To be a planet, NASA says an object must be big enough that its gravity has cleared away any other objects of a similar size near its orbit around the Sun. I can understand how something can clear ...

Astronomers have long been puzzled by a cosmic mystery: planets orbiting two stars—like Star Wars’ Tatooine—are surprisingly rare, even though they should be common. New research suggests the culprit ...

This is a brilliant question because the notion of an orbit is counterintuitive. We know that massive objects (really, any objects with mass) gravitationally attract other massive objects; Newton's ...

Thanks to the discovery of thousands of exoplanets to date, we know that planets bigger than Earth but smaller than Neptune orbit most stars. Oddly, our sun lacks such a planet. That's been a source ...

A nearby star system with two suns could potentially support an Earth-sized planet in a region where liquid water could exist ...