Super-Earth, also known as superterran planet or themian planet, is a classification of planet with mass ranging from 2 to 10 Earth masses or 0.0063 to 0.0315 Jupiter masses. Hence it is the fifth most massive mass class of planet, super-Earth is rated M-Class V and has the symbol Ea.
Some super-Earths have rocky surface like Earth, and some are gaseous or icy like Uranus and Neptune. Deep ocean planets (with oceans hundreds or thousands of miles deep) would also be a common property of super-Earths.
Super-Earths tend to be more geologically active than Earth's, making such worlds more volcanically active but prohibiting plate tectonics due to stronger convection currents in their mantles owing to their stronger gravity, making the surfaces too strong for magma to break into plates. Also because those planets tend to have gravity two or three times stronger than Earth's prohibiting plate tectonics, mountains would be rare on super-Earths with elevations no more than a mile high.
Habitability and life Edit
The habitability of super-Earths depend on if it's rocky or gaseous. If it's rocky, it would typically have very thick atmosphere, perhaps ten times thicker than it is on Earth for super-Earths in the habitable zone. Because of the stronger gravitational pull of super-Earths (perhaps two to three times stronger than Earth's) than lower mass planets, creatures would not grow and develop as effeciently as those on Earth. But because of their thicker atmospheres, there may be floating lifeforms, such as "balloon gondolas."
If it is an ocean planet, every lifeforms are aquatic with no aerial lifeforms unless if organisms can both swim and fly, so-called "aquaerial life." There might even be phytoplankton covering large areas of the ocean, perhaps as large as continents on Earth. So fish would be a dominant form of life on ocean planets but no birds, unless if there is a creature called birdfish, an aquaerial organism.
There are an estimated 155 billion super-Earths in our galaxy alone, making it the third most abundant mass class of planet after mid-Earth and sub-Earth. This corresponds that 189‰ of all 820 billion planets in our galaxy are super-Earths.
Known super-Earths Edit
There are no super-Earths in our solar system, but there are more than 400 such planets known around other stars as of 2015. The first super-Earth discovered was Ixion PSR B1257+12 c (Ixion) on January 22, 1992, together with the other super-Earth in that planetary system orbiting around the pulsar. The first super-Earth around the normal star would not be discovered until 2004, when 55 Cancri e (Euippe) was found. The second super-Earth found was Gliese 876 d (Ilus). The first super-Earth in the habitable zone was Gliese 581 d (Themis). Other examples of super-Earths are COROT-7b (Icarus), GJ 1214 b (Shesha), and Tau Ceti f (Poseidon), one of five known super-Earths around Tau Ceti. Kepler space observatory has found hundreds of super-Earths, including the habitable planets Kepler-22b (Gayatri), Kepler-62f (Likho), Kepler-186f, Kepler-438b, and Kepler-442b. Gliese 667 Cc (Cresphontes) is the most Earth-like planet known that was not observed by Kepler.