Add Yahoo as a preferred source to see more of our stories on Google. A planet-forming disk made from rock and gas surrounds a young star. NASA/JPL-Caltech/SwRI/MSSS ...

Something strange may be lurking in the outer solar system. The odd orbits of distant space rocks suggest there’s a giant, elusive world dubbed Planet Nine waiting out there to be discovered. But now, ...

Some of the most distant rocks in our solar system act in a way that suggests there’s some massive object out there we haven’t been able to see. A planet? Maybe. But why not a small black hole? That’s ...

There’s something about comparing the sizes of unthinkably large objects that’s endlessly intriguing. Looking at a comparison of all the various sizes of stars in the universe, for example, makes for ...