Saturday, 2 October 2010

Gliese 581g is an Earth-like exoplanet – or perhaps not

In 2007 Gliese 581c, the sister planet of the new ”Goldilocks planet” caused a disappointment to those who were hoping to find life in outer space. Image courtesy of ESO.

Joel Kontinen

The discovery of a potentially habitable planet has made lively headlines in the popular media. It might be good to remember that the sister planet of 581g caused a considerable amount of excitement in 2007. Later, however, researchers found out that the planet named Gliese 581c was probably as warm as Venus.

Steve Vogt of the University of California Santa Cruz, who was a member of the research group that discovered Gliese 581g, says, ”Our findings offer a very compelling case for a potentially habitable planet." He was quoted as saying that he is 100 per cent sure of ”the chances of life” on the planet.

Gliese 581g orbits a red dwarf twenty light years from Earth. Red dwarfs are known to be unstable and Gliese 581g orbits it closer than Mercury our sun.

It is a world of extremes. One side of the tidally locked planet faces the sun perpetually, while the other is in darkness. The planet has a mass of 3 – 4 Earths and its temperature is expected to range from around + 71 degrees Celsius (160 degrees Fahrenheit) on the sunny side to -34 degrees Celsius ( - 29 degrees Fahrenheit) on the dark side. The habitable zone is assumed to lie in between these two extreme areas.

Jay Richards, who co-authored the book The Privileged Planet with Guillermo Gonzalez, takes a critical approach to this claim:

The planet in question is tidally locked, so the same face perpetually faces its star. So it won't have a pleasing climate. It's about three times more massive than Earth, and it's quite close to its star, which is an M dwarf. Such stars are probably not good hosts for habitable planets due to their high activity levels…

Venus and Mars are much more Earth-like that this or any other extrasolar planet we've yet been able to detect. For instance, they're around a star known to host a habitable planet, and they're both quite close in orbit to that habitable planet. And yet, neither is home to life of any sort

While Gliese 581g might orbit its sun within the Goldilocks or habitable zone, this does not necessarily mean that the planet is habitable. Plate tectonics and a big moon would also be necessary for life. Doctor Don DeYoung has shown that if the Earth did not have a sizeable Moon, there would be no tides, the oceans would be stagnant and marine life would die.

Recently, New Scientist disclosed that the birth of the Moon was one of the ”ten accidents that made us”.

According to Genesis, the Moon is not the result of a lucky accident but of a definite act of creation. In contrast, we do not know whether Gliese 581g has any kind of moon, so the joy of Vogt and colleagues might be a bit premature.


Alleyne, Richard. 2010. Gliese 581g: the most Earth like planet yet discovered. Telegraph. co. (29 September)

DeYoung, Don. 2006. Our Created Moon. Answers in Genesis DVD.

Richards, Jay. 2010. Science Reporters Should Quit Crying "Life!" (30 September).