Is an asteroid on the way?

Forrest M. Mims III

Readers sometimes ask if there is a chance an asteroid can strike the earth.

The short answer is yes. That's because Earth and hundreds of asteroids share some of the same space as we all orbit around the sun.

The moons and planets in our solar system that have a rocky surface are pockmarked by craters caused by impacts of countless asteroids. Earth, too, has been struck by many asteroids. But Earth is such a dynamic and changing planet that evidence of most of its craters has long ago eroded away.

Nevertheless, there are some large impact craters on our planet, and one of the most dramatic is almost in our back yard. It's Arizona's Barringer Meteor Crater, and it's well worth a visit should you ever plan a trip to Arizona.

The huge crater is nearly a mile across. The object that created it is believed to have been about 46 meters (150 feet) in diameter. It was made primarily of iron, and it weighed around 300,000 tons.

Someday our planet may again be struck by an object as large, or even much larger, than the one that formed the Barringer Meteor Crater. If the object is more than half a mile across when it enters the atmosphere, it could cause massive devastation should it strike land.

Some two-thirds of our planet is covered by water, so a water impact is more likely. Should that occur, the resulting tsunami would dwarf the ones created after the giant Christmas Day Indian Ocean earthquake.

Scientists are very aware of the asteroid hazard, and there are various programs that keep very close track of known asteroids and search for new ones.

Currently, the only asteroid known to be on schedule for a close encounter with earth is named 2004 MN4. According to the latest projection from NASA's Near Earth Object Program Office, on April 13, 2029, 2004 MN4 will pass within about 20,000 miles of Earth.

This is less than 10 percent of the distance to the moon! It's closer than geosynchronous TV and weather satellites!

But it's not close enough to cause any damage. Instead, it will appear as a point of light moving rapidly across the night sky.

Forrest M. Mims III and his science are featured online at www.forrestmims.org.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.