An asteroid portrayed to be passing in front of the blue-green Earth and the moon.
An asteroid passes by Earth in this ESA illustration. Credit: ESA/P. Carril

“Foust Forward” appears in every issue of SpaceNews magazine. This column ran in the March 25, 2019 issue.

In December, a small asteroid exploded in the Earth’s atmosphere in the most powerful event since the February 2013 explosion above Chelyabinsk, Russia. And no one noticed, at least at first.

The event only recently came to light when it appeared on a list of fireballs maintained by the Center for Near Earth Object Studies at the Jet Propulsion Laboratory. The fireball was detected by sensors on U.S. military satellites used for missile warning, and added to the list when it became clear it was natural in origin.

Those sensors estimated the explosion to be equivalent to 175 kilotons of TNT, about 40 percent the size of the Chelyabinsk explosion that caused millions of dollars in damage to the city, and bigger than anything else tracked in the last three decades. That explosion, though, took place more than 20 kilometers above the Bering Sea, off the coast of Siberia. Researchers later found images of the fireball by a Japanese weather satellite and a NASA Earth science satellite, showing it taking place high above clouds that would have obscured it from anyone below.

While the fireball might not have been as stunning — or, fortunately, as damaging — as Chelyabinsk, it provided another reminder of the hazards that near Earth objects, or NEOs, pose to the Earth. The good news is that NASA’s efforts to track, study and prepare for such hazards is more robust than ever.

NASA’s planetary defense program, part of the agency’s planetary science division, received $150 million in the final fiscal year 2019 spending bill in February. The administration’s fiscal year 2020 budget request, issued March 11, also seeks $150 million for planetary defense.

That’s a far cry from early this decade, when NASA spent just a few million dollars a year on NEO searches using ground-based telescopes. It initially got a funding boost when NASA pursued the Asteroid Redirect Mission, in part because of the need for expanded searches for asteroids that the proposed spacecraft could visit. The funding remained in place, though, even after ARM faded away.

A big reason for the current high level of funding is the development of another spacecraft mission, the Double Asteroid Redirection Test (DART), slated for launch in 2021. It will arrive at the near Earth asteroid Didymos in October 2022 — and promptly slam into a small moon, about 150 meters across, orbiting the asteroid. Observation of the resulting deflection of the moon’s orbit around Didymos will help scientists refine plans for how such “kinetic impactors” could be used if an asteroid was threatening to collide with Earth.

If DART was a one-time mission, funding for the planetary defense program would likely start dropping in 2021 as the spacecraft is completed and launched. But advocates for the program hope to sustain that level of funding, if not increase it, with additional missions.

The most likely mission after DART is NEOCam, a space-based observatory that’s been studied for years to more efficiently search for NEOs than telescopes on the ground. Its supporters think that, with maturation of the technology for its main camera, it could be ready to proceed in the next few years as part of the planetary defense program. Another idea being considered is a mission to the asteroid Apophis when it makes a very close approach to Earth in 2029.

For now, there seems to be little objection to the growing size of the planetary defense program at NASA. “One of the questions I always get is, ‘Why is NASA doing planetary defense?’” said Lori Glaze, acting director of NASA’s planetary science division, during a workshop about the program at the recent Lunar and Planetary Science Conference in Texas. “From my perspective, who else would you want doing that?”

While other agencies support NASA, particularly in developing plans to deal with potential impacts, it remains the lead agency for planetary defense. And, as the Bering Sea fireball demonstrates, there’s a lot out there to defend against.


Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. His Foust Forward column appears in every issue of the magazine.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...