NASA » Near Earth Asteroids What are they and where do they come
from? By David K. Lynch, Copyright © 2007 All Rights Reserved.
Ever since the Earth formed 4.5 billion years ago, it has been
bombarded with rocks from space. Each year about 50,000 tons of
asteroidal material enters the Earth’s atmosphere. Most of it
burns up high in the ionosphere due to friction with air. But a
few rocks get through. Impacts in the ocean pass unnoticed,
though the larger ones could produce tsunamis. Others strike
land and leave craters. This has been going on since the dawn of
time and is expected to continue long after the Sun boils away
our oceans in about 5 Artist's conception of a asteroid impact.
NASA image. Large space rocks are called asteroids, and small
ones are called meteoroids. When they streak through the
atmosphere they are termed meteors , or “shooting stars”. If
they reach the ground, they are called meteorites. Where Do They
Come From? The origin of comets and asteroids is not completely
understood. Some aste