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The new planet orbits the cool and dim main sequence M-class (M2.5 V) red dwarf star Gliese 581, which lies about 20.4 light years (about 120 trillion miles) away from Earth, in the constellation Libra (the Scales). The newly discovered world is also 14 times closer to its parent star than the Earth is to the Sun, which gives it an orbital rotation rate of approximately 13 days (here on Earth).

Unlike all the other extra-solar planets found to date, Gliese 581 C lies within the habitable zone of its star, despite being so close. That's because the star is 50 times fainter than our own sun (and much cooler temperature-wise).

Two other planets are known to inhabit the system. One is a Neptune-sized gas giant about 15 times more massive than Earth which orbits even closer to the star than Gliese 581 C does. The other is an 8 Earth-mass planet discovered at the same time as Gliese 581 C, but lies outside of the star's habitable zone and may have an orbital period of 84 (Earth) days.

A Strange, New World

Gliese 581 C, estimated to be fifty percent larger than Earth and five times as massive, is believed to be a terrestrial world, with a rocky surface possibly covered by oceans. Stephane Udry, the study leader at the Geneva Observatory in Switzerland hypothesized that the mean average temperature of Gliese 581 C lies between 0 and 40 degrees Celsius (32 to 104 degrees Fahrenheit), temperatures that are ideal for liquid water. It is possible, however, that the world could have burned off whatever oceans may have been on the planet's surface when the star was hotter than it is now, theorizes planet hunter David Bennet of the University of Notre Dame in Indiana (who was not involved in the discovery of this new world), who had this to say about the discovery.

"These low-mass stars are the ones where we are going to be able to discover planets in the habitable zone first"

It is possible however, that the planet could be an icy ball, which means it would be even larger, suggests Michel Mayor, one of the eleven astronomers involved in the discovery of Gliese 581 C. He also stated that (based on current theories about the planet) Gliese 581 C should have an atmosphere, but is cautions that the composition of the atmosphere is still unknown at this time, and if it's too thick, the planet could be too hot to support liquid water - or even life as we know it.

David Spergel, chairman of the astrophysics department at Princeton University, however, has another theory. He states that if the planet is indeed a rocky, terrestrial world, it would be tidally locked to its parent star the same way our moon is to the Earth - which means that Gliese 581 C must always show the same side to the star. This would mean that one side of the planet is always too hot to support life, and that the other side would be too cold. He does concede however, that at the terminator - the margin between the hottest and coldest parts of the planet, liquid water could exist; however hurricane strength winds would be present. While Gliese 581 C would be a radically different planet to Earth, it is theoretically possible that life could exist in that hellish environment. As Spergel said, "this is a big, impressive step."

How It Was Found

Gliese 581 C was discovered using the HARP (High Accuracy Radial Velocity for Planetary Searcher) spectrograph attached to the European Southern Observatory's 3.6 meter telescope at La Silla, Chile using the radial velocity, or "wobble" technique, which determines the size and mass of a planet based on small perturbations induced in the parent star's orbit via gravity.

Study leader Stephane Udry of the Geneva Observatory in Switzerland said there was some time beteween the calculation of the planet's size and the realization that it was within the star's habitable zone. "That came at the end," Udry said. When he did realize it, he knew he'd be spending time fielding phone calls from the media. "You right away think about the journalists who will like it very much,” he told SPACE.com.

If You Were There

If you were to stand on the surface of Gliese 581 C (assuming you could, of course), you'd quickly notice that you're a lot heavier than you would be if you were still here on Earth. The gravity on this world is roughly 1.6 times as strong as Earth's, so if you weigh 150 pounds on Earth, your weight would increase to 240 pounds on Gliese 581 C.

Also, you wouldn't have to wait very long to start collecting your first Social Security checks either. A year on Gliese 581 C is only about 13 days (think two weeks). Put a change of address in with the US Government to Gliese 581 C, and not only would you not have to pay income taxes (as you would be decidedly "out of the country") but you also would have to wait only a couple of years (as opposed to your entire working life) before you'd be 67 years old (assuming you were transported from Earth to Gliese 581 C at the age of 16). The drawback? Well, assuming you were able to live there, you'd have practically nothing to draw from Social Security since you would have never been able to contribute anything to the system. Oh well, so much for that idea.

Looking up at the sky would also reveal an impressive sight. Udry believes that the red dwarf star would hang in the sky at a size roughly 20 times larger than our moon. As the old saying goes, don't look up (at least during the day).

Sources:
http://news.yahoo.com/s/ap/20070425/ap_on_sc/habitable_planet
http://news.yahoo.com/s/nm/20070424/sc_nm/space_planet_dc
http://www.space.com/scienceastronomy/070424_hab_exoplanet.html
http://www.world-science.net/othernews/070425-habitable-planet.htm
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/04/24/BAG33PE14U26.DTL