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(Inside Science) — Science fiction books and films have frequently featured the threat of a giant asteroid colliding with our planet and making humans go the way of the dinosaurs. But smaller space rocks also pose threats, and they tend to be harder to spot in advance.
A massive asteroid on a collision course would sail through our atmosphere and explosively burst in the air or crater the ground. Its invasion would initiate blasts of fire and thermal radiation, and likely cause numerous casualties. Even asteroids falling into the ocean could drive tsunamis or earthquakes — and even create undersea craters.
“It will be the first-ever asteroid deflection test,” said Megan Bruck Syal, a physicist at Lawrence Livermore National Laboratory in California and member of the DART team. She points out that there could be tens of thousands of asteroids as big as DART’s target, and the majority of them haven’t been discovered, let alone tracked, yet.
Bruck Syal and other experts presented their research at a conference dedicated to “planetary defense” near Washington, D.C., last week. It even included presentations about how space law applies and about the risks of violent conflict if deflection missions like DART don’t go according to plan.
Didymos’ moonlet matches the size of typical asteroids that could be especially hazardous to Earth. “As you get smaller, there are many more asteroids, but as they get smaller, they carry less energy,” said Donovan Mathias, an aerospace engineer at NASA Ames in Mountain View, California. Based on his team’s models, asteroids between 100 and 200 meters across have the highest probability of striking the Earth and causing substantial damage. Smaller asteroids are more likely to break up into mostly harmless pieces and burn up in the atmosphere, while larger ones are much rarer and easier to find and track.
How the impact plays out and how much momentum DART transfers to the asteroid depends on lots of factors, including the asteroid’s strength and internal structure. “We’re trying to anticipate how much we can actually deflect the Didymos asteroid, and that’s quite challenging because we don’t know what the asteroid is made of,” said Sabina Raducan, a planetary scientist at Imperial College London who has been simulating the impact scenario. “We want to have a very weak, less porous body,” she said, since a hard rock would hardly budge and something that absorbs the impact would defeat the purpose of the collision, too.
In the case of a real-life killer asteroid, people may only get only one shot to deflect it, so there’s plenty of pressure to get the math right. There’s also a chance that throwing a spacecraft at the asteroid won’t be enough. “You’d have to push on it so hard that it would start to come apart,” Bruck Syal said.
Then people would consider blowing up the asteroid and scattering the fragments. Like in the movies, in a last-ditch effort, scientists might actually have to deploy nuclear weapons. “But the more warning time you have, the better,” she said.
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