In astronomy, double planet and binary planet are informal terms used to describe a binary system

Binary system (astronomy)

A binary system is an astronomical term referring to two objects in space which are so close that their gravitational interaction causes them to orbit about a common center of mass. Some definitions A binary system is an astronomical term referring to two objects in space (usually stars, but also...

 of two astronomical object

Astronomical object

Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...

s that each satisfy the definition of planet

Definition of planet

The definition of planet, since the word was coined by the ancient Greeks, has included within its scope a wide range of celestial bodies. Greek astronomers employed the term asteres planetai , "wandering stars", for objects which apparently move over the sky...

 and that are near enough to each other to have a significant gravitational effect on each other compared with the effect of the star(s) they orbit. As of 2010, there are no officially classified double planets in our Solar system.

Similarly, there are also binary asteroid

Binary asteroid

A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...

s (also known as double minor planets) such as 90 Antiope

90 Antiope

The most remarkable feature of Antiope is that it consists of two components of almost equal size , making it a truly "double" asteroid. Its binary nature was discovered on 10 August 2000 by a group of astronomers using adaptive optics at the Keck Telescope on Mauna Kea. The "secondary" is...

, and binary Kuiper belt objects (KBOs) such as (79360) 1997 CS29

(79360) 1997 CS29

, also written as 1997 CS29, is a double cubewano. It was discovered on February 3, 1997 by Jane X. Luu, David C. Jewitt, Chad Trujillo, and Jun Chen at the Mauna Kea Observatory, Hawaii.-Orbit:...

 and 1998 WW31

1998 WW31

' is a double Kuiper belt object. It was discovered in 1998 by the Deep Ecliptic Survey . forms a binary system with another object with the IAU provisional designation : the first trans-Neptunian binary to be discovered since Pluto, and one of the most symmetrical binaries known in the Solar System...

.