Happy Asteroid Day! Unless one of them hits Earth, of course. In that case, not happy at all.
Casual observers might think the risk of a large asteroid strike—the single worst thing that could happen to our planet—has gone away. Thanks to diligent searching by ground-based telescopes over the last 20-plus years, 95 percent of the largest (kilometer or bigger) asteroids in our planetary neighborhood—any of which could end civilization if they struck us—have been identified. None of them is on a collision course. And next year, a spacecraft called DART will try to nudge a small asteroid enough to change its orbit around a bigger asteroid—a tiny first step toward being able to deflect a future attacker.
That doesn’t mean we can rest easy. There are still an estimated 25,000 smaller objects—140 meters and up—that could pack enough of a wallop to destroy a region the size of southern California. Such an impact is estimated to occur roughly once every 100,000 years, but statistics offer only so much comfort. It could happen this afternoon. An asteroid less than half that size hit what is now Arizona 50,000 years ago, whipping up thousand-mile-per-hour winds, flattening an area the size of Kansas City, and leaving behind a mile-wide crater.
In 2005 Congress ordered NASA to identify 90 percent of the 140-meter-and-up, region-destroying rocks, on top of the 1,000 or so kilometer-size objects already found. The deadline was supposed to be 2020. The job is only about 40 percent finished, however, and the pace of discovery is slowing. At the current rate it will take more than 30 years to reach that 90 percent goal.
What’s the holdup? It’s partly a matter of psychology. People, or at least large groups of people, don’t tend to get worked up about a threat so rare that it’s never happened in all of human history. (We can’t even seem to mobilize to address the climate emergency that’s already upon us.)
But there’s another, more mundane, reason for the foot-dragging. It’s been difficult to establish which office within NASA should do the job. To most of us that wouldn’t matter, but in the parochial politics of science funding, it’s been a showstopper. While other, purely scientific asteroid missions have gotten funding, a spacecraft dedicated to searching for asteroids in the name of so-called “planetary defense” was turned down by NASA in 2014.
Now the good news: The Near-Earth Object Surveyor Mission, a descendant of that failed 2014 proposal, appears finally to be on track for a launch in 2026. The mission just got approval this month to go into development, and just as importantly, NASA has requested real funding next year—instead of just study money—to make sure the half-billion-dollar project gets off the ground.
Infrared detectors on the NEO Surveyor spacecraft will be able to find two-thirds of the 140-meter objects in our vicinity within only five years, and combined with other searches, should hit the 90 percent target in 10 years. Unlike ground-based telescopes, the space-based NEO Suveyor can search day and night, and spot objects coming at us from the direction of the sun. It will find plenty of smaller objects, too, giving scientists a much better estimate of the overall risk of impact from objects 50 meters and up over the next century.
After that, advocates for planetary defense would like to see an ongoing program of small space missions, including one to meet up with the asteroid Apophis, which is due to pass very close to Earth (but not hit us) on Friday, April 13, 2029.
Is such a program—an insurance policy for our planet—worth $200 million a year? The public certainly thinks so. Recent polls show that asteroid defense and Earth science rank much higher than sending astronauts to the moon and Mars when people are asked what NASA’s priorities should be. Climate change is arguably the more pressing issue, but there’s a difference. Many government agencies are working on that problem. When it comes to the asteroid threat, there’s really only one major defender right now: NASA.