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Thursday, April 26, 2007


Gliese 581 c, Our First Terrestrial Exoplanet

When I was in high school, my biology teacher asked us to imagine life of a tidally locked world. I had great fun, imagining the creatures that lived in the baking deserts under the perpetual Sun. The frozen wastes under perpetual night, and the twilight zones, where more kind conditions reigned.

The report from the ESO of a world such as my high school project world, a tidally locked planet orbiting the red dwarf Gliese 581 20.4 light years away, has captured the imagination of many people (heck! Wikipedias fast! there are already entries for Gliese 581 c and Gliese 581 d). As well as the Bad Astronomer, Stuart and Tom discuss this find, each with a different point of view. What's more, it has turned up as major articles in the newspapers, the Australian, The Age and even the local Advertiser (no online story, sorry). The journal Nature has a report, as does ABC science, and there is a video interview on Lateline.

One thing that gets overlooked a bit is that the new planet is part of a solar system, there are three worlds in this system, a 15 Earth Mass Neptune-like planet (Gliese 581 b) and an 8 Earth mass planet (Gliese 581 d). This solar system doesn't look much like ours though, Gliese 581 b screams round its Sun in 5.4 days, Gliese 581 c has a 12 day long year.

But this is what makes this system so important. Most of the exoplanets seen so far are "Hot Jupiters". Massive worlds close to their Suns. Our current theories of planet formation say that these worlds form out beyond the "frost line", the distance from the Sun where ice forms, and then migrated inwards. In most of these models, any terrestrial worlds get ejected or consumed by the giant worlds.

More recent models suggest that terrestrial worlds can re-form after the Giants move through. This finding of a terrestrial style world (1.5 Earth radii in diameter) outside a star hugging giant world suggests these models are plausible, and there maybe a lot more Earth- like worlds than we suspected around systems with hot Jupiters.

The Universe has just become a more interesting place.

I'll be making a Celestial file for this system soon.

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