"These objects really could be anywhere in the solar system at any given time." One million alien visitors from another star system could already be lurking in the solar system. We aren't talking ...

Everyone knows about the Solar System, and the planets that make it up. They’re in space, orbiting the Sun, in an order we all at least used to be able to recite. But it was not always so.

With a radius of 3,959 miles, Earth is the fifth largest planet in our solar system, and it's the only one known for sure to have liquid water on its surface. Earth is also unique in terms of ...