You are here

Moon and Mars

January 22, 2015

A thousand or so large asteroids follow orbits that bring them close to Earth. And once every million years or so, one of these big space rocks rams into our planet, causing widespread devastation.

Big asteroids threaten Mars as well. In fact, Mars is much closer to the inner edge of the asteroid belt, so there are more big rocks whose orbits bring them close to Mars than to Earth. But Mars is smaller than Earth is, and its gravitational pull is weaker, so it doesn’t drag in as many asteroids.

A recent study suggested that Mars also gets hit by one of these large asteroids — roughly two-thirds of a mile across or bigger — once every million years or so.

The study also suggested that Mars is about three times as likely to get hit when it’s farthest from the Sun than when it’s closest. Mars’s orbit is a good bit more lopsided than Earth’s, so the planet’s distance from the Sun varies by almost 30 million miles. The closer proximity to the asteroid belt when Mars is farthest from the Sun should account for some of the higher risk of impact, but not all.

Far from the Sun or close in, though, it seems likely that Mars is a common target for big asteroids.

And Mars is easy to pick out this evening because it’s quite close to the crescent Moon. It looks like a moderately bright yellow-orange star quite close to the left of the Moon. The much brighter planet Venus, the brilliant “evening star,” stands below them.


Script by Damond Benningfield, Copyright 2014

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.