It doesn't take a Ph.D. to understand the warming and cooling cycle of day and night. During the day, the Sun warms the surface, with temperatures reaching their peak in late afternoon. Some of that heat radiates back into space at night, so temperatures are lowest around dawn.
For some of the smallest bodies in the solar system, that cycle can have a profound effect: It can push them around a little bit, changing their orbits around the Sun. And that makes their orbits tough to predict more than a few decades into the future.
Tens of thousands of asteroids orbit the Sun. Thousands of them range from perhaps a hundred yards to a few miles in diameter. And many of those objects come close to Earth's orbit. If one of the big space rocks were to hit us, it could cause a regional or even global catastrophe.
So astronomers are finding and tracking these objects to see if any are on potential collision courses.
But the predictions break down more than a few decades in advance, largely because of that cycle of day and night. As the asteroid rotates, it radiates heat into space, creating a tiny bit of thrust. Over time, it adds up. A few years ago, for example, astronomers determined that an asteroid that weighs millions of tons had been displaced by about 10 miles in just 12 years. But without a lot more information about the asteroid, it's impossible to predict how that "thrust" will affect its orbit -- even with a Ph.D.
Script by Damond Benningfield, Copyright 2010