NASA’s DART spacecraft struck the moonless asteroid Dimorphos Monday in a historic test of humanity’s ability to prevent a cosmic object from destroying life on Earth.
“Impact confirmed for the world’s first planetary defense test mission,” said a graphic in the space agency’s livestream, as engineers and scientists erupted in cheers.
The Double Asteroid Redirection Test (DART) spacecraft launched from California last November and is rapidly closing in on its destination at about 14,000 miles per hour.
“Today we are taking a giant step in planetary defense,” NASA chief Bill Nelson said in a video statement ahead of the planned impact.
Of course, neither the asteroid moon Dimorphos nor its orbiting big brother Didymos pose a threat as the pair orbits the Sun and flies by about 11.2 million kilometers from Earth at their current “minimum” position.
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However, NASA has deemed it important to conduct the experiment before an actual need is discovered.
If all goes according to plan, the impact between the machine-sized spacecraft and the 530-foot (160-meter) asteroid — roughly the size of an Egyptian pyramid — should take place at 7:14 p.m. Eastern time (11:14 p.m. GMT), as seen on a live NASA broadcast.
By hitting Dimorphos head-on, NASA hopes to put him in a smaller orbit, cutting the time it takes to orbit Didymos by 10 minutes, which is currently 11 hours and 55 minutes — a change that will be reflected in to be detected by ground telescopes in days or weeks to come.
The proof-of-concept experiment will make a reality what has only been attempted in science fiction so far – especially in films like Armageddon and Don’t look up.
As the craft proceeds autonomously like a self-guided rocket for the final four hours of the mission, its imager begins beaming down the very first images of Dimorphos before slamming onto its surface.
“What we are looking for is signal loss. And what we’re celebrating is a loss of the spacecraft,” said Bobby Braun of the Johns Hopkins Applied Physics Laboratory.
Minutes later, a toaster-sized satellite called LICIACube, which separated from DART a few weeks ago, will pass close by to capture images of the collision and ejecta — the pulverized rock thrown off by the impact.
The images from LICIACube will be sent back in the coming weeks and months. Watch the event too: a number of telescopes, both on Earth and in space – including the recently commissioned James Webb – that may be able to see a brightening dust cloud.
The mission has excited the global astronomy community, with more than three dozen ground-based telescopes participating, including optical, radio and radar telescopes.
“There are many of them, and it’s incredibly exciting to have lost track,” said DART mission planetary astronomer Christina Thomas.
Eventually, a full picture of what the system looks like will be revealed when a European Space Agency mission called Hera arrives in four years’ time to probe Dimorphos’ surface and measure its mass, which scientists can only guess at this time.
To be prepared
Very few of the billions of asteroids and comets in our solar system are considered potentially dangerous to our planet, and none are expected in the next hundred or so years.
But wait long enough and it will happen.
We know this from geological records — for example, the six-mile-wide asteroid Chicxulub struck Earth 66 million years ago, plunging the world into a long winter that resulted in the mass extinction of dinosaurs along with 75 percent of all species.
An asteroid the size of Dimorphos, on the other hand, would only have regional effects, like devastating a city, albeit with greater force than any atomic bomb in history.
How much momentum DART imparts to Dimorphos depends on whether the asteroid is solid rock or more of a “garbage heap” of boulders bound by each other’s gravity – a property that is not yet known.
The shape of the asteroid is also unknown — whether it’s more like a dog bone or a diamond, for example — but NASA engineers are confident that DART’s SmartNav guidance system will hit its target.
If it misses, NASA will have another shot in two years, with the spacecraft holding just enough fuel for another pass.
But if successful, the mission will mark the first step towards a world capable of defending itself against a future existential threat.
There’s more to come
Originally released as NASA’s DART spacecraft, it collides with an asteroid in the world’s first planetary defense test mission