Gliese 581c, the smallest exoplanet yet discovered at just five earth masses, may be too warm to support liquid water. Scientific excitement over the discovery of the planet was palpable as the planet orbits within its star's habitable zone, leading to speculation that it might harbor liquid water and be a viable candidate in the search for extra-terrestrial life. However, it appears the planet may be too warm due to an atmosphere rich in carbon dioxide and methane, leading to a runaway greenhouse effect such as that found in our own solar system on the planet Venus.
"Of the more than 200 extrasolar planets, or "exoplanets," discovered since 1995, Gliese 581c was the first found that resides within the habitable zone of its star, if only barely. The habitable, or "Goldilocks" zone is the region around a star where the temperature is neither too hot nor too cold, so water can exist on a planet's surface in its liquid state. Water is a key ingredient for life as we know it.
But new simulations of the climate on Gliese 581c created by Werner von Bloh of the Institute for Climate Impact Research in Germany and his team suggest the planet is no Earthly paradise, but rather a faraway Venus, where carbon dioxide and methane in the atmosphere create a runaway greenhouse effect that warms the planet well above 212 degrees Fahrenheit (100 Celsius), boiling away liquid water and with it any promise of life."
However, those same greenhouse conditions found on Gliese 581c may also hold sway on sister planet Gliese 581d, possilby allowing for liquid water there. At eight earth masses, 581d is the second smallest planet yet found. This new data point out that the atmospheric conditions of these distant planets have to also be taken into account when searching for potential life bearing planets. One other item that leads scientists to believe there could be alien life forms in the system is that the star is relatively old and has been quite stable over the period it has been observed.