The International Astronomical Union defines a planet as a celestial body that orbits the sun, is massive enough that gravity has forced it into a spherical shape, and has cleared away other objects ...

In the cold, dark outskirts of planetary systems far beyond the reach of the known planets, mysterious gas giants and planetary masses silently orbit their stars—sometimes thousands of astronomical ...

When you see art of our solar system as the planet orbit the sun, you may notice that Earth's orbit has a tilt. It is not a perfect circle. What's more, Earth is not the only planet that displays such ...

Astronomers have discovered more than 300 exoplanetary systems that have three or more known planets. Most of these planets are about the same size and spaced close together, earning them the moniker ...

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Kepler-11 is a sun-like star around which six planets orbit. At times, two or more planets pass in front of the star at once, as shown in this artist’s conception of a simultaneous transit of three ...

Planets are bodies that orbit a star and have sufficient gravitational mass that they form themselves into roughly spherical shapes that, in turn, exert gravitational force on smaller objects around ...

A possible cousin of Pluto seems to be circling the far reaches of the solar system. The dwarf planet candidate 2017 OF201 travels in a superwide orbit, with the sun relatively near one end of its ...

In what could be one of the strangest sightings, astronomers have discovered a planet in deep space with an unexpected orbit. What's more? It's orbiting two celestial objects that are neither suns, ...

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. Astronomers have ...