are chunks of rock orbiting the Sun. This one is Ida, and it is
about 30 miles long. Most of the asteroids, like Ida, move in circular
orbits between the planets Mars and Jupiter. These asteroids will
never collide with Earth. However, a few asteroids move in elliptical
orbits which cross the orbits of the other planets, including the
Earth. Below are four radar images of one of those "Earth-crossing"
asteroids. Above: Galileo image of
Ioa. Image courtesy of Jet Propulsion Laboratory. Below: Asteroid
Toutatis. Image courtesy of NSSDC.
This is the
double asteroid Toutatis. Like all of the known asteroids whose
orbits cross the Earth's, the two pieces of Toutatis are quite small
--only a few miles across. But more Earth-crossing asteroids
are found every year, and being hit by even a "small"
asteroid "only" a mile across would be a major disaster!
(The asteroid that made Meteor Crater was only about 50 feet across!)
In the case of Toutatis, the impact would produce a double crater
like other double or chain craters
already found on the Earth.