Martian meteorites - visitors from a nearby planet.
There is a group of meteorites whose characteristics suggest that they did not originate on an asteroid and are between 1.3 billion and 150 million years old. This means that they came from a geologically active planet-sized body that has been hot or even molten for a long time.
But what planet? There is some evidence that these rocks come from Mars.
The evidence that allowed scientists to deduce their origin is as follows - First, the texture of the vast majority of the rocks is igneous. This means that they were formed from molten rock. Second, although these rocks contain the same minerals found in asteroidal meteorites, there are differences in the proportions of some elements. Thirdly, their age suggests that they came from a planet-sized body. And fourth, meteorites from Mars have the same ratio of gases trapped inside as the Martian atmosphere.
Rocks are released into space from Mars by the impact of another body on the planet's surface. The body must have tremendous velocity and strike the surface of Mars at such an angle that the ejected rocks can overcome the gravity of Mars and penetrate the orbit of the Sun. Since there is very little chance that the ejected rocks will land on our planet Earth, meteorites from Mars are very rare and valuable.
One very famous meteorite that also originated on Mars is Allan Hills 84001, which we have also written about in the past. Its age of 4.1 billion years sets it apart from the others.