DART is NASA’s first Planetary Defense mission. The goal was to test whether this technique, called a kinetic impactor, would deliver enough impact to a fast-moving space rock to significantly throw it off course.
NASA crashes spacecraft into asteroids, passes planetary defense test
It did. Prior to DART’s arrival, Dimorphos orbited Didymos in 11 hours and 55 minutes. Then: blame! The recalculated orbit: 11 hours and 23 minutes.
That 32-minute change in orbital period was at the high end of a range of estimated results, said Lori Glaze, NASA’s director of planetary research. DART exceeded the agency’s minimum criteria for a successful mission by more than 25 times.
“We showed the world that NASA means business as a defender of this planet,” said NASA Administrator Bill Nelson.
The mission “felt like a movie plot” he said. “But that wasn’t Hollywood.”
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Despite the enthusiasm emanating from NASA officials, there is no fully developed system for intercepting asteroids. The key to planetary defense is finding potentially dangerous asteroids well before they cross Earth’s path. Astronomers can calculate if they are on a trajectory to hit the planet.
“You have to know they’re coming,” Glaze said.
The idea of a kinetic impactor is to give a nudge to a dangerous asteroid many years before it is expected to impact Earth. This is not a last minute technique to save the world.
“We really need that advance warning for a technique like this to be effective,” said Nancy Chabot, DART coordinator at Johns Hopkins University’s Applied Physics Laboratory, who handled the mission under a NASA contract.
Large asteroids that could threaten Earth are easy to spot, and their orbits are calculated many decades into the future. But many smaller asteroids in the general size range of Dimorphos with a diameter of about 160 meters are harder to spot.
Asteroids are not identical. Some are hard, solid bodies, while others are “heaps of rubble.” The composition and form of Dimorphos were not known prior to arrival of DART. Only in the final minutes of the mission did the asteroid come into focus. The impact created a stunning ejecta plume, and the asteroid’s dramatic motion came in part from the way it bounced back as boulders and fine particles were flung into space.
The mission was already on the books as an engineering triumph simply due to a successful collision – a direct hit indeed – which was dramatically captured by the spacecraft’s camera in the final moments before impact.
The laws of physics dictated that there had to be some effect. And images taken by a trailing CubeSat provided by the Italian Space Agency and deployed 15 days before DART’s impact showed material hurts into space. Subsequent observations from telescopes on Earth, as well as the Hubble and Webb Space Telescopes, showed a long trail of debris that created a comet-like effect.
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Only on Tuesday, after much analysis, NASA revealed the exact change in the orbit of Dimorphos. Analysis continues, and one question is whether the stone has become shaky.
“We shouldn’t be too eager to say that a test on one asteroid tells us how any other asteroid would behave,” warned NASA program scientist Thomas Statler.
Still, the bottom line is that the DART mission worked exactly as scientists and engineers had hoped.
“Let’s all take a moment to soak this in,” Glaze said. “For the first time ever, mankind has altered the orbit of a planetary body.”
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