Tuesday, December 06, 2011


Is Kepler 22-b a "New Earth"?! A New Neptune, Maybe...

First the data on the recently discovered planet 'Kepler 22-b':

"To date, its mass and surface composition remain unknown. If it has an Earth-like density (5.515 g/cm3) then it would mass 13.8 (2.43) Earths while its surface gravity would be 2.4 times Earth's. If it has water like density (1 g/cm3) then it would mass 2.5 (13.8/5.5) Earths and have a surface gravity of 0.43 (2.5/2.42) Earth's. The distance from Kepler-22b to its star is about 15% less than the distance from Earth to the Sun. Its orbit is about 85% as large as Earth's orbit. One orbital revolution around its star takes 289.9 days. The light output of Kepler-22b's star is about 25% less than that of the Sun. The combination of a shorter distance from the star and a lower light output are consistent with a moderate surface temperature. Scientists estimate that in the absence of atmosphere, the equilibrium temperature would be approximately -11°C. If the greenhouse effect caused by the atmosphere is Earthlike, this corresponds to approximately 22 °C (72°F) average surface temperature." - Wikipedia (my italics)

""This is a major milestone on the road to finding Earth's twin," said Douglas Hudgins, Kepler program scientist at Nasa headquarters in Washington." - www.guardian.co.uk/science/2011/dec/05/exoplanet-kepler-22-b-nasa-earth (my italics)

So, not Earth's twin then, as one might think from the media hype.

"In another step towards finding Earth-like planets that may hold life, NASA said on Monday that the Kepler space telescope had confirmed its first-ever planet in a habitable zone outside our solar system... Kepler-22b is 2.4 times the size of the Earth, putting it in a class known as "super-Earths", and orbits its sun-like star every 290 days. Its near-surface temperature is presumed to be about 22 degrees Celsius. Scientists do not know, however, whether the planet is rocky, gaseous or liquid." - www.smh.com.au/technology/sci-tech/nasa-confirms-superearth-that-could-hold-life-20111206-1ofx3.html (my italics)

"The planet itself is 2.4 times the size of Earth, but that’s about all that is known about Kepler-22b. Its mass/composition is unclear at this point, meaning it could be a “global ocean” or entirely rocky." - www.dailytech.com

So, its not an Earth-like planet that may hold life, but a step on the way to finding such. We do not know if it is a chunk of rock, or a ball of gas or a liquid ocean.

"The only trouble is the planet’s a bit big for life to exist on the surface. The planet is about 2.4 times the size of Earth. It could be more like the gas-and-liquid Neptune with only a rocky core and mostly ocean... Because its size implies that it’s closer to Neptune in composition than Earth, “I would bet my telescope that there is no hard, rocky surface to walk on”..." - www.washingtonpost.com/politics/a-new-earth-nasa-finds-planet-outside-solar-system-at-comfy-72-degrees-with-sunlike-star/2011/12/05/gIQA3Z0fWO_story.html?tid=pm_pop (my italics)

‘Kepler's scientists said they've confirmed the existence of their first exoplanet solidly within the habitable zone of its solar system, where water could exist in liquid form at a pleasant 72 degrees Fahrenheit (22 degrees Celsius). That certainly sounds livable, but Mendez told me that the planet, known as Kepler-22b, doesn't quite fit into the sweet spot for habitability because it's closer in size to Neptune than to Earth. "I confirmed its radius, and Kepler-22b is a low-end Warm Neptunian, very close to a Superterran," Mendez said in a Twitter back-and-forth from NASA's Ames Research Center in California, where he was presenting his research at the Kepler Science Conference. Neptunians are likely to have a gaseous rather than a rocky composition, which might make it tough for life as we know it on Kepler-22b.’ – ‘Alien Planets get Pidgeonholed’, Alan Boyle http://cosmiclog.msnbc.msn.com/_news/2011/12/05/9233790-alien-planets-get-pigeonholed (my italics)

In sum: Kepler 22-b is 'a bit big for life to exist on the surface', if it even has a solid surface! Moreover, we don't know whether or not Kepler 22-b has water, although if it does have water then it would be liquid (because it's in the goldilocks zone around its star). However, even if there is water on Kepler 22-b, water is a necessary but not a sufficient condition for life. Kepler 22-b is probably more like Neptune than Earth. Neptune isn't well known for its wildlife.

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