“Just from a pure crime-scene sense, a lot of us are curious about that,” Rivkin says. At the same time, bits of the spacecraft’s wreckage might scatter across the asteroid’s surface, but exactly how DART will break apart remains to be seen. The impact will probably leave a crater that could be around 10 metres across. Credit: Ed Whitman/NASA/Johns Hopkins University APLĭepending on the angle at which DART hits the asteroid, it could kick up a small cloud of dust and rubble. Researchers at the Johns Hopkins University Applied Physics Laboratory inspect the DART spacecraft during testing in July.
Other, less cinematically worthy strategies involve altering the asteroid’s trajectory by flying a spacecraft alongside to tug on it using gravitational forces, or smashing into it as the US$330-million DART mission will. Space scientists have floated all sorts of ideas to battle incoming asteroids, the most dramatic of which involves blasting them with nuclear weapons 2. The worry is that some new asteroid could appear, headed directly towards the planet - and that it would be large enough to cause serious consequences when it hits, just as with the asteroid that helped to kill off the dinosaurs and other life on Earth 66 million years ago. NASA has identified more than 27,000 asteroids with trajectories that bring them close to Earth. Small asteroids and asteroid fragments hit Earth all the time, but most of them disintegrate in the atmosphere or fall harmlessly to the ground as meteorites. The impact will occur when the asteroids are 11 million kilometres from Earth. Using the non-threatening pair Dimorphos and Didymos is “a really smart and a safe way to do this first test”, she says. This complicated choreography is meant to test the idea that smashing into an asteroid can give it enough of a nudge to keep it from hitting Earth, says Nancy Chabot, a planetary scientist at JHU-APL who works on the mission. (Dimorphos is named after the Greek for ‘having two forms’, to signal NASA’s intent to change the asteroid’s orbit.) Astronomers using telescopes on Earth will watch Didymos for signs of that orbital change - which would be evident in the way its brightness changes over time, as Dimorphos passes in front of and behind it. The impact should shrink Dimorphos’s orbit so that it circles Didymos at least 73 seconds faster than before. In late September or early October of next year DART will slam headlong into Dimorphos at 6.6 kilometres per second. Dimorphos, the smaller of the two at 160 metres wide, orbits Didymos, which is nearly 5 times larger and is named after the Greek word for ‘twin’.Ĭredit: Adapted from NASA/Johns Hopkins University APL Its target is a pair of asteroids that travel together through space, one orbiting the other as they circle the Sun (see ‘A not-so-gentle nudge’). Launched from California on 23 November, the spacecraft is called the Double Asteroid Redirection Test (DART) 1. “But sometimes your number comes up when you don’t expect it, and it’s good to have an insurance policy.” “The odds of something large enough to be a problem, that we would have to deflect, are pretty slim in our lifetimes,” says Andy Rivkin, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory (JHU-APL) in Laurel, Maryland, which built the spacecraft for NASA.
But researchers want to see whether they can change its trajectory, long before they might need to use such a strategy to deflect a truly dangerous asteroid. The asteroid that NASA is smashing into, called Dimorphos, is not a threat to Earth. Rather than being a catastrophic error, however, it will be the first test of a way to protect Earth from killer asteroids. NASA has just launched a multimillion-dollar spacecraft - to slam into an asteroid.
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