking Earth during its 2019 flyby. Researchers expect this probability to shrink as they make more observations and use new data to refine calculations of the asteroid's position and orbit.
The asteroid was discovered July 9 by the LINEAR project, an automated search for near-earth asteroids conducted by the MIT Lincoln Laboratory in Lexington, Mass. The asteroid orbits the sun once every 2.4 years; astronomers say if it struck Earth, it would pack the explosive punch of 1.2 million megatons of TNT.
The asteroid's heft, uncertainties about its position, and the relatively short time for action if it proves dangerous have won it some of the highest initial hazard ratings ever for a newly discovered asteroid.
Still, "this object does not worry me in the least," says Gareth Williams, assistant director of the International Astronomical Union's Minor Planet Center in Cambridge, Mass. He notes that several times over the past few years, astronomers have discovered asteroids that first appeared to hold the potential for a collision with Earth but later proved to pose little or no threat.
The announcements of such discoveries might seem to be cases of astronomers crying, "Asteroid!," but Mr. Williams holds the process "is perfectly normal." As astronomers discover new asteroids, they calculate their orbits and their potential for impact with Earth. They then rate the object on two threat-rating systems developed over the past decade. Under both systems, astronomers see the chance that 2002 NT7 will collide with Earth as "extremely unlikely," but agree that it deserves close monitoring.
To date, scientists have discovered roughly 500 near-earth asteroids larger than a kilometer across, but they estimate that there may actually be up to 1,200 of them. Astronomers have placed a high priority on building a new 6.5 meter telescope that could spot hundreds more.
Thus, Williams notes, the public is likely to see additional warnings first raised then lowered as search efforts turn up new asteroids and comets. Though astronomers are concerned about being seen as "crying wolf," they say they would rather provide initial information and later ease a warning than face accusations that they withheld information if an asteroid turns out to have Earth in its crosshairs.
Yet if efforts to discover new near-earth asteroids are ramping up, efforts to prepare for a verified threat are "haphazard" and "unbalanced," says Clark Chapman, a researcher in the office of space studies at the Southwest Research Institute in Boulder, Colo. Few policymakers are prepared to respond to such a warning.
But that may be changing. Earlier this month, representatives from NASA, the Minor Planet Center, the US Space Command, and others met with House Space Subcommittee chairman Dana Rohrbacher (R) of California on Capitol Hill to discuss challenges and opportunities for asteroid-hazard mitigation.
Two approaches often discussed are: using some kind of rocket motor to deflect the asteroid, or as a last resort blowing it up before it reaches Earth. Dr. Chapman and colleagues Daniel Durda and Robert Gold have noted that before taking either of those steps, researchers must discover its composition and other characteristics. They propose placing small reconnaissance craft on orbit early, to shorten the time between alerts and scoiting missions. (Currently, it can take 18 to 24 months to launch such a mission.) Spacecraft designed to deflect or destroy asteroids also could be set on orbit to shorten response time. The trio estimates that with 30 years' warning, a space shuttle main engine could deflect a 1-kilometer-class asteroid.
For larger objects at shorter notice, explosives may be the only option, but this technique could lead to Earth's bombardment by asteroid fragments, which could prove more risky than a single, large impactor. "You can't go blindly in and nuke the thing as it comes by," Williams says.
Yet large impactors may not be the most serious immediate threat. In June, when the India-Pakistan crisis was at its height, US early-warning satellites caught a bright flash over the Mediterranean Sea a burst that released enough energy to match the atomic bomb that leveled Hiroshima, according to Brig. Gen. Simon Worden, deputy director of operations for the US Space Command. The cause: an asteroid, perhaps five to 10 meters wide.
Had the burst occurred at the same latitude a few hours earlier, "the results on human affairs might have been much worse," since Pakistan and India lack the sensors to distinguish between an asteroid and a nuclear explosion.
"This situation alone should be sufficient to get the world to take notice of the threat of asteroid impact," he says.