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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5 Responses to Ocean Planets?

  1. Yeah, CO2 would never be completely absent from the atmosphere, but it could get the point where it’s removed almost as fast as it enters the atmosphere. (Actually, I do wonder if, in the situation of a planet with extremely low CO2, if plants might evolve some way to “recycle” the CO2 they produce by respiration, much as many animals recapture water produced by metabolism)
    And, yeah, life would survive longer than just plants. The last living things on Earth would, presumably, be bacteria, as Earth is slowly boiled.
    I do wonder, though, if a sufficiently advanced technology would be able to actually move Earth outward in its orbit, to prolong the existence of life. Given the hundreds of millions of years it’ll take for the Sun’s warming to be a problem, that should be quite possible. :-) Even if humans wipe themselves out, something else might evolve in that time (and be quite astonished when they reach the Moon and find our abandoned equipment!)
    The Life and Death of Planet Earth is a good discussion of Earth’s fate, if you’re interested.

  2. invaderxan says:

    Maybe it’s not simply that we’re afraid of the unknown. Maybe we’re actually afraid of not knowing.
    …if you see what I mean. :)
    I, for one, am still quite optimistic that we might discover life out in space somewhere. Frankly, I’m still not convinced we’re entirely alone in our own solar system…
    But then, maybe we haven’t found life elsewhere yet, because we’re not sure what we’re supposed to be looking for. It seems unlikely that several billion years of complete isolation would give rise to anything Earthlike. That would be like asking two people in different parts of the world to each draw a picture and then expect both pictures to be the same. For a start, they’d probably use different canvasses…

  3. invaderxan says:

    Interesting, interesting… Thank you for setting me straight on that. I guess geochemistry isn’t one of my stronger points. :)
    It’s worth noting, however, that all macroscopic life (at least on Earth) respires. Even plants take in oxygen and breathe out CO2. Surely the only scenario which would kill off plants would be one where both CO2 and oxygen were depleted, leaving a relatively inert nitrogen atmosphere.
    The question is (regardless of what planet we’re talking about), should such an ecological catastrophe ever occur, what other life forms might expand their territory to fill the missing niches. Life seemingly has a habit of colnising any space available to it…

  4. Actually, that does make sense. Carbon dioxide levels in our atmosphere are regulated, in part, through a feedback loop. CO2 is added through volcanism, while it’s removed by rainwater eroding calcium-containing rocks, to form limestone. This is why exposed rocks are necessary. Rocks under the sea don’t erode nearly as much, thus, once their surface layer has reacted with dissolved CO2, the process stops. But rocks on land erode away, constantly exposing new calcium-containing rocks. Anyways, higher temperatures lead to greater evaporation, greater rainfall, faster erosion rates, faster removal of CO2. Lower temperatures have the opposite effect. This process has allowed Earth’s temperature to remain relatively stable despite the Sun’s warming, through the gradual decline in CO2 (indeed, Earth is currently in a relatively cool phase compared to much of the Earth’s past). Eventually, a few hundred million years from now, CO2 levels will decline to a level too low to allow photosynthesis. Exactly when that will happen is unknown, in part because we don’t know to what extent plants can evolve to cope with declining availability of carbon.
    Of course, when it comes to alien worlds, there’s a much bigger question. We have no idea what could-have-been forms of life were pre-empted by Earth life, or even were impossible in Earth conditions.

  5. nimblenimbus says:

    I’m by no means an informed person in matters of science, because I am just a student, and what do I know? But I agree with you in regards to what you said about the biochemistry of potential life in other realms. What we know, as much as we know and claim to know about science and evolution and biology in general, when it comes to the expanses of the universe and things altogether foreign to us, we really do know basically nothing.
    It is a huge step to assume that things probably couldn’t survive on a given area just because something couldn’t live here. We pretty much don’t know ANYTHING. At all.
    I always thought people were just afraid of the unknown. People are afraid of the fact that when it comes to matters like this, we have absolutely no way of even beginning to understand how life could exist somewhere else, much less the science of such things. We can hardly even master our own planet, let alone begin to understand the universe. :]
    Of course, everybody knows more than they do. There’s some saying or another along the lines of those who claim to know the most are actually the least informed… I think it was Socrates. Maybe the guy in that quote is just afraid to admit that humans really have no idea about stuff like this. :P
    Even if it is out there, though… I really doubt we’re ever going to find it. At least not soon.

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