The planet is about 1.5 times larger than the Earth and has about five times more mass than the Earth. Also, it is the first exoplanet (or extrasolar planet: a planet outside of the solar system) to be discovered that orbits its star within what is considered a habitable zone for the existence of liquid water. The team thinks that the planet’s surface temperature is between 0 and 40 degrees Celsius (32 and 104 degrees Fahrenheit).
The star Gliese 581 is in the constellation Libra. It is one of one-hundred stars that are closest to the Earth. Its distance of 20.5 light-years (LYs) away makes it about 123 trillion miles (205 trillion kilometers) from the Earth. (One light-year is the distance that light travels in vacuum in one year—a distance of about 6 trillion miles, or 10 trillion kilometers.) In addition, the star is about one third the size of the Sun.
Also orbiting Gliese 581 is a larger planet, Gliese 581 b, which is about the size of the planet Neptune. It was discovered on November 30, 2005 by a team of Swiss and French astronomers. The planet Neptune, the eighth farthest planet from the Sun, is about 17 times more massive than the Earth.
Astronomers are also searching for a third planet about Gliese 581, which the European team think could be about eight times larger than the Earth.
Additional information is contained at Space.com: http://www.space.com/scienceastronomy/070424_hab_exoplanet.html.