[Space] Gliese 581

[RyanW]

Originally Posted by David Johnston2

Odds are that any land life would have some ability to retreat underground to protect itself from solar flares.

I don't think there is any evidence of GL 581 being a flare star. It is classified as a BY variable, but the variance is so small it isn't clear that it isn't just measurement errors.

Of course, being closer to its sun, even "normal" solar activity may have a bigger impact.

[David Johnston2]

Originally Posted by RyanW

I don't think there is any evidence of GL 581 being a flare star. It is classified as a BY variable, but the variance is so small it isn't clear that it isn't just measurement errors.

Of course, being closer to its sun, even "normal" solar activity may have a bigger impact.

Every red dwarf except for the most senile has dangerous flare activity for anything in the liquid water zone.

[dataweaver]

Originally Posted by Fred Brackin

The article Dataweaver linked to put the mass of d much higher than that. At least 5.8 earth masses. It's right at the outer limit of the liquid water zone and no statement about it not being tide-locked was included.

d is indeed right at the outer edge, and from what I recall, c is just inside the inner edge; both were earlier candidates for consideration of habitability, but have largely been rejected due to their borderline conditions (suggestions being that they're probably Venus-like and Mars-like, respectively).

But the one to watch is g. g is new on the scene, having been discovered a few days ago (Sept 29); it is nestled between c and d, placing it comfortably near the center of the liquid water zone. c and d are estimated at roughly 5.6 earth masses each; g weighs in at 3.1 Earth masses. It may mass more (as may the other two) by up to twice the stated masses, assuming the planetary system to be stable; but the masses are most likely to be close to the given lower limits. Of all of the extrasolar planets discovered to date, g has the best shot at being habitable.

Oh, and one of its discoverers has nicknamed it "Zarmina", his wife's name.

[dataweaver]

Originally Posted by David Johnston2

Odds are that any land life would have some ability to retreat underground to protect itself from solar flares.

...assuming that the world doesn't have a decent magnetospere to protect it against solar flares. That said, given that Zarmina rotates on its axis once every 37 days or so (given tidal locking), that's probably a safe assumption. I think. But then, I also expected that winds would likely be rough; apparently, that may not be the case after all.

[Fred Brackin]

Originally Posted by combatmedic

Fred, assuming that it is possible that the atmosphere of the newly discovered planet isn't like that of Venus, what sort of life do you think might develop there?
Or is any talk of life on the planet just wishful thinking, IYO?

All other things being equal I believe that the red-dominant spectrum of the star gives you less energy for photosythesis. That's just less input at the base of the life cycle.

Then you add in that the only proposal for adequately cooling the dayside involves perpetual hurricane force winds.

Firstly we need this everlasting storm to not make much in the way of clouds and exacerbate our cool sunlight problem.

This seems a little unlikely to me but the longest I ever spent under hurricane force winds was about 48 hours. We had darkness at high noon while that happened though.

If there was little water in the atmosphere this problem might not be as bad as it would be on Earth but low moisture makes other things worse.

Then you add in that there might be little topsoil. The winds would probably blow it away before it could accumulate.

For an optimum everything-works-as-well-as-possible scenario I'm getting slow-growing rock-hugging lichen-like plants as the main probability for any sort of life based on an Earth-like photosynthesis cycle.

Technically, the majority of Earth's biomass might be anaerobic bacteria living in porous rocks down to a surprising depth. You could have that here but it's kind of a dead end for rpg scenarios. There are probably long-term issues for the planet's carbon cycle too. Solvable but not ignorable IMHO.

Maybe this planet could have a thriving ecology that was radically different from anything Earth-like. All I can suggest is that you bring lots of handwavium and do like Doc Smith did and don't go into much detail about the basis of the ecology on Trenco. :)

[dataweaver]

Originally Posted by Fred Brackin

All other things being equal I believe that the red-dominant spectrum of the star gives you less energy for photosythesis. That's just less input at the base of the life cycle.

True enough.

Originally Posted by Fred Brackin

Then you add in that the only proposal for adequately cooling the dayside involves perpetual hurricane force winds.

It turns out that I probably overstated this; one of the planet's discoverers has pointed out that to properly redistribute the heat you can get by with dayside wind speeds somewhere around 40 mph or so; not exactly a gentle breeze, but not hurricane strength either.

[David Johnston2]

I kind of wish that GURPS Space wasn't so limited in the maximum possible mass of a randomly generated planet. While obviously the extrasolar rocky planets we find are going to be the very largest ones, there's still no way to randomly generate them.

[gjc8]

Originally Posted by Fred Brackin

All other things being equal I believe that the red-dominant spectrum of the star gives you less energy for photosythesis. That's just less input at the base of the life cycle.

Hang on. Other things equal, yes a red (cool) star will put out less energy, but the habitable zone is closer to the star. The energy flux received by a planet in the habitable zone has to be about the same, regardless of stellar spectrum, because they'd all be about the same temperature (that being the definition of the habitable zone). Or am I missing something?

Now, there may be other problems. Cooler temperature means the black-body spectrum is broader, so it may not be possible to capture as great a fraction as is possible for G-class stars. Also, each photon is lower energy, so you may have work-function problems. Is this what you mean?

[Fred Brackin]

Originally Posted by gjc8

Or am I missing something?

Yeah, it isn't about gross energy. It's the specific form of that energy.

The spectrum of a red dwarf peaks at a much lower place than the spectrum of a G2 like out sun. A greater proportion of the light is red at the bottom of the visual spectrum and a lower proportion are yellow to blue photons with higher energy than red photons.

These higher energy photons cause photosynthesis with greater efficiency. Photosynthesis works on a one photon at a time basis.

Also look at the big quote on this page in the post by strefanj.....

http://forums.sjgames.com/showthread.php?t=73515&page=2

.....the scientist there says that the reddish light is better at transmitting simple warmth than a spectrum like the one we're used to. He calculated insolation (more or less total solar energy received) at 60% of Earth.

So less light and lower photosynthetic efficiency (and that is basically unavoidable with lower energy photons) means less energy pumped in at the base of the ecology. That very likely means less biomass and a slower rate of production for that biomass.

I am also quite concerned about clouds, both water vapor clouds and dust ones. That could significantly reduce the amount of light reaching the surface and make bad matters worse for Earth-like life.

I am also concerned about the density and composition. Greater than Earth mass but similar density likely means more vulcanism. That would mean more CO2 in the atmosphere and even more chance for a runaway greenhouse.

Non-Earth-like composition and density just makes things alien.

What was said in the link above about greater likelihood of retaining primordial atmosphere and less chance of losing atmosphere in late collisions (see articles related to formation of Earth's Moon) add to the greenhouse worries.

I wouldn't set really high probabilities on any specific outcome but my highest probability would be that we've found a super-Venus rather than a variant Earth.

Radically unEarth-like ecologies and life might well be possible but no one here (and I mean this planet) could tell you much that was significant about these possibilities. It would be unknown almost by definition.

[Sunrunners_Fire]

I'd wait for information on atmospheric composition before attempting to guess at any ecology. If it has measurable atmospheric oxygen, well ...

I would also note that we have multiple types of infrared-specific photosynthetic bacteria (and plankton) in the here and now. One type of which we've done up a full DNA map / sequencing for the purpose of transferring that capability into more complex plants to increase photosynthesis efficiency. GMOs are so fun. :)