Meet the asteroids

Are they gonna hurt us?

Will they obliterate the earth?

How are asteroids found?

Did asteroids deliver life?

What are they made of?

What about comets?

Asteroids in orbit

Coming soon -- the ultimate extinction machines?
4 NOV 1998 Credit the blasted-from-space movies Deep Impact and Armageddon. Or blame the one-day scare from March, 1998, when headlines warned that a beefy asteroid could zoom within 30,000 kilometers of Earth -- or even sledgehammer our tender green planet -- in 2028.

spaceshipWithin a day, egg-bespattered astronomers used 1990 data to issue a revised estimate. It's safe to say that the asteroid will miss us by a good 600,000 kilometers -- about twice the distance of the moon.

From the movie "Armageddon". ©1998, Touchstone Pictures.

Still, the confluence of events has put The Why Files in an asteroidal frame of mind. Nobody knows the destruction that would result from a collision with one of these sub-planetary objects, but the evidence points to sudden, catastrophic and global damage. You could say it's pretty amazing that 1998 turned out to be a boom year for asteroids. Unlike planets, these misshapen agglomerations of rock and debris are not named for ancient gods. Instead they must answer to clunky handles like "1997 YF11" or "1998 ML14").

Asteroids are also far punier than planets: Ceres, the largest, is about 1,000 kilometers in diameter, but most are under a kilometer across. Most asteroids orbit between Mars and Jupiter, crashing into each other in a silent version of 3-D bumper cars that slowly grinds them to bits.

Puny but potent
Occasionally, an asteroid's orbit becomes more egg-shaped. As the orbit grows more elliptical, it eventually may begin crossing Earth's orbit and become subject to a collision with Earth.


Here's the orbit of the "killer" asteroid 1997 XF11. Once predicted to pass perilously close to Earth in 2028, current estimates give us at least 600,000 kilometers leeway.
Courtesy of the Minor Planet Center, Harvard-Smithsonian Center for Astrophysics.

1997XF11Small bits -- ranging up to maybe pebble size, may become the meteors that brighten our night sky. It's the rarer hunks that are more than 1 kilometer across that spawn doomsday scenarios and Hollywood thrillers.

The glare of attention on asteroids has also helped spark a flood of research on the link between asteroids and meteors, on why they leave the asteroid belt, and whether certain asteroids are masquerading as comets.

It's a sure sign of Halloween. So let's squelch the preamble and check out the rocks from the dawn of time. We satisfied our obsession with asteroids with information gathered at the October, 1998, meeting of the American Astronomical Society's Division for Planetary Sciences, conveniently held in Why-Files-ville -- Madison, Wis.

How bad can an asteroid impact get?

The Why Files
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The Why Files Staff includes: Terry Devitt, editor; Darrell Schulte, webmaster; David Tenenbaum, feature writer; Susan Trebach, spiritual advisor