We found one!

[steuard]

Wow oh wow. Universe Today just posted an article about an Earth-like planet discovered around a nearby red dwarf star. (The original source appears to be a UC Santa Cruz press release.)

It's right in the star's "habitable zone" (which mostly means "right temperature for liquid water") and has a mass about 3-4 times Earth's, so a quick estimate is that gravity there might be about 40% stronger than here (it wouldn't be too different than standing in an elevator as it gets going). That's plenty to hold an atmosphere. The planet has its quirks, of course: it's close to its cool sun, so a full orbit only takes about a month. Also, like our Moon it always has the same side facing "in": a planet of eternal sunlight on one side and eternal shadow on the other. Naturally, the only comfortable places to live would be in the twilight region encircling the planet between the extremes of hot and cold, where the red sun burns forever on the horizon.

This is awesome. And it's sooner than most people expected to find something like this, which may mean that planets like ours really are pretty common after all!

Now if only we could find a way to get there.

Comments

[lordhylas.livejournal.com]

Think of the winds generated by the temperature gradient.

[kirin]

I'm really not sure how that would work when the temperature distribution is relatively stable. Obviously you can't have continuous net wind from one pole towards the other...

[steuard.livejournal.com]

Yeah, and the worst case scenario is that the winds carry air to the frigid pole of the planet where it's cold enough that the atmospheric gasses condense and never return to the hot side: you'd wind up with no active atmosphere at all. Or even if the N_2 and O_2 didn't freeze out, all of the water would wind up frozen on the dark side and the planet as a whole would be bone dry.

But it's possible that the heat transport involved with those winds would prevent the worst of that from happening. It's remarkably hard to simulate such things!

[lordhylas.livejournal.com]

Why can't we model it? It seems like it would be a much simpler model than, oh, Earth, with our varying heat input.

For the model of this, we could start with a spherical mass of uniform temperature air. Insert an insulator in the middle of it (the planetary mass would serve as an insulator, no?). Introduce a single heat source on one side to serve as the solar input. And there we go. If we later want to account for vapor cooling (for liquid water that might exist in the twilight zone), we can add that in that region, but we at least have a start with this admittedly very simplistic model. Maybe volcanism would further complicate the model.

But I think that, with the heat input on the day side, and the very cold night side, if there is an atmosphere, then, thermodynamically, there *has* to be heat flow from the hot side to he cold side, which means wind. And the more extreme the temperature difference between the day and night sides, the higher the winds, no?

[steuard.livejournal.com]

My impression is that a fairly basic model isn't too hard, but that basic models by and large wind up with the atmosphere (or at least all its water) freezing out on the cold side, and that's the end of that. I haven't studied this much at all, but most of the ideas that I've heard of for avoiding that fate rely on nonlinear effects in the atmosphere (or in the oceans, if there are any) to make the heat redistribution work. (One model suggested that liquid water might be able to flow from the hot side to the cold side even underneath a thick ice layer, which might be enough to prevent the worst of the effects.)

Maybe it's not actually as complicated as it sounds, but it's certainly intimidating to me!

[lordhylas.livejournal.com]

Well, a tide-locked planet like this has been the stuff of many a science fiction story. Now perhaps with enough study we can answer those speculations. But we will need better resolution telescopes first. Heck, we don't even know if it even *has* an atmosphere yet. We need some spectroscopy for that. But that can give us a *lot* of info.

[akjdg.livejournal.com]

The propensity for a planet that is tidally locked to its star being conducive to the rise of life is an interesting question. The weather patterns in the atmosphere would be the first question. Assuming the atmosphere didn't all condense on the cold side (and perhaps some gas would remain bouncing around the terminator at least), the convective currents along the terminator would be something. Lots of dramatic thunderstorm-type events, perhaps.

If the planet was endowed with a lot of water, and that did transport to the dark side, you would expect liquid phase water at the base of glaciers (due to pressure and/or geothermal heat). Would such a planet tend to be tectonically dead or alive? If the gravitational lock is anything like the Earth-moon system, that will help drive tectonics and keep some heat about on the dark side.

Also, isn't the Earth's strong geomagnetic field important to the retention of our atmosphere? Perhaps the solar wind from a red dwarf is weaker than from our sun, but an actively circulating planetary core seems pretty important to a stable atmosphere. Especially if one side of the planet is extremely hot.