Gliese 581 e

Gliese 581 e /ˈɡliːzə/ or Gl 581 e is an extrasolar planet found around Gliese 581, a red dwarf star approximately 20.4 light-years away from Earth in the constellation of Libra. It is the third planet discovered in the system (fourth if the refuted planet candidate Gliese 581 d is included) and the first in order from the star.

The planet was discovered by an Observatory of Geneva team led by Michel Mayor, using the HARPS instrument on the European Southern Observatory 3.6 m (140 in) telescope in La Silla, Chile. The discovery was announced on 21 April 2009. Mayor's team employed the radial velocity technique, in which the orbit size and mass of a planet are determined based on the small perturbations it induces in its parent star's orbit via gravity.

At a minimum mass of 1.7 Earth masses, it is one of the least massive extrasolar planets discovered around a normal star, and relatively close in mass to Earth. At an orbital distance of just 0.03 AU (4,500,000 km) from its parent star, however, it orbits further in than the habitable zone. It is unlikely to possess an atmosphere due to its high temperature and strong radiation from the star. Although scientists think it probably has a rocky surface similar to Earth, it is also likely to experience intense tidal heating similar to (and likely more intense than) that affecting Jupiter's moon Io. Gliese 581 e completes an orbit of its sun in approximately 3.15 days.