[Space] Gliese 581
 

Anyone interested in seeing and/or writing up the Gliest 581 system to campaign-ready stats?

Re: [Space] Gliese 581
 

The tidal locking on Gliese 581g greatly reduces its' interest level for Terran explorers. That would limit the liquid water (at best) to a twilight area around the planet's terminator.

Rather than an unusually dynamic atmosphere with perpetual winds sweeping from a too hot perpetual dayside to a too cold eternal nightside, I suspect you would actually see some sort of static Venusian atmosphere.

Some future astronomical project might be able to confirm this by getting a too strong Co2 spectrum from the the planet.

So just personally I would not rush to write this place up as the target for Man's first extra-solar colonization effort or similar rpg scenario.

To the best of my understanding the habitable zone of any M-class dwarf is going to be filled with tidally locked worlds. You'd need some sort of exotic scenario such as a double planet system tidally locked to each other but still spinning relative to the star or something like that.

Re: [Space] Gliese 581
 

There's reason to think that an atmosphere that's thin enough to breathe would still be thick enough to redistribute the solar heating more or less evenly (see here); it needn't be coupled with runaway greenhouse warming, as per Venus. An atmosphere as thin as a tenth of an atm might be sufficient for evening out the temperatures, given appropriate levels of carbon dioxide and water vapor.

Part of the point of the above research paper is that tidal locking isn't necessarily as much of an obstacle to habitability as has previously been supposed - at least, not in the ways traditionally depicted. With a sufficiently thick atmosphere, you're likely to trade off the "day side is baked, night side is frozen" problem for one of "temperatures are relatively even, but you have to deal with constant gale-force winds": I've seen a description of this scenario as the world having a persistent hurricane with its eye centered on the sun-pole. Habitability would depend on how large the hurricane tends to be.

As for exotic double-planet scenarios, it's very likely that the same tidal forces that result in an individual planet becoming tide-locked would split up a binary pair of planets in short order; it's the same reason why we can reasonably assume that a tidally locked world won't have any moons to speak of. A gas giant might get away with keeping some satellites; but I doubt that anything smaller would.

Re: [Space] Gliese 581
 

A resonant rotation can also result. If in a 3:2 resonance, a planet would have a "day" that was twice the length of the year.

I believe the exact mechanism of Mercury's resonance isn't perfectly understood, though, and without a Jupiter-scale gas giant it might not happen.

Re: [Space] Gliese 581
 

Plus Gliese 581 d is also around 3 earth masses, in the goldilocks zone, and not tidelocked.

Re: [Space] Gliese 581
 

Mercury's resonance depends on it having a highly elliptical orbit; Gliese 581 g appears to have no ellipticity to speak of. And as far as we can tell, it probably is tidally locked, unless something strange is happening.

Really though, I was wondering what we could come up with by taking the solar and planetary data that we know about (the latter essentially being estimates of each planet's mass, distance from primary, and ellipticity) and plugging them into GURPS Space's planetary design system. Can the book handle them? If so, how interesting can we reasonably make the resulting system? In terms of g in particular, can it be made habitable without unduly stretching the existing numbers? The fact that it's nominally in the biozone is a step in that direction; but is it enough?

Re: [Space] Gliese 581
 

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.

Do you have a source for your variant data?

Re: [Space] Gliese 581
 

No, I just misremembered. Ignore me.

Re: [Space] Gliese 581
 

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?

Re: [Space] Gliese 581
 

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