Ocean Planets?

Another article trawled from New Scientist — about ocean planets around red giant stars.

The initial picture this article paints in your mind is quite a poetic one. As a star leaves the main sequence and starts to swell into a red giant, it warms the outer reaches of it’s planetary system. Heated by the star’s increased infrared output, large icy planets start to thaw out, evolving into ocean worlds. Watery footholds for life, bathed in deep red sunlight.


EDIT– Actually, I retract my earlier remarks about their proposed mechanisms. As it turns out, I’m rubbish at Geochemistry, as explained in the comments. With thanks to ranka for setting me straight.

It is heartening to learn that predictions indicate a planet could stay in a red giant’s habitable zone for up to 3.7 billion years. Given that the oldest fossils found on land are around 3 billion years old, this gives a fair amount of hope that life could evolve on such a world. Though it’s also sad in a way. Such life evolving around a dying star… A civillization like ours might have just enough time to develop to a state to realise that they were doomed.
(There’s a sci-fi novel in there somewhere.)

I must say though, I’m not sure I agree with the obligatory outside opinion…

But James Kasting of Pennsylvania State University, who was not involved in either study, questions the assumptions underlying the new calculations, including setting the optimal temperature for photosynthesis-based life at 50° C, halfway between boiling and freezing.

“50° C would be almost uninhabitable for anything that lives on Earth except for some kinds of bacteria,” he says, pointing out that Earth’s average surface temperature is around 15° C.

Yes indeed it would be uninhabitable for most life that lives on Earth. But we’re not talking about Earth. We’re talking about a different planet, with life that had evolved to live there. Having specialised to exist at such temperatures, such life would likely have an altogether different biochemistry.

Besides, life is tougher than most people think.

All that said, I’d certainly be intent on red giants being included in the searches for habitable planets. Not least because of the implications that might have for astrobiology as a whole!

The actual paper behind this article has yet to fall into my hands, and I suspect it may have been misconstrued in places, but I fear I’d probably resign it to being another of those nice ideas that doesn’t seem as well though out as it could be.

But then, I’m no expert.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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