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

Disaster flick
craterMost asteroids (and the orbiting snowballs called comets) tend to mind their own business, appearing mainly as smudges against the starry background in telescopic images.

Three-dimensionalmap of local gravity and magnetic field variations of Chicxulub crater in the Yucatan penninsula. The impact basin is buried under sediment, hiding it from view. Courtesy Natural Resources Canada.

But comets and asteroids can be real players in Earthly events. The reason is simply that they carry so much energy due to their enormous speeds. Kinetic energy equals one-half of mass times velocity squared, and asteroids and comets typically impact at between 11.2 and 70 kilometers per second. (That's between 25,000 and 156,250 miles per hour.) In other words, a big impact could carry the energy contained in all the nuclear weapons ever made -- or more.

Many astronomers and biologists think a big comet or asteroid caused the dinosaurs to go extinct 65 million years ago, when a 10- to 15-kilometer wide uncontrolled flying object whacked the Caribbean Sea, forming a crater about 180 kilometers in diameter near the Yucatan Peninsula (see "The End of Evolution " in the bibliography).

The heat of impact with the atmosphere and surface caused a firestorm over much of North America. Then vast clouds of dust and smoke shaded the planet, causing a cold spell that terminated the million-century plus reign of Barney and his fellow dinos.

The annihilation of the dinosaurs, in turn, allowed the more adaptable mammals to gain center stage, leading immediately to cultural triumphs like the Flintstones, and Beverly Hills 90210. Want more details on the collision?
Hangin with Elvis
If you doubt this asteroidal destruction theory, glare at the moon. Although it never had dinos, the moon has obviously been pummeled over the eons by a rain of interplanetary junk. And according to current theories, the moon itself was formed when Earth was hit up-side the head by a flying piece of debris about, say, the size of Mars, give or take a couple of kilograms. (See "Lunar Prospector Probes..." in the bibliography).

Nevertheless, the life of the asteroid is no picnic. In the asteroid belt, they continually bash each other, and it's the rare asteroid nowadays that's larger than 1 kilometer in diameter. And while asteroids may threaten Earth if they depart the asteroid belt, those that do are eventually lured by the sun's gravitation into fiery oblivion.

What are your odds of being wasted by an asteroid?

back more
The Why Files
There are 1 2 3 4 5 6 7 8 pages in this feature.
Bibliography | Credits | Feedback | Search

©1998, University of Wisconsin, Board of Regents.