ThothWeb - Your Portal to the Unknown - Asteroid may be headed Earth's way in 2036

From a human perspective, Earth-crossing asteroids can have good timing or bad timing. Good timing is when the asteroid and the Earth don't meet. Bad timing is when they do.

Astronomers say that a 1,000-foot diameter asteroid discovered last year may have bad timing. There is a slight possibility that the rock, 99942 Apophis, will hit Earth in 2036 after coming within about 20,000 miles in 2029. A collision could cause regional devastation on a scale far worse than last year's tsunami.

"The most likely thing is that it is not going to be a threat," said Rusty Schweikart, a former Apollo astronaut and chairman of the B612 Foundation, which is concerned about protecting Earth from asteroids. "There's 5,499 chances out of 5,500 that it's going to miss us."

The trouble with Apophis, Schweikart said, is that that one chance cannot yet be ruled out. Better optical and radar observations are needed to determine the asteroid's orbit, but the best measurements cannot be made until 2013.

That creates a different timing problem. If the threat from Apophis cannot be ruled out by then, will there be time to deflect it? Schweikart's group is not sure and has urged NASA to plan a robotic mission to put a radio transponder on the asteroid so that its orbit can be precisely determined. If such a mission takes 10 years to design and execute, it will still give plenty of time to plan and carry out a deflection mission.

NASA has said that planning for a transponder mission can wait till after the more precise measurements are made in 2013.

"I have a very high confidence that we can pinpoint exactly the track it's going to follow," said Andy Dantzler, director of NASA's solar system division. In the unlikely event that in 2013 a transponder mission would still be necessary, there would be enough time for that and a deflection mission, if needed, as well, he added.

Schweikart said that NASA's response was "probably fine." But he added that it made "aggressive assumptions about how good things are going to be, and how much we're going to know."

Edward T. Lu, a current astronaut and a board member of B612, said a transponder mission made sense, given the timeline and the potential risks. "We buy insurance for stuff that's a lot less likely than 1 in 5,500," he said.

Should deflection prove necessary, Lu said, it will have to happen before 2029, so that Apophis will miss a "keyhole" - a region in space only 2,000 feet wide where Earth's gravitational pull will put the asteroid on a collision course. Deflecting it after that, when it would have to miss a much bigger target, Earth, is not technologically possible in so short a time.

Lu and another astronaut, Stanley G. Love, have a proposal for how to go about deflecting the asteroid: by using a spacecraft to tow it, but without a tow line. In a brief paper in Nature, the two describe how such a gravitational tractor, hovering near an asteroid with its engines canted to avoid the exhaust's hitting the surface, can slowly pull it into a different orbit.

The pulling force would only be about one newton, or roughly the amount of force used to hold a full cup of coffee. "But the point is, if you hang out long enough, it can add up to a substantial oomph," Lu said.

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