As we gaze into the night sky, we see only one close neighbor: the Moon. It’s a quarter of a million miles away — millions of miles closer than any other large body. But a lot of little bodies inhabit our region of the solar system. They’re too small to see with our eyes. But they follow orbits that can bring them quite close to Earth — perhaps dangerously close.

They’re known as Near-Earth Asteroids. Astronomers have discovered about 28,000 of them. They’re split into groups based on their orbits. Some stay inside Earth’s orbit, while others say just outside.

But two groups follow orbits that cross Earth’s. They’re known as Apollo and Aten asteroids, for the first known members of each group. Several hundred of them are at least one kilometer in diameter — big enough to cause a global catastrophe if they hit us. The odds of a collision are small. But hundreds of the asteroids are listed as “potentially hazardous,” so we can’t rule out impacts.

Perhaps the best known of these asteroids is Apophis, one of the Atens. It’s about a thousand feet across, and it’ll pass less than 20,000 miles from Earth in 2029. Scientists originally feared it might hit us then or later in the century. They’ve since ruled out that chance.

Two other asteroids will pass close to Earth on Friday. One will miss us by almost two million miles. But the other will pass just half a million miles away. More about that tomorrow.
 

Script by Damond Benningfield

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