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NASA made history by knocking an asteroid off course. Now, it's publishing the data


Last September, NASA made history by knocking an asteroid off course. A mission called DART crashed a spacecraft the size of a golf cart into an asteroid the size of the Great Pyramid in Egypt. The goal was to test out asteroid deflection, see if it could be used to defend the planet if a big space rock ever threatened Earth. As NPR's Nell Greenfieldboyce reports, astronomers are still watching that asteroid to see how it reacted to getting whacked.

NELL GREENFIELDBOYCE, BYLINE: The asteroid is named Dimorphos. Mission managers at the Johns Hopkins University Applied Physics Laboratory got their first real look at it in the final moments of the mission as the DART spacecraft got closer and closer, sending back images of what turned out to be a gray, egg-shaped asteroid covered with rubble.




GREENFIELDBOYCE: Once the spacecraft went whammo, those images stopped. But telescopes on the ground and in space showed that the impact kicked up a huge cloud of dust and debris.

ANDY CHENG: And it kept getting brighter and brighter and brighter. So it was producing a lot of ejecta.

GREENFIELDBOYCE: Andy Cheng is one of the lead investigators for this mission. He says there was so much rocky material shooting out, the asteroid got an extra kick.

CHENG: The same way that if you fire a gun and you shoot a bullet back that way, the gun kicks back against you. So that's - the recoil force is an extra force that's pushing against the asteroid.

GREENFIELDBOYCE: That force, plus the push from the spacecraft itself, had a real effect on its path through space. Dimorphos orbits another larger asteroid, and the collision changed how long it takes to orbit its bigger buddy, shortening that time by 33 minutes. That's according to a new report in Nature. It's one of five scientific papers in this journal that lay out a detailed picture of what happened in the wake of this experiment. Cheng says asteroid deflection is no longer just some theoretical sci-fi idea.

CHENG: We know this process is really very effective. It's even more effective than a lot of people had originally expected.

GREENFIELDBOYCE: He says in the future, if a dangerous asteroid is headed our way, scientists will have more confidence in their ability to deflect it, even larger asteroids or ones that show up with less warning. After the impact, astronomers watched fascinated as the cloud of debris around Dimorphos evolved into a long comet-like tail. Telescopes can still detect it. Cristina Thomas is an astronomer with Northern Arizona University.

CRISTINA THOMAS: We are still observing, and our observations are going to wrap up in March.

GREENFIELDBOYCE: And next year, the European Space Agency will send out a mission that should take close-up images of the asteroid, revealing what kind of crater might be there, as well as the asteroid's mass, all of which should help astronomers understand even more about how to push asteroids around. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.

Nell Greenfieldboyce is a NPR science correspondent.