Gallery: The Smallest Alien Planets

Super-Earth Exoplanet GJ 1214b

This artist’s impression shows the super-Earth exoplanet GJ 1214b passing in front of its faint red parent star. The exoplanet, orbiting a small star only 40 light-years away from us, is about 2.7 times the radius of Earth and has a mass about six times that of the Earth. GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes.

Three Planets Found Around Kepler-18 Star

This graphic shows the orbits of the three known planets orbiting Kepler-18 as compared to Mercury's orbit around the Sun. The bottom graphic shows the relative sizes of the Kepler-18 and its known planets to the Sun and Earth. One of the planets, Kepler-18b, is about twice the size of Earth.

Diagram of super-dense alien planet 55 Cancri e transiting host star

A simulation of the silhouette of planet 55 Cancri e, which is about 2.08 times the radius of Earth but has eight times the mass, transiting its parent star, compared to the Earth and Jupiter transiting our sun, as seen from outside the solar system. The star 55 Cancri A is nearly a twin of the sun and located 40 light-years from Earth in the constellation Cancer (the Crab).

55 Cancri star system location in sky

This wide-angle photograph of the night sky shows the location of 55 Cancri, a star where astronomers have found five planets, including a hot, dense super-Earth.

Alien Planet Kepler 19b

The "invisible" world Kepler-19c, seen in the foreground of this artist's conception, was discovered solely through its gravitational influence on the companion world Kepler-19b (the dot crossing the star's face). Kepler-19b is slightly more than twice the diameter of Earth, and is probably a "mini-Neptune." The planets orbit a star about 650 light-years away from Earth in the constellation Lyra.

Artist's Conception of Kepler-22b

This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. The planet is about 2.38 times the radius of Earth and in a star system 600 light-years from Earth.

Kepler-22 Star System Diagram

This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission.

Kepler Planets Diagram

Comparative sizes of planets discovered by Kepler. Jupiter, Neptune and Earth are shown for comparison as well. "RE" in the diagram means size relative to Earth or RE = Radius of the planet in Earth radii.

Kepler Planets Temperatures and Sizes Chart

Chart showing temperatures and relative sizes of the Kepler planets that have been discovered.