Super-Earths are a type of extrasolar planet with a mass higher than Earth’s, but lower than that of a gas giant. The term super-Earth refers only to the mass of the planet; it does not imply anything about the surface conditions or habitability. There is no official definition for super-Earth, but the generally accepted range of masses is 1 to 10 times that of Earth (M⊕).
Super-Earths are thought to be common in our galaxy. In fact, recent estimates suggest that as many as one in six stars has a super-Earth orbiting it. The first confirmed super-Earth was discovered in 2005 orbiting Gliese 876, a red dwarf star just 15 light years away from Earth. This planet, named Gliese 876b, has a mass 4.5 times that of Earth and an orbital period just over 2 days.
Since their initial discovery, hundreds more super-Earths have been found by various methods including radial velocity and transit photometry. These planets are typically found orbiting close to their host stars (within 0.1 AU) and have short orbital periods (less than 100 days). Due to their small size and close proximity to their stars, these planets are often referred to as “hot Jupiters”. However, unlike Jupiter which is mostly composed of gas and has no solid surface, most super-Earths are thought to be rocky worlds with surfaces similar to our own world’s.
The high abundance of super-Earths suggests that they may be very common in our Milky Way galaxy – possibly even more common than singleton Earths like our own Solar System’s sole planetary inhabitant. If this is indeed the case then there could be billions of rocky worlds out there waiting to be discovered!