The journey to the Earth
How did these rocks from Mars end up on Earth? Only one thing could send a piece of rock flying out fast enough to escape Mars's gravity: an asteroid or comet slamming into Mars. Mars's gravity is about one-third as strong as Earth's, and its atmosphere is about 125 times thinner, so it is easier to eject a rock from Mars than from Earth. After orbiting the Sun for more than a million years, some of the ejected pieces eventually struck Earth as meteorites.
Found October 30 1999, Los Angeles County, California, USA
Keywords: Asteroids, Astrogeology, Astrophysics, Mars (Planet)--Atmosphere, Meteorites