Mars is about 140 million miles from our cozy planet. A human mission to that cold, rocky neighbor would mean being away from Earth for about 3 years. But the things those explorers would see and ...

A mysterious interstellar comet — just the third such object ever confirmed to have entered our solar system — streaked past Mars last week. Subscribe to read this story ad-free Get unlimited access ...

Mercury, Venus, and Mars sit within the same general neighborhood as Earth, yet each has followed a radically different path. One kept a magnetic field against the odds. Another trapped so much heat ...