National Research Council of Canada. Herzberg Astronomy and Astrophysics
In 1996 scientists found a little piece of Mars on the Antarctic Ice Cap. A meteoric impact on Mars in the remote past had knocked bits of the Red Planet into space, and some of those fragments eventually found their way to Earth. They knew this one was from Mars because of the minerals in it and because it contained bubbles of Mars’ atmosphere. Some of the minerals required liquid water to form, and in the Solar System, every planet’s atmosphere is unique.