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The Planets of Andromeda

When astronomers talk about Andromeda, they could be referring to two different entities in space. The first is a galaxy, found more than 2.5 light years away from the Milky Way, formally called Messier 31 but commonly known as the Andromeda Galaxy. It is the closest spiral galaxy and surges closer to Earth each year. Under normal circumstances, it would be impossible to see any planets in this galaxy because of its distance from Earth, but in 2009 the gravitational field of a closer object acted as a magnifying glass to M31, allowing scientists to locate a single planet there. This phenomenon is called microlensing. The other entity is formally referred to as Upsilon Andromedae, a star located in the Milky Way galaxy. Three large gaseous planets have been discovered around this star. Both the galaxy and the star acquired their names by being located around the Andromeda constellation.

Messier 31 Planet
- In 2009, scientists went public with the discovery of a singular planet in the outer reaches of M31. When they first observed the planet in 2004, during the microlensing event, they assumed they were seeing two stars orbiting each other. Through extensive study and simulations, they later came to the conclusion that what they had actually seen was a gaseous planet, roughly six times the size of Jupiter, orbiting around a greater star.
Upsilon Andromedae Planet 1
- Astronomers found the first planet circling Upsilon Andromedae in 1996. It is the innermost of the three planets and contains at least three-fourths the mass of Jupiter. It is located very close to the star and orbits once every 4.6 days. That's only 15 percent of Mercury's distance to Earth's sun. Scientists are puzzled as to how and why such a large planet can circle its star so closely.
Upsilon Andromedae Planet 2
- Scientists discovered the middle planet orbiting Upsilon Andromedae after years of research into why the star seemed to have excess forces tugging upon it. It is twice the mass of Jupiter and circles its star just a bit more closely than the Earth circles the sun. Its orbit takes 242 days to complete, making it similar in distance and path to Venus.
Upsilon Andromedae Planet 3
- Planet 3 of Upsilon Andromedae was discovered when the second planet did not explain the scattered motion pattern of the star. Astronomers studied the wobbly star and found through extensive simulations that three large, gaseous planets could co-exist in stable orbits around it. This outermost planet has a mass four times that of Jupiter and circles the star once every three and a half years. Its orbit is oval in shape. The three-star solar system could, with more study, completely revamp the scientific theories on how planets are formed.

Astronomy