NASA administrator and White House science adviser brief Congress on the asteroid threat

To date, NASA has identified 95% of the roughly 1000 near-Earth objects large enough to destroy civilization if they collided with the planet. However, the agency has only been able to find about 10% of the estimated 13 000 to 20 000 NEOs that are massive enough—140 meters in diameter or larger—to destroy a city. At current budget levels, the space agency will miss by 10 years the 2020 congressional deadline to locate 90% of those “city killers,” NASA administrator Charles Bolden told the House Science, Space, and Technology Committee.

According to presidential science adviser John Holdren, who testified on 19 March, the impact of a 140-meter asteroid would release as much energy as 50–500 megatons of TNT, but the probability of that occurring in any given year has been estimated to be only 1 in 30 000. A strike from a 1-kilometer-diameter asteroid would release more energy than was contained in the entire combined arsenals of the US and former Soviet Union at the height of the cold war—sufficient to potentially extinguish humankind. Of the NEOs of that size that have been located, none is on a course to threaten Earth, he said.

Bolden and Holdren told the committee that it could take four to five years to mount a campaign to deflect an asteroid headed toward Earth. The Department of Defense and NASA have run deflection exercises, but Holdren said that more work needs to be done, such as continued research into NEO characteristics, enhanced computer simulations, both manned and unmanned asteroid investigations, and further R&D on deflection, including explosives technologies and impact scenarios. One plausible method of interception could be to blast the object with a laser, which would blow off jets of material and propel the object off its course, Holdren said. President Obama’s plan to send a manned mission to a NEO by 2025 “will generate invaluable information for use in future detection and mitigation efforts,” he added.

The US should step up efforts to locate smaller NEOs, Holdren said. “With our current or near-future capabilities, both on the ground and in space, it is unlikely that objects smaller than 100 meters in diameter on collision courses with the Earth will be detected with greater than weeks of advance warning—a matter of some concern since the larger objects in this range could be city-destroyers.”

The detection of NEOs is a “major science driver” for the Large Synoptic Survey Telescope, which is due to begin operation in 2020, Holdren said. NSF and the US Air Force are cooperating with NASA, as is the Canadian Space Agency, which launched its Near Earth Object Surveillance Satellite in February.

The Sentinel spacecraft, a space-based infrared survey observatory proposed by the nonprofit B612 Foundation, aims to discover and catalog 90% of NEOs that are 140 meters and larger. The spacecraft, which is scheduled for launch in 2017–18, should also discover a significant number of smaller asteroids down to a diameter of 30 meters. Sentinel, which will be launched into a Venus-like orbit around the Sun, will scan the entire night half of the sky every 26 days with its 51-centimeter-diameter mirror during a 6.5-year-long mission. The foundation expects to raise $450 million over 12 years to fund the project.

The 17-meter asteroid that struck Chelyabinsk, Russia, on 15 February was estimated to have released as much energy as 400 kilotons of TNT. Asked how the 11 000-ton object had gone undetected, Holdren explained that it had come from the direction of the Sun, whose brightness made it unobservable. On the same day, the 45-meter asteroid 2012 DA14 passed nearly 27 700 kilometers from Earth, a close flyby that had been predicted many months in advance. Using tracking data and orbit calculations, federal agencies concluded over a year ago that the DA14 asteroid did not pose a threat to Earth, the International Space Station, or satellites in orbit, Holdren said.