Upsilon Andromedae e

Upsilon Andromedae e is the outermost extrasolar planet orbiting the star Upsilon Andromedae A in the constellation of Andromeda. This planet is one of the most Jupiter-like exoplanets found in terms of mass and semi-major axis.

Discovery
This planet was discovered on November 22, 2010, but the discovery paper was not released until December 2. It was the fourth time in 2010 that a fourth planet has been discovered in a planetary system, the others being Gliese 876 e, HD 10180 e, and HR 8799 e; in no other year so far during the exoplanet era has more than one fourth planet been discovered.

Astronomers originally thought that this planet could not exist because it would have made the planetary system unstable and would have been ejected. But in 2007, an island region of stability was reported where a fourth planet could exist.

Characteristics
Upsilon Andromedae e is a so-called “Jupiter-twin” because it has a mass slightly greater than Jupiter's and orbits at a similar distance as Jupiter from the Sun, at precisely 5.2456 AU compared to 5.2043 AU for Jupiter. Although only the minimum mass is determined since inclination is not yet known, its true mass might be much greater. It takes over a decade to orbit the star. At an eccentricity of 0.00536, the planet's orbit is more circular than that of any of the planets in our solar system.