The early days of our solar system were a time of violence. Chunks of rock as big as mountains, moons, and even planets rammed into Earth and the other newly forming planets. A collision between Earth and a body as big as Mars probably led to the formation of the Moon. And another big collision may have flipped Venus upside down.
Mars took a pounding, too, and it has the scars to prove it -- including one that stretches half way around the planet.
Mars's northern and southern hemispheres are quite different. The north is low and fairly smooth, while the south is higher and rougher. And scientists think they finally know why: much of the northern hemisphere is covered by the largest impact crater in the solar system.
The scientists pieced together thousands of pictures from spacecraft in orbit around Mars. They also used measurements of the planet's gravity, and the height of its terrain.
The clues suggest that Mars got whacked by another large body almost four billion years ago, when the planet was young. The other body was probably at least 1200 miles in diameter. It hit Mars with a force equal to more than a million billion A-bombs like the one that destroyed Hiroshima.
The impact blasted out a crater that's more than 5,000 miles across, so it wraps about halfway around the planet's northern hemisphere -- a reminder of the violent early history of the solar system.
We'll have more about Mars tomorrow.
Script by Damond Benningfield, Copyright 2009
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