A spacecraft named Dart zeroed in on the asteroid, intent on slamming it head-on at 14,000 mph. The impact should be just enough to nudge the asteroid into a slightly tighter orbit around its companion space rock — demonstrating that if a killer asteroid ever heads our way, we’d stand a fighting chance of diverting it.
Cameras and telescopes will watch the crash, but it will take days or even weeks to find out if it actually changed the orbit.
The $325 million planetary defense test began with Dart’s launch last fall.
The asteroid with the bull’s-eye on it is Dimorphos, about 7 million miles from Earth. It is actually the puny sidekick of a 2,500-foot asteroid named Didymos, Greek for twin. Discovered in 1996, Didymos is spinning so fast that scientists believe it flung off material that eventually formed a moonlet. Dimorphos — roughly 525 feet across — orbits its parent body at a distance of less than a mile.
This really is about asteroid deflection, not disruption. This isn’t going to blow up the asteroid. It isn’t going to put it into lots of pieces. Rather, the impact will dig out a crater tens of yards in size and hurl some 2 million pounds of rocks and dirt into space.
The Johns Hopkins lab took a minimalist approach in developing Dart — short for Double Asteroid Redirection Test — given that it’s essentially a battering ram and faces sure destruction. It has a single instrument: a camera used for navigating, targeting and chronicling the final action. Believed to be essentially a rubble pile, Dimorphos will emerge as a point of light an hour before impact, looming larger and larger in the camera images beamed back to Earth. The spacecraft’s navigation is designed to distinguish between the two asteroids and, in the final 50 minutes, target the smaller one.
The size of a small vending machine at 1,260 pounds, the spacecraft will slam into roughly 11 billion pounds of asteroid.
Little Dimorphos completes a lap around big Didymos every 11 hours and 55 minutes. The impact by Dart should shave about 10 minutes off that. Although the strike itself should be immediately apparent, it could take a few weeks or more to verify the moonlet’s tweaked orbit. Cameras on Dart and a mini tagalong satellite will capture the collision up close. Telescopes on all seven continents, along with the Hubble and Webb space telescopes and NASA’s asteroid-hunting Lucy spacecraft, may see a bright flash as Dart smacks Dimorphos and sends streams of rock and dirt cascading into space. The observatories will track the pair of asteroids as they circle the sun, to see if Dart altered Dimorphos’ orbit. In 2024, a European spacecraft named Hera will retrace Dart’s journey to measure the impact results.
Although the intended nudge should change the moonlet’s position only slightly, that will add up to a major shift over time. The experiment will provide valuable insight.
Planet Earth is on an asteroid-chasing roll. NASA has close to a pound of rubble collected from asteroid Bennu headed to Earth. The stash should arrive next September. Japan was the first to retrieve asteroid samples, accomplishing the feat twice. China hopes to follow suit with a mission launching in 2025. NASA’s Lucy spacecraft, meanwhile, is headed to asteroids near Jupiter, after launching last year. Another spacecraft, Near-Earth Asteroid Scout, is loaded into NASA’s new moon rocket awaiting liftoff; it will use a solar sail to fly past a space rock that’s less than 60 feet next year. In the next few years, NASA also plans to launch a census-taking telescope to identify hard-to-find asteroids that could pose risks. One asteroid mission is grounded while an independent review board weighs its future. NASA’s Psyche spacecraft should have launched this year to a metal-rich asteroid between Mars and Jupiter, but the team couldn’t test the flight software in time.