Upsilon Andromedae

The first main sequence star around which an extrasolar planetary system has been found. The discovery was announced in 1999 by a team from the San Francisco State University Planet Search (SFSU) group and independently by astronomers from the Harvard-Smithsonian Center for Astrophysics and the High Altitude Observatory in Boulder, Colorado, who had been studying the star for more than four years at the Whipple Observatory.

Prior to this, only single extrasolar planets. had been confirmed around Sun-like stars, together with two planetary systems around pulsars. A planet, with about two-thirds the mass of Jupiter, was found around upsilon Andromedae by the SFSU group in mid-1996. This became the fourth known epistellar jovian, having an orbit that brings it seven times closer to its host star than Mercury is to the Sun. Three years later, two companions of larger mass were announced orbiting at about 0.8 and 2.5 astronomical units.1 As one of the SFSU researchers, Debra Fischer, pointed out, this important discovery "implies that planets can form more easily than we ever imagined, and that our Milky Way is teeming with planetary systems."

The greatest surprise is the presence in one system of so many giant worlds. Theorists had only just begun to adjust to the idea of Jupiter-size planets in very small or highly elongated orbits. But this new triple-jovian system promises to cause an even bigger shake-up of ideas of planet formation. As to whether there might be life around upsilon Andromedae, that is impossible to say. The star's age is about 3 billion years-old enough for life to have evolved; however, further study will be needed to establish whether any Earth-like worlds are present.

Location Constellation: Andromeda Right Ascension: 01 36 48.527 Declination: 41 24 38.71 Distance from Sol: 52 Light Years Basic Data Alternate Designations: uAnd HR 458 HD 9826 Spectral Type: F8 V Apparent Magnitude: 4.09 B-V Color: 0.54 Mass: 1.34 Solar Masses Radius: 1.66 Solar Radii Effective Temperature: 6200 Kelvin Age: 5000 Million Years Habitability Inner Edge of Habitability Zone: 0.95 AU Outer Edge of Habitability Zone: 2.98 AU

Upsilon Andromedae b

Upsilon Andromedae b Statistics

Upsilon Andromedae C

Upsilon Andromedae C Statistics

The middle world of this system is cooler than the seething inner planet. It does not glow red from the heat of the star, but it is still too warm to maintain global cloud cover. This gives the world a Neptune-like appearance, albeit for completely different reasons. Whereas Neptune appears blue from the high levels of methane in the frigid atmosphere, upsilon Andromedae c appears blue for the same reason the sky on Earth does, Rayleigh scattering.

Upsilon Andromedae D

Upsilon Andromedae D Statistics

Weighing in at 4 Jupiter masses is upsilon Andromedae d, the outermost known planet in this new solar system. At an average distance of 2.5 AUs, this world is has a larger orbit than Mars. The planet would likely have total cloud cover and look quite similar to Jupiter. It's moons could be quite massive and would be mostly rocky worlds with large amounts of ice. Some of these moons may have vast tracks of their icy surfaces melted and featureless. Recent studies indicate that stars with epistellar planets, like upsilon Andromedae b, might emit superflares every century or so. If this is happening within the upsilon Andromedae system, then great areas of the icy moons of the outermost planet may have been melted smooth by these titanic stellar eruptions.

Planetary Orbits Around Upsilon Andromedae