A NASA spacecraft slammed into the surface of a distant asteroid at 7:14PM ET on Monday night, the climax of the agency’s Double Asteroid Redirection Test (DART).
An hour before impact, the target asteroid, Dimorphos, wasn’t even visible in the images from the spacecraft. In some of the early images sent back to Earth, even Dimorphos’ larger companion Didymos, looked like a single speck against a sea of black. The DART spacecraft was moving at 14,000 miles per hour, and details quickly came into view. Viewers on Earth saw the rough surface of Didymos zip by as the spacecraft cruised autonomously towards Dimorphos. Boulders filled the screen just before it went bright red, indicating a loss of signal — DART had reached its final destination.
Telescopes around the world (and a few in space!) are now turning their attention to the scene of the collision. They’ll be watching to see how much the impact changed the movement of Dimorphos. The crash is part of the first practical planetary defense experiment — a trial to see if humanity might one day be able to redirect the path of an asteroid headed toward our planet.
“We’re embarking on a new era of humankind, an era in which we potentially have the capability to protect ourselves from something like a dangerous hazardous asteroid impact. What an amazing thing. We’ve never had that capability before.“ said Lori Glaze, Director of NASA’s Planetary Science Division, soon after the impact.
To be clear, neither Dimorphos nor Didymos, pose any danger to Earth. No known asteroids pose a significant and immediate threat to our planet. But NASA is playing a long game. Someday in the future, if an asteroid is spotted on a dangerous path, the agency wants us to have options that could let us avert catastrophe.
The option that DART is testing is one of the most direct; if we slam something into an asteroid, will it change how that asteroid moves? Because Dimorphos’ orbit takes it between another asteroid (Didymos) and Earth, researchers will soon have an answer to that question.
Dimorphos is relatively small, so scientists couldn’t actually see the asteroid until just before the collision. But telescopes can see Didymos dimming every time that Dimorphos crosses between it and Earth. This lets researchers know how fast the asteroid is moving. They expect to see Dimorphos’ orbit speed up after the collision, but how closely the asteroid’s behavior will match the computer models remains to be seen.
Before impact, the DART spacecraft released a smaller satellite, the Italian-built LICIACube. This tiny spacecraft followed DART on its way to its doom, taking pictures of the immediate aftermath, which will be sent back to researchers on Earth. Telescopes on seven continents will also focus on the asteroid system, as will the Lucy spacecraft, the James Webb Space Telescope, and the Hubble space telescope. All of them will be monitoring Dimorphos to see if the stadium-sized asteroid’s orbit has changed.