The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

Planet demographics reveal a puzzling lack of worlds in a certain size range throughout the galaxy F or centuries our solar system was the only planetary system known to humans. We had no proof other ...

Feb. 18 marks the 95th anniversary of the discovery of our outermost planet-not-planet. Here's what to know about the short ...

More than 1 million "interstellar objects" the size of the Statue of Liberty could be drifting unseen in the outer solar ...

A planet-size object that possibly once visited the solar system may have permanently changed our cosmic neighborhood by warping the orbits of the four outer planets, a new study suggests.

Scientists believe that two asteroids might be fragments of long-lost "planetary embryos" from the early solar system.

The solar system's biggest gas giant planet orbits an average of 484 million miles from the sun. The fourth planet from the sun, Mars, looks like a star but has a slightly ruddy hue. Mercury will ...

New research shows that star activity can distort exoplanet measurements, affecting size, temperature, and atmosphere ...