Success! NASA's DART Redirects Asteroid in 'Watershed Moment for Humanity'

In a test of planetary protection, the spacecraft knocked space rock Dimorphos off course.

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Eric Mack
3 min read
Didymos and Dimorphos as bright white lights

Didymos and Dimorphos as bright white lights after impact.


NASA has succeeded in changing the orbit of asteroid Dimorphos. NASA crashed its Double Asteroid Redirection Test spacecraft, aka DART, into Dimorphos a few weeks ago to test one possible method of protecting Earth from a dangerous body on a collision course with our planet. 

"This is a watershed moment for planetary defense and a watershed moment for humanity," NASA administrator Bill Nelson said while confirming the asteroid redirect during a press conference Tuesday. 

To be clear, this was only a test of one potential defense method, called "deflection by kinetic impactor," that doesn't require nuclear weapons or celebrities on a suicide mission a la popular Hollywood movies like 1998's Armageddon. Dimorphos, which is actually a moonlet orbiting the larger asteroid Didymos, doesn't pose an actual threat to Earth. In fact, no known asteroids or near-Earth objects are considered to be a threat to humanity, but there are still plenty of space rocks and comets out there yet to be discovered or tracked by astronomers. 

Watch this: DART Explained: First Asteroid Crash Images

DART's impact with Dimorphos on Sept. 26 appears to have reduced the time it takes the moonlet to orbit Didymos by 32 minutes, from 11 hours and 55 minutes to 11 hours and 23 minutes, with a margin of uncertainty of about two minutes. NASA had hoped DART would alter the orbital period by at least 73 seconds but expected it could alter the orbit by at least a few minutes and perhaps tens of minutes. So the result is on the high side of the expected possibilities. 

"It looks like the recoil from the ejecta blasted off the surface was a substantial contributor to the overall push given to the asteroid, in addition to the push of the spacecraft directly impacting," said Tom Statler, DART program scientist at NASA headquarters.

Ejecta is a technical term for the dust and debris thrown off into space as a result of the impact. Numerous images taken in the days that followed the impact by telescopes in space and on Earth showed that the ejecta was forming a tail trailing Dimorphos similar to what we see with comets orbiting the sun. 

Nancy Chabot, the DART coordination lead from the Johns Hopkins Applied Physics Laboratory, noted that although the result is considered a resounding success, it still represents only a 4 percent change in the asteroid's orbital period.   

"It just gave it a small nudge, but if you wanted to do this in the future, it could potentially work but you'd want to do it years in advance. Warning time is really key."

Chabot added that the physical location of Dimorphos also changed ever so slightly and the space stone now orbits Didymos a little more tightly than before the impact.   

Scientists on the DART team are continuing to acquire more data from observatories around the world to better understand the dynamics of the impact and its effects. 

Later in the decade, the European Space Agency's Hera project aims to send another spacecraft to conduct detailed surveys of Dimorphos and Didymos, including studying the impact crater left by DART.