NASA smashes into an asteroid, completing a mission to save a future day
By Kenneth Chang
It’s the plot point for more than one Hollywood blockbuster: A rogue asteroid is hurtling toward Earth, threatening tsunamis, mass destruction and the death of every human on the planet.
Humanity has one shot to save itself with brave, self-sacrificing heroes piloting a spacecraft into the cosmos to destroy the asteroid.
But that’s the movies. On Monday evening, NASA showed what the reality would be like.
There was an asteroid, but it wasn’t threatening Earth. And there was a spacecraft, relying solely on sophisticated technology. The human heroes of the mission were actually at a physics and engineering lab between Baltimore and Washington, D.C.
And there was a collision. In this case it was the final act of the Double Asteroid Redirection Test, or DART, a spacecraft that launched in November and then raced around the sun for 10 months as it pursued its target — a small space rock, Dimorphos, 7 million miles from Earth.
“For the first time, humanity has demonstrated the ability to autonomously target and alter the orbit of a celestial object,” Ralph Semmel, director of the Johns Hopkins University Applied Physics Laboratory, said during a news conference after the crash. The laboratory managed the mission for NASA.
Hitting an asteroid with a high-speed projectile nudges its orbit. For an asteroid headed toward Earth, that could be enough to change a direct hit to a near miss.
In its last moments, the spacecraft sent back a series of photographs of the asteroid, Dimorphos, as it approached at more than 14,000 mph.
DART had spotted Dimorphos only about an hour earlier, as a dot of light. Then, the pile of celestial rubble grew bigger and bigger, until the picture of the asteroid’s surface strewn with boulders filled the screen. The mission’s engineers were on their feet, cheering.
“Normally, losing signal from the spacecraft is a very bad thing,” Semmel said. “But in this case, it was the ideal outcome.”
There was one more partial image, but the data never made it back to Earth. DART had smashed into the asteroid.
“Wow, that was amazing, wasn’t it?” Nancy Chabot, a planetary scientist at the laboratory who works on the mission, said during the NASA webcast.
The growing focus on planetary defense can be in seen in a number of initiatives that NASA and congressional appropriators have sponsored. One is the Vera Rubin Observatory, a new telescope in Chile that is financed by the United States and will systematically scan the night sky and find thousands of potentially hazardous asteroids. Another is the NEO Surveyor, a space-based telescope that NASA is working to build. It too will find many hazardous asteroids, including some that are hard to spot from Earth.
If any of those asteroids turn out to be on a collision course with Earth, the DART mission shows that deflecting them is a realistic possibility.
For the engineers on the mission, operated by the Johns Hopkins University Applied Physics Laboratory, the impact, at 7:14 p.m. Eastern time, marked the end of their work. The spacecraft, operating autonomously for the last four hours of its existence, successfully locked on Dimorphos.
That is even more impressive because DART’s camera spotted Dimorphos for the first time a little more than an hour before impact. Dimorphos orbits a larger asteroid, Didymos, and until then, the smaller asteroid was lost in the glare of the larger object. DART’s navigation system then shifted its gaze toward the smaller asteroid.
Up until five minutes before impact, mission controllers could have intervened if something had gone wrong. But they did not have to make any adjustments.
During the last five minutes, the people in the control room were spectators, too, like everyone watching the stream of photographs of Dimorphos. And then it was over. Initial analysis indicated that the spacecraft hit within about 50 feet of the target center.
“I definitely feel relieved,” said Elena Adams, the mission systems engineer. “And it is absolutely wonderful to do something this amazing. And we are so excited to be done.”
For asteroid scientists, their work is just beginning.
By design, the crash occurred when the asteroids were fairly close to Earth.
That allowed telescopes on Earth to get a good look. About 40 of them were pointed at Didymos and Dimorphos, according to NASA and the mission’s managers. So were the Hubble and James Webb space telescopes as was the camera on Lucy, another NASA spacecraft. The LICIACube, a spacecraft about the size of a shoe box built by the Italian Space Agency, trailed DART to take photographs of the impact and the plume of debris. Its trajectory was shifted to the side so that it did not also crash into the asteroid.
“There’s the rest of us that are really eagerly anticipating the impacts so that we can take our science and run with it,” said Cristina Thomas, a professor of astronomy and planetary science at Northern Arizona University and lead of the observations working group for the mission. “It’s going to be so great and such an exciting once-in-a-lifetime event that we are throwing everything that we have at it.”
Over the coming days and weeks, Thomas and other astronomers will be sifting through the data and the images to figure out what DART did to Dimorphos. The key measurement will be how much the smaller asteroid, which had been orbiting Didymos every 11 hours, 55 minutes, has sped up. That will reflect how much momentum the spacecraft imparted to the asteroid, causing it to move closer to Didymos. The change is expected to be about 1%, or about seven minutes.
The impact could have given Dimorphos an even bigger push if the space rock was a loosely held together pile of rubble. The crash of DART would have created a deep crater and sent a shower of debris flying into space. That cascade of material would have acted like the thrust of a rocket engine pushing against the asteroid.
Astronomers are looking to see if there is a brightening of the Didymos-Dimorphos system from sunlight reflecting off the debris plume. Analyzing the specific colors of light could reveal details about the composition of Dimorphos.
More detailed study will come years later when Hera, a spacecraft being built by the European Space Agency, arrives to take a close look at the two asteroids, especially the scar made by DART. Scientists estimate that there should be a crater 30 feet to 60 feet wide.
The asteroid pair takes two years to go around the sun, and part of the orbit crosses Earth’s. But there is no danger of either asteroid hitting Earth anytime soon, and the impact had no chance of knocking it into Earth’s path.
Still, with a successful demonstration that an asteroid can be deflected, “I think that earthlings should sleep better,” Adams said. “Definitely I will.”