In 2005, Congress directed NASA to find 90 percent of near-Earth objects wider than 140 meters by 2020. But the agency now says it is limited in its current detection capabilities, and believes it will find just 50 percent of those objects by 2033.

Closing the gap

The report lists five strategic goals to guide asteroid threat response over the next ten years:

But beyond those goals, the report leaves most of the specifics up in the air.

"This isn't about any specific system, it's an overall structure across agencies to determine what the current capabilities are, and how we can enhance those capabilities, said Lindley Johnson, NASA's planetary defense officer, on a call with reporters. On the topic of finding 140-meter-plus asteroids, he said NASA likely needed "additional capability."

In particular, objects that cross Earth's path on their way out from the inner solar system are very hard to detect because they get lost in the Sun's glare. One proposed solution is NEOCam, an asteroid-hunting telescope specifically designed to sit between the Earth and Sun. But NEOCam's fate is up in the air, with the project only cleared to receive preliminary funding thus far. Johnson did not say whether the new report increases the chances NEOCam gets fully funded.

NASA's NEO catalog currently lists more than 18,000 objects, 8,000 of which cross the 140-meter size threshold. Once an object is discovered, it requires multiple followup observations by the worldwide astronomy community to determine whether it is hazardous.

"Some of those observations come from very capable amateurs," Johnson said. "Planetary defense is a team sport, and we welcome support from wherever it comes." The Planetary Society's Shoemaker NEO Grant Program provides such support. The program funds amateurs who contribute observational data to the NASA-funded Minor Planet Center. Aaron Miles, a senior policy advisor at the White House Office of Science and Technology Policy, said it is important that this amateur support continue.

"Amateurs and non-government individuals are already a very important fabric of this community," said Miles. "There's every indication that should be carried forward and strengthened."

Deflection

If we find an asteroid headed toward Earth, what can we do?

The report calls out three promising techniques: kinetic impactors, gravity tractors, and nuclear devices. A kinetic impactor simply slams into an asteroid, changing its course. Gravity tractors use the mass of a spacecraft to gravitationally tug on an asteroid, shifting its orbit without ever touching the asteroid’s surface. Nuclear devices are like kinetic impactors, with the increased energy from a nuclear detonation.

NASA's Asteroid Redirect Mission was considering testing the gravity tractor method, but that mission has been canceled. In 2021, NASA plans to try out the kinetic impactor technique with a spacecraft called DART (Double Asteroid Redirection Technique). DART would slam itself into a small, 150-meter-wide moon orbiting asteroid Didymos. The impact of the crash should change the moonlet's orbit enough to be observed by telescopes on Earth.