Um, About That Asteroid That Wasn't Going to Hit Us...S

For a while there in 2004, the newly-discovered asteroid 99942 Apophis looked like it had Earth's number. Then scientists crunched some numbers, and the odds of a terrestrial bullseye dropped to 1 in 45,000, where they stand today. Sort of. It turns out that there are a few things we still don't know about the orbit of Apophis, which could change its projected course by millions of miles, according to an article yesterday in New Scientist. Are we going to get slammed by the 270-meter long hunk of rock? We probably won't know for sure until we get a closer look at its close-ish Earth flyby in 2013.

We already know that Apophis is due for a close pass by Earth in 2029, and if things go just right (or wrong), April 13, 2036 could be a very bad day for us.

But before we go running for cover, there's a lot we still need to figure out about this mean-looking space rock. From the article:

One problem, says [Jon Giorgini of NASA's Near-Earth Object Program], is that our calculations do not include effects arising from the fact that Earth is not a perfect sphere. This slightly alters its gravitational field and could make a difference to the asteroid's path when it swings close to Earth.

Yet the most powerful steer could come from the way the sunlit asteroid radiates heat, says Giorgini. Radiation gives rise to a small thrust, and since warmer areas of the asteroid radiate more than cooler ones, there is a net force on the asteroid. This phenomenon - the Yarkovsky effect - means our calculations of Apophis's path could be out by millions of kilometres, according to Giorgini, who will present his results at the Asteroid, Comets, and Meteors conference in Baltimore, Maryland, on 17 July.

Of course it's possible that refining the calculations will cause the odds to drop beyond their already minuscule levels. But it's also possible that in a couple of years we are going to be *very* interested in former astronaut Rusty Schweickart's idea of a asteroid-avoidance gravity tractor that just the other week barely scraped up $50,000 of funding.

Source: New Scientist