Jason DavisJun 20, 2018

New report explores threat from near-Earth asteroids

A new report released today outlines the threat from nearby asteroids and whether or not we're prepared if we find one headed toward Earth.

The report, issued by the White House's Office of Science and Technology, with support from with NASA and other government agencies, is formally called the "National Near-Earth Object Preparedness Strategy and Action Plan." It says we're probably not in danger of going extinct from a dinosaur-killer-sized asteroid, but exposed to a lot more risk when it comes to smaller objects. The authors also said we need to improve our ability to quickly launch reconnaissance and deflection missions when potential threats are found.

Sweat the small stuff

The report's best news is that when it comes to giant asteroids like the 10-kilometer-wide object that killed the dinosaurs, we don't have to be too concerned.

"NASA is confident that it has discovered and cataloged all near-Earth asteroids large enough to cause significant global damage and determined that they are not on collision courses with Earth," the report says, while noting that this does not necessarily include faint comets on the outer reaches of the solar system. (The report does not address the odds of such a comet impacting Earth.) NASA officials also said today they believe they have found 95 percent of near-Earth asteroids more than a kilometer wide.

But it's harder to find mid-size asteroids, some of which are still big enough to cause continent-wide damage. And when you consider even smaller objects that could wreak regional and city-scale devastation, the threat increases substantially. In 1908, an asteroid just 50 meters wide exploded over Tunguska, Russia and leveled more than 2,000 square kilometers of forest. If a similar event happened over a populated region like New York City, it could cause "millions of casualties," the report says.

Area of destruction of a Tunguska-sized asteroid
Area of destruction of a Tunguska-sized asteroid Image: OSTP

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."


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.

DART concept poster
DART concept poster Image: NASA / JHUAPL

It might not be immediately clear which of the three deflection techniques would work best, even after an asteroid bound for Earth is detected.

"We may need to send a reconnaissance mission," said Miles. "One of the actions called for in this report is to develop a concept for a more rapid reconnaissance mission." NASA currently requires a long lead time to build and launch a mission, and that doesn't count the travel time to the asteroid.

"It does take on the order of years to be able to implement a deflection mission in space," Johnson said. "The minimum of time I would ever want would be 10 years."

Warning the public

Suppose a threatening asteroid is found, and models show there's a chance it could hit a populated area. What then?

In NASA's case, the response plan involves notifying the White House and federal agencies to coordinate a disaster response. That includes FEMA, the Federal Emergency Management Agency.

"We are going to respond to this emergency the way we do other things, such as volcanoes and hurricanes," said Leviticus Lewis, the chief of FEMA's National Response Coordination Branch. Lewis said disaster coordinators are well-versed when it comes to monitoring threats like hurricanes, but less so when it comes to a once-in-a-lifetime event like an asteroid impact.

"If we show emergency managers (asteroid) impact probabilities, they will have no idea," Lewis said. "To date, our goal has been general education on the subject."

An inbound asteroid's exact impact location will be hard to predict, with models being refined right up until the last minute. Even harder to predict will be the public's reaction, since the Internet will allow the entire world to follow along closely.

"You can't hide it," said Johnson. "The information will be instantly out."

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