Its life Jim, but…

Posted on November 21, 2011


Gliese 581g

Gliese 581g

These days it seems that the harder we look for life the more we find it can turn up in the most unlikely of places. Here on Earth, we appear to have found it everywhere we look but even out in the wider galaxy science is leading us to places for life that were previously thought to be impossible.

Vi-Star-sizes

Star sizes

One such place is planets buzzing around the small, cool and red suns known as red dwarfs which – small and cool though they may be – are by far the most common kind of star out there. Now, it appears that even the relatively far-off icy planets that can orbit these tiny stars can be host to living organisms. The key, as it seems to be everywhere on Earth, is liquid water which it now seems could exist even on the chilly, distant planets around a red dwarf star because of the way that snow and ice absorb the near-infgrared light radiated by such stars.

Habitable Zones

The very narrow “Goldilocks Zone” for free liquid water that can exist neither frozen nor boiled off around a red dwarf is such that solar gravitation on these planets would be much stronger than here on Earth and could even result in tidal locking of the planet, meaning one side would be constantly facing toward the tiny star and the other constantly turned away. While being so close should make such planets easier to spot, they also face the risk that red dwarfs tend to flare up and scorch the surface of any nearby planets – not the best of things for any life struggling along on the surface!

Further away though, it had been thought that the planets around a red dwarf would be too cold, but now work by Manoj Joshi of the University of Reading in the UK and Robert Haberle of NASA’s Ames Research Centre in California have shown how even such far-off planets could be warmed enough for life to gain a foothold. Details of the paper can be found at Springerlink but in simple terms it comes down to the reflectivity of snow and ice.

Here on Earth, about 50 to 80 percent of the solar visible light is bounced right back into space by snow and ice which consequently stays frozen. Red dwarf stars, on the other hand, shine less in visible light but much more in the near-infrared which ice and snow soak up rather than reflect. Which makes it, of course, hotter than otherwise. In the case of Gliese 436 and 1214, both red dwarfs with known exoplanets, the reflection is as little as 10 to 40 percent which extends the habitable zone by 10 to 30 percent.

The full work will in due course be published in Astrobiology.

Advertisements