The US space agency’s Double Asteroid Redirection Test (Dart) craft hit its target at 12.14am (BST) this morning (27 September) after 10 months flying in space.
Controlled by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, the mission was NASA’s first attempt to move an asteroid. Dart’s impact with the asteroid “demonstrates a viable mitigation technique for protecting the planet from an Earthbound asteroid or comet, if one were discovered,” the agency said.
“At its core, Dart represents an unprecedented success for planetary defence, but it is also a mission of unity with a real benefit for all humanity,” said NASA administrator Bill Nelson. “As NASA studies the cosmos and our home planet, we’re also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth.”
Dart targeted the asteroid moonlet Dimorphos, a small body just 160m in diameter. It orbits a larger 780m asteroid called Didymos. Neither asteroid poses a threat to Earth.
The mission’s one-way trip confirmed NASA can successfully navigate a spacecraft to intentionally collide with an asteroid to deflect it, a technique known as kinetic impact.
The mission’s investigation team will now observe Dimorphos using ground-based telescopes to confirm that Dart’s impact altered the asteroid’s orbit around Didymos. Researchers expect the impact to shorten Dimorphos’ orbit by about 1%. Precisely measuring how much the asteroid was deflected is one of the primary purposes of the full-scale test.
“Planetary defence is a globally unifying effort that affects everyone living on Earth,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA headquarters in Washington. “Now we know we can aim a spacecraft with the precision needed to impact even a small body in space. Just a small change in its speed is all we need to make a significant difference in the path an asteroid travels.”
The spacecraft’s sole instrument, the Didymos Reconnaissance and Asteroid Camera for Optical navigation (Draco), together with a sophisticated guidance, navigation and control system that works in tandem with Small-body Manoeuvring Autonomous Real Time Navigation (Smart Nav) algorithms, enabled Dart to identify and distinguish between the two asteroids, targeting the smaller body.
These systems guided the 570kg box-shaped spacecraft through the final 90,000km of space into Dimorphos, intentionally crashing into it to slightly slow the asteroid’s orbital speed. Draco’s final images, obtained by the spacecraft seconds before impact and sent to Earth already, revealed the surface of Dimorphos in close-up detail.
The last complete image of Dimorphos, taken by the Draco imager 12km from the asteroid and two seconds before impact (Credit: NASA/ Johns Hopkins APL)
A companion spacecraft from the Italian Space Agency, the Light Italian CubeSat for Imaging of Asteroids (LICIACube), deployed from the spacecraft 15 days before impact to capture images of the crash and the asteroid’s resulting cloud of ejected material. Researchers hope the images, which will be sent to Earth over the coming weeks, will help them characterise the effectiveness of kinetic impact in deflecting an asteroid.
“Dart’s success provides a significant addition to the essential toolbox we must have to protect Earth from a devastating impact by an asteroid,” said Lindley Johnson, NASA’s planetary defence officer. “This demonstrates we are no longer powerless to prevent this type of natural disaster. Coupled with enhanced capabilities to accelerate finding the remaining hazardous asteroid population by our next planetary defence mission, the Near-Earth Object (Neo) Surveyor, a Dart successor could provide what we need to save the day.”
With the asteroid pair within 11m km of Earth, a global team is using dozens of telescopes stationed around the world and in space to observe the asteroid system. Over the coming weeks, they will characterise the ‘ejecta’ produced and precisely measure Dimorphos’ orbital change to determine how effectively Dart deflected the asteroid. The results will help validate and improve computer models critical to predicting the effectiveness of this technique as a reliable method for asteroid deflection.
“This first-of-its-kind mission required incredible preparation and precision, and the team exceeded expectations on all counts,” said APL director Ralph Semmel. “Beyond the truly exciting success of the technology demonstration, capabilities based on Dart could one day be used to change the course of an asteroid to protect our planet and preserve life on Earth as we know it.”
Roughly four years from now, the European Space Agency’s Hera project will conduct detailed surveys of both Dimorphos and Didymos, with a particular focus on the crater left by Dart’s collision and a precise measurement of Dimorphos’ mass.
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