Astronomers are closing in on one of the most tantalizing possibilities in planetary science, evidence that a previously unknown world may be lurking in the outer reaches of the solar system. The ...

A long-lost planet that helped create the Moon may have formed much closer to the Sun than scientists once thought, according to new research. Scientists have discovered that Theia, the ancient planet ...

We’ve found lots of “habitable” worlds but we don’t know what factors are needed for life. There are lots of reasons to search for planets around other stars—exoplanets. A big one is to find other ...