NASA and the European Space Agency (ESA) announced this week updated plans to launch a spacecraft toward an asteroid in order to knock it off course; a test plan that may come in handy someday should a space rock seriously threaten the planet (again).
As EarthSky reports, the Double Asteroid Redirection Test (DART) mission will launch in 2021, reach its target in 2022, and will then be followed up sometime later with a second mission to see if it worked.
Didymus And Didymoon
Way out there in space, millions of miles away, is a binary asteroid system. The larger of the two space rocks is Didymus, at about 800 feet wide. It’s accompanied by a “moon” of sorts, the 525-foot-wide “Didymoon.” The smaller body is NASA’s target.
Why Didymoon? Its size makes it perfect for the test. Roughly equivalent in size to Egypt’s Great Pyramid of Giza, Didymoon is the size of asteroid that gives NASA the most concern. Smaller ones generally burn up in the atmosphere before causing much damage. Larger ones are easier for NASA to track. But small-to-medium-sized rocks like Didymoon can slip past detection and then not show up until it’s too late – like the one that exploded over Chelyabinsk, Russia, in 2013, injuring over 1,000 people and causing hundreds of millions of dollars in property damage.
RT @ESA_Tech: @elakdawalla an ESA colleague made a modification of your Planetary Society diagram to help communicate the small size of Didymos's Didymoon – would we be okay to use publicly with appropriate credit? pic.twitter.com/xGX59eSDml
— ruimtevaart (@ruimtevaart) January 30, 2019
Neither Didymus nor Didymoon are in any way a threat to Earth. They’re both too far away and on a course that takes them nowhere near us, which means they make a perfect target for this test.
What’s Going To Happen?
If all goes well, a probe will slam into the asteroid at approximately four miles per second, according to Thrillist, and then knock it off of its trajectory and, hopefully anyway, out of harm’s way.
Plans to knock an asteroid off course via the DART program have actually been in place for a while now, but this week’s announcement reveals that the ESA is partnering with NASA for a follow-up test. A second spacecraft, named Hera, will visit Didymoon sometime later to investigate the crater made by the DART mission and to calculate its current trajectory to see if it worked.
Why Not Just Nuke It?
Here’s the problem with destroying an asteroid in space, whether with nuclear weapons or otherwise. If you have, say, one million kilograms of solid asteroid heading your way, and you blast it to smithereens, you now have one million kilograms of smaller asteroids, in the form of rocks and dust and debris, still heading your way. The Earth will still absorb all of the impact of the mass of the asteroid, and it will just be spread over a larger area and divided by several million times. That’s not a good thing.
To that end, the space community has collectively decided that knocking a potential killer asteroid off course is the best way to go. With any luck, the DART mission will prove that it’s possible.