Two Close Shaves in Two Days

951 Gaspra

Today an asteroid passed by the earth closer than the moon, at a distance of about 217,000 miles. You read about them every once in a while, but these things zipping by every day! Tomorrow a rock between 7 and 30 yards across will come within 50,000 miles.

NASA's Jet Propulsion Laboratory tracks these Near Earth Objects (NEOs) on a web page anyone can access. Over the next two months more than 80 asteroids will pass by Earth with an average of 40 lunar diameters (9 million miles) at closest approach. That's two or three a day.

Most of them aren't that close -- 9 million miles is a tenth of the distance between the earth and the sun. But that's a lot of junk floating around in space near us.

All of these are too small and dim to be seen with the naked eye. But that doesn't mean they aren't potentially dangerous: five of these 81 asteroids may be as much as a mile across. A strike by an asteroid of that size on earth could kill a lot of people and drastically change the weather.

These asteroids are still being discovered by the hundreds each year. As of March 3rd, JPL was tracking 10,665 NEOs. Even though these asteroids aren't currently on a collision course with earth, we need to keep an eye on them because their orbits can be perturbed by interactions with other asteroids and big planets like Jupiter, which has a tendency to yank asteroids out of the asteroid belt and send them careening across the solar system.

So, no Armageddon this week. But keep your eyes on the skies.