DART’s Smashing Success Shows Humanity Can Divert Asteroids

DART’s Smashing Success Shows Humanity Can Divert Asteroids

Nature

NASA confirms that its DART spacecraft nudged the asteroid Dimorphos into a new orbit

After the DART spacecraft ploughed into the asteroid Dimorphos, the Hubble Space Telescope captured images of the ejected plume of dust and debris that streamed for thousands of kilometres behind the space rock. Credit: NASA/ESA/STScI/Hubble

Humans proved for the first time that they can alter the trajectory of a huge rock hurtling through space. NASA has announced that the spacecraft it slammed into an asteroid on 26 September succeeded in altering the space rock’s orbit around another asteroid — with better-than-expected results.

Agency officials had estimated that the Double Asteroid Redirection Test (DART) spacecraft would ‘nudge’ the asteroid Dimorphos closer to its partner, Didymos, and cut its orbit time around that rock by 10-15 minutes. At an 11 October press conference, researchers confirmed that DART in fact cut the orbit time by around 32 minutes.

Although neither asteroid was a threat, the agency tested the maneuver on them to show that humanity can, in principle deflect a space rock headed for Earth.

” This is a watershed point for planetary defense, and a watershed for humanity,” said Bill Nelson, NASA administrator.

Tracking the aftermath

The success of the mission was determined by more than half a dozen telescopes from around the globe. Ground-based optical telescopes cannot resolve Dimorphos and Didymos, which are millions of kilometers away from Earth and only a few hundred meters across. Instead, they see the pair as one point in the nightsky. The telescopes can detect dips in brightness caused by Dimorphos’s cycles behind Didymos. These movements were tracked by observers and compared to the pre-collision orbit times in order to calculate DART’s impact.

Independently a pair of radar facilities, Goldstone Observatory in Fort Irwin (California) and Green Bank Observatory, West Virginia, turned their dishes towards the asteroid pair. Unlike optical telescopes that can only see the asteroids separately, planetary radar allows astronomers to see their positions and estimate Dimorphos orbit time around Didymos.

Both sets of observations agreed that DART’s impact knocked Dimorphos tens of metres closer to its companion and cut its cycle time to around 11 hours and 23 minutes.

Although the orbit reduction is greater than expected, it still falls within scientists’ range of possibilities. Researchers believe the manouevre succeeded because Dimorphos is a loose collection rather than a chunk of rock that would be more difficult to deflect. Researchers also stated that DART hit caused a dramatic orbit change because a lot debris shot out of the asteroid into tails. Each tail was thousands of kilometers long and their recoil likely accentuated DART’s impact.

” We have a lot to do before we can understand what happened,” stated Tom Statler, a DART programme specialist at NASA’s headquarters in Washington DC.

Saving Earth

Scientists continue to monitor the asteroid couplet over the coming months, hoping to learn more about Dimorphos and the impact of DART on the asteroid. With the help of images from LICIACube — the Italian Space Agency’s probe that trailed DART and then flew by to capture the impact — scientists hope to learn more about the properties of the debris ejected.

But the mission’s final postmortem will take at least a decade. Launching in its wake, the European Space Agency’s Hera mission — currently slated for an October 2024 liftoff — should arrive at Dimorphos in 2027, to observe the aftermath of DART’s impact.

For now, the results indicate that the US$330-million DART mission was a success. Researchers say that Earth needs to be protected from future impacts. This requires knowing the properties and locations of dangerous space rocks and being able to act quickly. DART launched in November last year and took about 10 months to hit its target.

If an asteroid were to threaten Earth, Nancy Chabot, a planetary scientist who coordinates DART at Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, stated that a mission would need launch years in advance in order to deflect it safely. “Warning is really key here,” she said, adding that even space rocks larger than the 160-metre-wide Dimorphos might be dealt with given enough planning and time.

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