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Comment by taliesinb | Hacker News Reader

Wow, amazing result. And talk about synchronicity - just last night I watched an interesting 2015 talk about the search for planets around Alpha Centauri using the radial velocity technique: https://www.youtube.com/watch?v=eieBXGpNYyE

The speaker even mentioned the previous incorrect HARPS announcement, which was later found to be an artefact due to the windowing function they used - a pretty embarrassing mistake. This new finding involves a completely different period: 11.2 days instead of the previous 3.24 day signal.

Also, link to the Nature paper for the lazy: http://www.eso.org/public/archives/releases/sciencepapers/es...

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If you mean the previous claim of there being an Alpha Centauri Bb planet, later retracted, then this new finding involves a completely different star, not just a different period.

This is around Proxima Centauri, the previous one was around Alpha Centauri B. Proxima is a really really small red dwarf, just 12.3% the mass of sun, while Alpha Centauri B is a K-type star, ie somewhat smaller than sun but not that much; around 90% of Sun's mass (And there's also Alpha Centauri A, 10% more massive than the sun). We're not even 100% sure that Proxima is part of the Alpha Centauri system, though I gather it's considered highly likely - it's pretty distant from the Alpha Centauri system, some 15 000 AU (1 AU = distance between Sun and Earth), almost a quarter of a light year.

Yes, realized this and was editing my comment to reflect that but you beat me to it :). They did mention a previous signal from 2013, which got me confused with the spurious signal the SETI lecture mentioned.

heh, as you say; apparently there was a previous signal; reading the article about the find at centauri dreams, http://www.centauri-dreams.org/?p=36210 - and it does mention a pre-2016 Doppler signal with a period of 11.2 days around specifically Proxima, that was unconfirmed, and that this mission was to investigate that more closely. "The HARPS Pale Red Dot campaign was created to confirm or refute this 11.2-day signal"

I'm just not sure if that's what the speaker in your video was talking about, of if the embarrasing mistake that was actually announced was the Alpha Centauri Bb planet (or maybe there were other candidates I didn't hear about); I'm gonna watch the lecture you linked and see. Thx for an interesting link, btw!

If the period is 11.2 days, seems like there is a high chance that it is tidally locked to the star. If that's the case, that side is probably pretty roasting hot, the other quite cool. But maybe life near the edge is OK. Probably some interesting weather patterns there as well.

Probably some interesting weather patterns there as well.

If by "interesting" you mean constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.

Before there was soil, or sky, or any green thing, there was only the gaping abyss of Ginnungagap. This chaos of perfect silence and darkness lay between the homeland of elemental fire, Muspelheim, and the homeland of elemental ice, Niflheim.

http://norse-mythology.org/tales/norse-creation-myth/

Perhaps it could be "the chaos of perfect silence," because the wind noises generated would render any unprotected human ears deaf within minutes?

Hmmm. We can generate heat and light using electricity, and we can generate electricity using windmills. Could we perhaps inhabit the dark side of a planet like this by building really sturdy windmills to harness those constant winds and then building an insulated, heated, artificially lit structure to grow plants and live in?

I can only see geothermal energy working effectively

We can build thermal powerplants on the edge and live off the temperature gradient. Either use Seebeck effect or just steam turbines.

...constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.

Seems like this would allow surface habitation some way onto the bright side. Wind at the surface would be blowing from cold to hot, with the return at some altitude.

> If by "interesting" you mean constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.

Hey, at least it's a short walk between cooking your food and icing your drink!

Its a really really tiny star; quite small even as M-dwarfs go. So its habitable zone cannot but be where it could tidally lock the planet. Now, maybe some other resonances are possible, perhaps if there are other bigger planets around it helps (and I think they didn't exclude something up to a size of Neptune at about 1AU or beyond); don't know how the orbital mechanics of all this work out.

But there were various modelling attempts to see how a tidal lock affects the climate, and it may not be a dealbreaker; not too thick an atmosphere could effectively transport that heat around, at least so that it doesn't risk freezing the atmosphere on the dark side and making it uninhabitable. But its just modelling so..

Maybe even more problematic is that a tidal lock could imply no internal dynamo, and so no protective magnetic field, and Proxima flares quite a lot, so it could have totally eroded its atmosphere and sterilized the surface with UV etc. Plus Proxima was much much hotter early on; would that period have permanently made the planet uninhabitable?

We just know so very little about habitability of M-dwarfs, and particullary the really small ones; we'll just have to find out,

Before we took a close look with probes, we thought Mars had lichens living on it, to explain its color variations or some such; there's no reason to think we have any more clue about M-dwarf planets than we had about mars then, for we have yet so study any.

Good thing one just happens to be in our backyard :D Though realistically, perhaps it turns out easier to study more distant M-dwarf planets, because this one seems not to transit from our perspective. And I think we could study the spectra and hence atmospheric composition of transiting planets sooner than we can hope for direct imaging of them. Not perfectly sure though.

> We just know so wery little about habitability of M-dwarfs

s/M-dwarfs/planets around any star/

Well we just know so very little about planets around any star, excluding 8 planets circling around one out of ~1,000,000,000,000,000,000,000 stars in the observable universe.

yeah, kinda true -- though there's a great deal of extra uncertainty about M-dwarfs in particular in comparison to more sun-like stars, just because we did have this one example to study of that.

But on the other hand, we see all kinds of planet types around all kinds of different stars that pose similar problems (say superearth habitability), so even that only applies to questions about planets more similar so some of the types we can find in our own solar system.

Why would a tidal lock imply no internal dynamo?

well, you need rotation to create a dynamo, and these rotate rather slowly; once per orbit only. Now, it does seem this is still quite fast enough to produce a dynamo, but still the issue is whether it can still be strong enough to create a sufficient magnetosphere to save the atmosphere from completely eroding away, given both how close and how active Proxima Cent. is . Here's a paper that tries to see how much atmosphere planets in habitable zones around red dwarfs could lose given the activity of the star and the magnetosphere they could produce: - http://arxiv.org/abs/1204.0275 . I guess its quite possible various other models have different takes on it, but anyhow that's the worry. I hope we'll see such modelling work done for Proxima Cent. b soon.

The weather is likely rough on the surface, but there could be plenty of good conditions for life under ground/water.

There are other tidal locking modes than 1:1, like mercury has a 3:2 lock. Is that a possibility here?

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