NASA DART Mission Successfully Smashes Asteroid Into New Path

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NASA took aim at an asteroid last month, and on Tuesday, the space agency announced that its planned 14,000-mile-per-hour collision with an object named Dimorphos made even more of a bull’s-eye shot than expected.

That winning strike was the first of its kind. “We conducted humanity’s first planetary defense test,” said Bill Nelson, the administrator of NASA, during a news conference, “and we showed the world that NASA is serious as a defender of this planet.”

In November 2021, NASA launched the Double Asteroid Redirection Test, or DART, mission, shooting a refrigerator-size spacecraft toward a small asteroid. Scientists had created DART to destroy the spacecraft.

On Sept. 26, the spacecraft smashed into a small asteroid, which defenders of Earth hoped would adjust its orbit. This strategy could protect the planet from incoming asteroids or comets. One small shift in a space rock’s trajectory could, someday, mean one giant sigh of relief for humankind, if it pushes an asteroid off a collision course with Earth.

The mission’s target, Dimorphos, was a diminutive space rock, just more than 500 feet wide. It was and still is harmless, posing no risk to Earth. Before DART’s impact, Dimorphos orbited a larger asteroid called Didymos every 11 hours and 55 minutes. An onboard camera took pictures of the fast-approaching asteroid on the day of the crash. As the spacecraft approached, the asteroid’s surface filled the screen, boulders coming into focus before the transmission cut out. DART and its camera had smashed into the very surface it was showing.

The spacecraft not only connected with Dimorphos, it altered the space rock’s orbit, shortening its trip around a larger asteroid by 32 minutes.

That time shift was exactly what the DART mission aimed to accomplish. Scientists hoped the collision would push Dimorphos closer to Didymos and speed up its orbit, and they have been crunching data and taking more observations of the double-asteroid system to understand how effective this particular defense mechanism was. Scientists, according to Mr. Nelson, would have considered DART a huge success if it had only shortened Dimorphos’s orbit by 10 minutes. The reality — around three times that shift — delighted the team that managed the mission.

“If an Earth-threatening asteroid was discovered and we could see it far enough away, this technique could be used to deflect it,” Mr. Nelson said.

Defending the planet from hazardous space rocks is a newer addition to NASA’s portfolio, and DART was the first mission to test this strategy that could be used in the future. The asteroids that tend to keep astronomers up at night aren’t necessarily the giant planet-killers of science fiction lore, most of which are known and tracked. Instead, they worry about the smaller ones, akin to Dimorphos, that are harder to discover, more numerous and capable of causing great damage to people and property on Earth.

Now that scientists have proven they can alter an asteroid’s movement, they are a step closer to transforming this particular strategy into a method to protect the planet. But translating the science into an operational mission, should the need arise, will take more work.

“It’s exciting that we’ve taken this first step to develop and now to successfully demonstrate asteroid deflection,” said Nancy Chabot, DART coordination lead at the Johns Hopkins Applied Physics Laboratory. The team was happy with the initial results, she continued, “even though there’s still a lot of work to do.”

Scientists tracking the aftermath of the mission studied the wreckage the spacecraft caused from multiple vantages.

The close-up data on the effects of the DART mission came from LICIACube, a shoebox-size satellite built by the Italian Space Agency. Its early images showed sunlight bouncing off a cloud of debris, the size and complexity of which excited astronomers.

“We couldn’t believe our eyes,” said Giorgio Saccoccia, president of the Italian Space Agency, of the data the LICIACube’s two cameras had gathered. The asteroid’s trajectory change was not just a result of the force of the impact: It was also boosted by those debris ejections from the space-object itself.

Other spacecraft, including the James Webb and Hubble Space Telescopes, helped to study how effectively DART bullied Dimorphos onto a different path. Two varieties of data from Earth assisted scientists measuring the asteroid’s orbital change.

The first involved nightly observations from optical telescopes, which watched as Dimorphos passed through the shadow of its parent asteroid, and then threw a shadow of its own on Didymos. The timing of these distant shadows showed the small object circling its larger companion faster than it had before DART smackdown.

Astronomers confirmed this time shift with radar data gathered by the Goldstone Solar System Radar in California and the Green Bank Observatory in West Virginia. “DART clearly had a dramatic effect on poor little Dimorphos,” said Green Bank’s director, Jim Jackson. “These radar measurements will be key to determine just how dramatic the event really was.”

Approximately 40 rubbernecking terrestrial telescopes have also watched the event’s aftermath. Among them was the Southern Astrophysical Research Telescope in Chile, which recorded the wreckage after DART’s impact last month.

“Selfishly, I wanted to take cool pictures,” said Teddy Kareta, an astronomer at the Lowell Observatory, who helped to record the images, “but we mostly wanted to be helpful to the rest of the team.”

The Chilean telescope captured a trail of dust and debris that stretched at least 6,000 miles from where the crash had happened, resembling a comet’s tail.

A Hubble image taken last Saturday showed that the comet-like tail split into two, a separation scientists are still working to interpret. “The learning is going to continue for a long time to come,” said Lori Glaze, director of planetary science at NASA.

In the coming weeks, months and years, astronomers will use instruments on the ground and in space to monitor the first celestial object with an orbit humans have changed. “We have a lot of work ahead of us to really understand what happened,” said Tom Statler, DART program scientist at NASA.

This scrutiny will help reveal how best to protect the planet from deadly asteroids — a kind of intervention that isn’t possible with most natural disasters. DART has proved that scientists can deflect a potentially hazardous asteroid of Dimorphos’s size. But that deflection will require detection: using telescopes on Earth and future space missions to discover asteroids early enough, learning about their nature and hitting them with what we’ve got while they’re relatively far away.

“NASA is trying to be ready for whatever the universe throws at us,” Mr. Nelson said.

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