36. Earth may have actually had two moons at one point. And no, we're not talking about 3753 Cruithne and Asteroid 2002 AA29. According to Space.com, it's possible (but not proven) that Earth ...

Advertisement Article continues below this ad Because Mars and Earth share so many ... to get an idea of what Mars may have been like in the past. If ancient Mars had liquid water, it would ...

Because Mars and Earth share ... surface once had liquid water. And these instruments have spotted minerals on its surface that scientists can analyze to get an idea of what Mars may have been ...