“The collision of comet Shoemaker-Levy 9 with Jupiter in 1994 sensitized the public to impacts in the solar system,” said Don Yeomans, senior research scientist and manager of the Near-Earth Object Program Office at the Jet Propulsion Laboratory. “Then there were those two dreadful movies around 1998—’Armageddon’ and ‘Deep Impact.’ They sensitized the public. The public contacted their Congressmen, their Congressmen said, ‘NASA, what the heck are you doing about this problem?’”
Thus were born the agency’s efforts to track near-Earth objects.
Yeomans, author of Near-Earth Objects: Finding Them Before They Find Us
, spoke last week at Town Hall Seattle. He must know his stuff; after all, he’s got an asteroid—2956 Yeomans—named after him! Yeomans gave an engaging presentation about the history of rocks slamming into our planet, from the football-sized meteorite that wrecked a New York woman’s Chevy Malibu in 1992 to the 10-kilometer asteroid that nailed us 65 million years ago and snuffed the dinosaurs. He noted that asteroids and comets probably delivered the water and carbon-based materials to the early Earth that allowed life to form, but they could potentially destroy life, too.
Yeomans’ job is to make sure that doesn’t happen. He says an army of professional and amateur observers are tracking thousands of near-Earth objects and feeding the data to JPL.“It’s up to us to compute orbits for all of these objects and run their motions a hundred years into the future to see if any of them make any interesting close-Earth approaches,” Yeomans said. JPL then figures the likelihood of any of these objects actually hitting the Earth.
“If any objects represent a threat we ask for additional observations from the observing community,” Yeomans explained, adding that this helps them pin down an object’s orbit. “As we get more and more data the uncertainties get smaller and smaller and we can run that for a couple of hundred years into the future to see if it is actually going to hit the Earth.”
Yeomans said the probability of something hitting us is not zero.
“There are almost 100 objects on our risk page for which we cannot yet rule out an Earth impact,” he said. “But all of the impact probabilities are very small—one in 10 to the sixth or smaller—so no one should lose sleep over near-Earth objects coming in and taking us by surprise. Still, there are a number of them that we’re keeping an eye on.”
The good news is that there is something we can do about it if we discover an object on a collision course with Earth. In fact, it’s a relatively simple maneuver that we’ve already pulled off: send up a spacecraft and ram it into the thing.
“You could slow it down a millimeter per second and change its orbital period, so in 10 to 20 years when it was predicted to hit the Earth it would miss by a wide margin,” Yeomans said.
His biggest concern is with a comet impact. Comets often aren’t discovered until they reach the orbit of Jupiter. It takes a comet just nine months or so to get from Jupiter to Earth, so if one were headed for us there would be little time to do anything. The good news is that asteroids far outnumber comets, and so a comet impact is a much more remote possibility.
Earlier this month NASA ruled out the chances that the asteroid Apophis will slam into us in 2036, though it will miss Earth by less than 20,000 miles in 2029. Yeomans said they will keep a constant eye out for other near-Earth objects.
“We need to find them before they find us if we are indeed to have a future,” he said.
UPDATE: Speaking of asteroids and Yeomans, Alice’s Astro Info has posted about Asteroid 2012 DA14, which is going to miss us by that much Feb. 15.
Listen to a recording of Yeomans’ talk on the Town Hall Seattle website.
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