The Other (Known?) Solar System

By Jim Ward

You probably saw this on the TV as this is old news. Astronomers (professional ones, that is) announced in April that they have found evidence of a multi-planet Solar System other than our own. Previously, they had found stars that apparently had a single giant planet orbiting them. Now, scientists at San Francisco State University say that they have found a system with three huge planets.

The system is associated with the star Upsilon Andromedae, which is 43.9 light years away from us, which makes it relatively close-by.

u Andromedae is a star of the spectral type F8V, is light yellow in colour, and has an apparent magnitude of +4.1 with an absolute magnitude of +3.45. It is therefore slightly more luminous than our own Sun and also slightly hotter, which is of spectral type G2V and is yellow in colour.

The innermost of the planets, first discovered in 1996, is about 75% of the mass of Jupiter, which is 318 times the size of Earth. It orbits very close to its Star and its year is 4.6 Earth-days.

The middle planet has the mass of 2 Jupiters, and orbits its Star at a distance of approximately 110 million kilometres, taking 242 Earth-days.

The outermost planet is four times Jupiter's mass, and orbits u And at approximately 300 - 450 million kilometres, taking 3' to 4 years.

All three planets have pronounced elliptical orbits, as opposed to nearly circular ones as are found in our solar system (with the exception of Pluto's).

The search for extra-solar planets began in an organised way in 1987, and the first one was found in 1995. To date, there are known to be at least 20 extra-solar planets, all of them giants.

The planets were not found optically, but were detected by monitoring the host star's characteristic wobble in space, resulting from the gravitational tugs of the giant plants. A planet the size of Earth could not be found by this method since Earth's gravitational pull is microscopic by comparison, and would not cause the star to wobble discernibly.