The Russia incident was a warning.
On a winter morning in 2013, a meteor the size of a four-story building screamed across the country, exploding near the city of Chelyabinsk and injuring more than 1,600 people amid widespread property damage.
The chunk of rock and iron, which was 60 feet across, served as a violent reminder that Earth, bombarded daily with tons of space-going debris, periodically intersects with large planet killers — and a significant portion of those remain undocumented.
After years of study and discussion, NASA has launched its first effort to spare Earth the kind of calamity that extinguished the dinosaurs, crashing a space probe into an asteroid to alter its speed and course. The Double Asteroid Redirection Test, know as DART, lifted off Nov. 23 local time aboard a SpaceX rocket from California and will cruise for 10 months to a binary asteroid system.
The idea is that if humans have adequate time to react — decades of notice being preferable — enough energy can be transferred into a speeding rock to alter its trajectory and make it miss Earth, avoiding catastrophe up to and including an extinction-level event. (Though a popular subject in science fiction, it’s worth noting that NASA’s current toolkit of asteroid-nudging techniques does not include Morgan Freeman, Bruce Willis or nuclear weapons.)
Given the critical nature of the work, it’s “not a stretch to suggest that DART may be one of the most consequential missions ever undertaken by NASA,” Casey Dreier, an analyst with The Planetary Society, wrote in a memo to members.
“This test is to demonstrate that this technology is mature enough so that it would be ready if an actual asteroid impact threat were detected,” Lindley Johnson, NASA’s planetary defense officer, said at a Nov. 4 news conference.
In September of next year — if all goes as planned — the DART craft will target Dimorphos, the smaller, 530-foot rocky body gravitationally tied to the larger Didymos, which is almost 2,600 feet across. The two rocks travel about 0.6 mile apart, and Dimorphos orbits its larger sibling every 11 hours and 55 minutes, “just like clockwork,” Johnson said.
Traveling at about 15,000 mph, the craft, which weighs 1,344 pounds and is 59 feet across, is to collide head-on with Dimorphos to both slow the rock by a fraction of a second and to adjust its orbital period around the larger asteroid by several minutes.
“It’s all about measuring the momentum transfer: How much momentum do we put into the asteroid by hitting it with the spacecraft?” said Andy Cheng, lead investigator for the mission at Johns Hopkins University’s Applied Physics Laboratory, which built and manages the spacecraft.
Didymos was discovered 25 years ago and has been well-analyzed (insofar as asteroids and comets go). Its course isn’t predicted to meet Earth in the future, but its relatively close trajectory gives scientists a good test platform to observe with telescopes from about 6.8 million miles away.
DART will use laser targeting and other high-resolution technologies to autonomously choose its impact point. As it races toward the rock, the craft’s camera will send images back to Earth. A small cube-satellite released from the main craft before impact will also record images from a safe distance. One big unknown: The smaller body’s surface composition and topography, which are too small to ascertain from Earth.
