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

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

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 ...

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.

This may explain the strange properties of the orbits of our solar system's planets, which are not quite perfectly circular, and all lie on slightly different planes. NASA artist’s conception of ...

And being so close to the sun, it will be difficult to see. With eight planets in our solar system, they all have some very interesting traits. Here's a quick look at the planets aligning on this ...

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

Temperamental' stars that brighten and dim over a matter of hours or days may be distorting our view of thousands of distant ...

All of our solar system’s planets are lining up to parade through the night sky at once. This extraordinary celestial event will see the sky scattered with seven visible planets in what is known ...