National Geographic : 2014 Apr
Earth Venus Mercury Asteroid belt Mars Jupiter Pallas THE ASTEROID BELT THE MOON AND MARS Hygiea Ceres Vesta About 50 percent of the belt’s mass is in these four asteroids: Asteroid impacts expel debris, called ejecta. are from the asteroid belt 99.8% 99.8% are from Vesta alone 6% 6% are ejecta from the moon and Mars 0.2% Where meteorites originate Falling objects Meteorites on Earth NEXT On Deflection Asteroids of the size that caused the meteor explosion over Russia in 2013 may plunge into the atmosphere every 30 years—ten times more often than once thought. Veteran astronaut Tom Jones says that early warning could stop them. Robotic missions could ram an asteroid or hover to exert a gravitational tug. This might shift an asteroid’s velocity enough, he says, “to make it miss its appointment with Earth.” — Eve Conant GRAphic: pERiscopic. souRcEs: JEffREy N. GRossmAN ANd michAEl E. ZolENsky, NAsA METEOR These trails of light created by vaporizing particles are also called shooting stars. METEOROID smaller than asteroids, these tiny chunks of debris orbit the sun, and some fall to Earth. METEORITIC DUST up to 100 tons of fragments and particles, including remnants from the solar system’s formation, enter Earth’s atmosphere daily. The largest surviving meteorite on Earth is in Namibia. it weighs about 60 tons. The meteor that exploded over chelyabinsk, Russia, is the largest known object to enter Earth’s atmosphere since 1908. of its 13,200 tons, 76 percent vaporized above Earth. METEORITE A meteorite is the part of an asteroid or comet that reaches Earth’s surface. The average meteorite weighs about an ounce, equivalent to a large marble.