A spacecraft that plowed into a small, harmless asteroid millions of miles from Earth succeeded in shifting the orbit of the space rock, Nasa said on Tuesday, announcing the results of its first such test.
The US space agency strategically launched the Double Asteroid Redirection Test (Dart) spacecraft into the path of the asteroid, thereby throwing it off course.
Nasa hopes to be able to deflect any asteroid or comet that comes to pose a real threat to Earth.
The Nasa administrator, the former astronaut and Democratic Florida senator Bill Nelson, said: “We showed the world that Nasa is serious as a defender of this planet.”
Lori Glaze, director of Nasa’s planetary division, said: “Let’s all just take a moment to soak this in. We’re all here this afternoon because for the first time ever, humanity has changed the orbit of a planetary body.”
“I am absolutely thrilled about today’s announcement of the orbital period change due to the Dart impact,” said Cristina Thomas, Dart’s principal investigator.
“I am constantly impressed by this team and the phenomenal observations that they were able to collect in the two weeks since the impact. Our team has been preparing for these observations for years as we worked to understand the pre-impact orbital period and this result is a testament to how prepared we were for this moment.”
Two famous Nasa telescopes, Webb and Hubble, captured the moment the spacecraft collided with the moonlet asteroid on 26 September. It took days of observation to determine how much the impact altered the path of the 525ft asteroid around its companion, a much bigger rock.
The observations revealed that Dart’s impact altered the orbit of Dimorphos around the larger Didymos asteroid by about 32 minutes, shortening the 11 hour and 55-minute orbit to 11 hours and 23 minutes. Before the collision, Nasa officials said that a change in the orbit of 73 seconds or more would be considered a success.
Professor Colin Snodgrass, an astronomer and member of the Dart mission science team at Edinburgh University, said the next step was to work out what the change in orbit says about the internal structure of Dimorphos. “There was a very large range in predictions on what might possibly happen precisely because we don’t know that much about the interior structure of asteroids,” he said.
“Now that we have the result of the experiment, we can work backwards to see what range of possible starting points give us the sort of period change we saw,” he added. “Since the full range of pre-impact predictions went, in extreme cases, from “nothing happens” to “completely destroy Dimorphos”, the half-hour change is not outside of predictions.”
In a statement following the test, Nasa said Dart “intentionally crashed into Dimorphos, the asteroid moonlet in the double-asteroid system of Didymos. It was the world’s first test of the kinetic impact mitigation technique, using a spacecraft to deflect an asteroid that poses no threat to Earth, and modifying the object’s orbit.
“Dart is a test for defending Earth against potential asteroid or comet hazards,” the space agency said.
Dart altered the orbit of the Dimorphos asteroid by 32 minutes. Glaze said the minimum requirement for changing the orbital period was “really only 73 seconds”.
Glaze noted, however, that if a future asteroid threatens Earth, work on deflection would need to start far in advance: with the Dart mission having caused only a 4.5% change in orbit time, “the more time we have for that little nudge … the better off we are”.
The Dart spacecraft, launched last year and roughly the size of a vending machine, was destroyed when it slammed into the asteroid 7m miles away, at 14,000mph, Nasa said.
On Tuesday, public figures were quick to congratulate Nasa on the success of the test, which cost $325m.
In a tweet, the vice-president, Kamala Harris, said: “Congratulations to the team at Nasa for successfully altering the orbit of an asteroid. The Dart mission marks the first time humans have changed the motion of a celestial body in space, demonstrating technology that could one day be used to protect Earth.”
The scientist and educator Bill Nye said: “We’re celebrating … because a mission like this could save the world.”