Astronomers are closing in on what looks like a rare prize: a world almost the size of Earth, circling a Sun-like star at a distance that gives it a familiar, year-long orbit. The candidate, known as ...

Astronomers believe they have uncovered evidence of a previously unknown ninth planet lurking in the not-too-distant reaches of the solar system. This hypothetical world, dubbed "Planet Y," could be ...

The object, the latest “quasi-moon” detected by astronomers, could be with us for almost another 60 years. By Robin George Andrews The Earth stands alone in the solar system as a habitable world, as ...

Exoplanets are planets that orbit stars other than the sun and thus exist outside the solar system. The word "exoplanet" ...