I'm bringing out my nerdy side today..I've pieced a few articles together to compile some really interesting information about some recent discoveries about the Gliese 581 system. :)
--LS

Scientists Find Life on Another Planet?

Not exactly, but it may be the closest we’ve come yet. A team of planet hunters from the University of California (UC) Santa Cruz, and the Carnegie Institution of Washington has recently discovered the first potentially habitable exoplanet. Although this news is extremely exciting, a potentially habitable planet only means a planet that has the possibility to sustain life but does not have to mean one where human life could succeed.

The newly discovered planet Gliese 581g is located within the Gliese 581 system in the Libra constellation. The system is named after the host star Gliese 581 which is a red dwarf star located 20.5 light-years from Earth. Gliese 581 is much like other red dwarf stars so it is much dimmer in contrast to our own sun as well as about only 30 percent of the mass of our sun. The star is believed to be approximately a few billion years old and apparently relatively stable which makes theories of evolution of life a possibility.

The planet Gliese 581g is one of 6 planets which, much like our solar system, orbit Gliese 581in a near-circular orbit. This particular planet Gliese 581g is located directly within the habitable zone, which is the distance from a star where an Earth-like planet can maintain liquid water on its surface and Earth-like life. The habitable zone is the intersection of two regions, a planetary system and a galaxy which are both favorable to life.

Gliese 581 System Compared to Our Solar System

There are two other planets in the Gliese 581 system located on the edges on the habitable zone. Gliese 581c is located on the hot side of the system. Its mass is 5.36 times that of the Earth which classifies it as a super-Earth. The planet is 0.073 AU from Gliese 581, making its orbital rotation every 15 days. It was once thought to be the first Earth-like planet within the habitable zone, but upon further research it was suggested the planet would be too hot to contain liquid water or life.

Gliese 581d is 7-8 times the Earth’s mass, putting it in the same category as Gliese 581c, a super-Earth. It resides on the cold edge of the habitable zone and since it is 0.22 AU from its parent star, it completes its orbit every 67 days. There is a possibility it may be habitable with a thick atmosphere and a strong warming greenhouse gas effect.

The other planets in the Gliese 581 system are far outside the habitable zone. Gliese 581e and Gliese 581b are much too hot to sustain life as they are very close to their parents star. Planet e is 0.033 AU from its parent star and orbits every 3.15 days while planet b is 0.014 AU from Gliese 581 and completes its orbit every 5.4 days.

Gliese 581f is the sixth and farthest planet in the Gliese 581 system being 0.76 AU from its parent star. This planet is much too cold and cannot sustain life. Although it is the farthest planet, it is still closer to its parent star than we are to the sun.

Artists Depection of Gliese 581g and its Solar System

Gliese 581g is the only planet located in the habitable zone. It is only 0.146 AU from Gliese 151 giving it an orbit of 37 days. Although it is close to its parent star, it is 20 light years away from our Earth. It is an Earth-size planet being only 3-4 times the size of our Earth with a diameter 1.2-1.4 times the Earth’s. The mass of this planet gives way to suggestion of a rocky planet containing a definite surface and a similar gravitational force as ours. The planet is tidally locked, meaning one side is always facing the star which gives that side perpetual daylight while the other side receives perpetual darkness. The optimal spot for humans would be in the “grey” zone, a band located along the planets perimeter between shadow and light. This line is also called the “terminator.” Gliese 581g’s average surface temperature is thought to be between -31˚C and -12˚C.

GLIESE 581g FACT FILE

Diameter - 1.2 to 1.4 times that of the Earth
Mass - 3.1 and 4.3 times that of the Earth
Average surface temperature - between -24˚F and 10˚F (-31˚C and -12˚C)
Distance from the Earth - 20 light years or 118,000,000,000,000 miles
Time needed to travel to Gliese 581g in a rocket travelling one tenth the speed of light, or 19,000 miles per second - 200 years
One of six planets to orbit the star Gliese 581
Length of year - 37 Earth days
Gravity - similar or slightly higher than Earth
Distance from its sun - around six million miles
The planet orbits a red dwarf which is 50 times cooler and a third the size of our Sun
Composition - rocky with liquid water and atmosphere.
One astronomical unit, or AU, is the average distance between the Earth and sun, about 93 million miles (150 million km)