It’s a Bird, It’s a Plane, It’s … a Rock

by Bill Chameides | October 11th, 2010
posted by Erica Rowell (Editor)

Permalink | 1 comment

Two images of 2010 ST3 (circled in green) taken by PS1 on the night of September 16 show the asteroid moving against the background field of stars and galaxies. (Credit: PS1SC)

This post has been updated.

News flash: An asteroid is headed our way.

Here’s a little quiz for a Monday: What’s close by and at the same time more than a million miles away? Answer: 2010 ST3.

Next question: Huh?

OK. You remember the debate about what caused the Younger Dryas, that major cold snap some 12,000 years ago? And that one theory was it was caused by an extraterrestrial impact?

We don’t know whether such an event actually caused the Younger Dryas, but we do know that impacts from large space objects like asteroids and comets occur and can cause havoc here on Earth. (See here, here and here.)

And so, even though the chances of such an event actually occurring in our lifetimes are quite slim, NASA keeps a lookout for them. The idea being that if we detect an object on a collision course with our planet early enough, we could do something about it — maybe launch a space mission to deflect it or send a nuclear warhead into space to blast it to smithereens. The problem is that getting such a project off the ground might require a resolution by the United Nations or an act of Congress, in which case, by the time everyone agreed, the rock would have already devastated us. But not to worry — that’s why we have Superman. (I’m just concerned he won’t be able to find a phone booth, they’re in such short supply these days.)

Setting Sights on Smaller Near-Earth Objects Pays Off

Anyway, NASA already has a pretty good catalog of the large objects that are out there in our patch of the universe, but not so much the smaller ones — those that are less than a mile in diameter. These smaller space objects hit the Earth every few thousand years. While they generally break up in the atmosphere before reaching terra firma, the resulting fireball can cause regional-scale devastation. With the launch of the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) PS1 telescope this past summer, we’ve gotten a whole lot better at detecting these smaller near-Earth objects

The Pan-STARRS has already hit paydirt — well, space rock. Its first find is named 2010 ST3. The rock, roughly 150 feet (or about half a football field) in diameter, was first detected when it was 20 million miles away — how’s that for eagle eyes? But it’s rapidly closing and will pass within a mere four million miles of the Earth in mid-October. Given its near-Earth trajectory, 2010 ST3 is now categorized as a potentially hazardous object (PHO). Not a threat on this pass, but it could possibly collide with the Earth in 2098.

How Close Is Close, in Astronomical Terms

One measure of how close an object will pass to the Earth is the average distance between it and the moon or roughly 239,000 miles — this is known as a lunar distance (LD). 2010 ST3 will pass within 17 LDs of the Earth. There are plenty of PHOs that will pass much closer to us — of the roughly 80 or so that will do so between now and the end of the year, two will come within five LDs of our planet. Now, that’s over a million miles away, plenty of room for error, but in astronomical terms, it’s quite close.

So the next time your attention wanders mid-conversation and the person you’re speaking with complains that you’re “a million miles away,” just tell him, “I’ve got PHOs on my mind.” Then run out of the room and head for the nearest phone booth. Just keep in mind that you may have to travel a million miles to find one.

This post has been revised to reflect the following correction:
Correction: October 11, 2010 6:43 pm
As initially published, the post referred to the approximate size of the asteroid’s diameter as about a football and a half; in fact, the approximate size is half a football field.

Further Reading

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1 Comment

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  1. Blake Rodgers
    Oct 11, 2010

    150 ft. would be half a football field, not 1.5.

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