A composite picture of (from left to right) Mars, Phobos, and Deimos. A giant impact could have formed these two small moons, according to a new paper. NASA

A Huge Asteroid Hitting Mars 4 Billion Years Ago May Have Shaped the Red Planet

A new study supports the idea that the sculpting of Mars and its two small moons was largely determined by a huge impact early in the solar system's history.