Most Martian meteorites found on Earth are believed to have been blasted into space during an event 175 million years ago, when a nuclear-strength meteoroid or asteroid impact on Mars caused the struck rock to reach escape velocity and leave the Martian orbit. From there, these meteorites followed elliptical orbits around the sun, with some intersecting the Earth’s orbit. Fewer were captured by the Earth’s gravitational field, and only 50 are known to have found their way to the Earth’s surface. Only two are chassignites. The subject of intense scientific study, chassignites are composed of iron-rich olivine and thought to have been formed deep in the Martian crust 1.36 billion years ago, when Mars was volcanically active.