Late Tuesday evening PST (Nov. 23), an unmanned NASA spacecraft is scheduled to launch from California on a 6-million-mile suicide mission to slam into an asteroid named Dimorphos. Unlike in a science fiction movie, Dimorphos is not on course to threaten Earth in any way. But the mission, dubbed the Double Asteroid Redirection Test (DART), is designed to explore strategies that could be used someday to alter the course of asteroids that might, indeed, be on a collision course with us.
“It’s a really clever idea,” said Jonathan McDowell, a staff astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “In 2015, Project Deep Impact slammed a spacecraft into a comet and made a large crater.” But there was no way for astronomers to measure whether it had any effect on the comet’s trajectory.
Dimorphos is a different story, and the ideal target for the DART spacecraft, McDowell told AVweb. Measuring about 525 feet across, Dimorphos orbits around a larger, 2,500-foot-wide asteroid named Didymos, which, in turn, orbits around the sun like Earth does. Still, DART hitting even the smaller asteroid is described as like a golf cart hitting a pyramid, but hitting it at 15,000 miles per hour.
“Astrophysicists look for sensitive ways to measure things,” McDowell said. And astronomers can use imaging to determine if Dimorphos’ orbit around Didymos changes as a result of the impact, and by how much.
As challenging as it may sound for NASA, “Hitting the asteroid is the easy part,” McDowell said. More difficult is assessing the density of the asteroid, and how much that will affect future missions to redirect other asteroids that could be a threat to Earth (even a small asteroid the size of Dimorphos could destroy an entire city). The more solid the asteroid, the more energy from the DART will contribute to changing its course. But a “squishy” (McDowell’s word) asteroid could absorb energy from the collision like a giant sponge, minimizing trajectory change. The spacecraft will send back video to NASA of its final moments before impact, hopefully giving astronomers like McDowell and others a good sense of just how “squishy” Dimorphos is.
All this will play out late next year when DART completes its 6-million-mile journey. And just before reaching Dimorphos, the spacecraft will release a photo pod that will observe from above what NASA hopes will be one hell of a crash.