Sep 30, 2008

A Gas Giant At Epsilon Eridani May Harbor Life On Its Moons

Epsilon Eridani is a star only 10 light years away. It is known to have at least one and possibly several planets, one of which is thought to be similar to Jupiter. And now an astronomer suggests that its moons may be in an excellent position to have extraterrestrial life on them!

(Artist’s conception of the Epsilon Eridani system courtesy of CosmicRAY.)

Ray Villard, a blogger at Discovery Channel’s CosmicRAY blog and head of the Hubble Space Telescope’s Public Information Office, has pointed out an exciting fact. One of the explanets around Epsilon Eridani has an orbit which is quite conducive to the formation and survival of life as we know it. The reason has to do with the orbit of the planet and the nature of the star itself. Here’s the skinny (orbital schematic courtesy of Extrasolar Visions):

Epsilon Eridani is a K2 class star; our sun Sol is a G2 class star. These two classes are very similar; thus a planet orbiting within 1 astronomical unit (AU) of Epsilon Eridani could expect to have conditions similar to those of Earth. It turns out Epsilon Eridani B, the only confirmed explanet in the system, does just that. But unfortunately, there is a catch. Epsilon Eridani B has an eccentric orbit, periodicity of 0.7, the most eccentric orbit of any known exoplanet in fact. What does this mean? It means that the planet swings from a distance of about 1 AU to a distance of over 5 AU every 8 years or so. (5 AU is the distance of Jupiter from our sun.) So while a moon of the world might be nice and comfy for part of its year, it would get very cold and dark for a longer part. This is not a good thing for earth-type life!


If the moon had an atmosphere like Venus‘, then much heat would be trapped and not lost during the colder part of the orbit. And computer models show that it is entirely possible for the mass surrounding a Jovian-class exoplanet to coalesce into a single, Mars-sized world that could hold a significant atmosphere. Also, life can exist at much more extreme conditions than previously thought. So the bottom line is that this planet, if it does indeed have a moon of the right type, could definitely be a target for exobiologists once the technology is available to study it.

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