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A scientific fact/tidbit you recently learned that you thought was interesting

About 3/4 of all stars in the universe are red dwarfs, and they are unlikely to support life.
 
bigred said:
About 3/4 of all stars in the universe are red dwarfs, and they are unlikely to support life.
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Why the latter?

Red dwarf stars last much longer than stars like our sun, so the window of opportunity for life to begin and evolve in such systems would be immense. Earth was already about two thirds of the way through its window when complex life evolved here.
 
The low light & temperature means that, for a planet to be warm enough for liquid water, it would need to be so close to the star that it would be highly exposed to any solar/stellar wind it produces and any flares, ejections, & other changes in the star's output (which I think I recall those stars have more frequently anyway). Also, the planet at such a short distance would probably be tide-locked, which means having a permanently roasted side and a permanently frozen side, with horrific winds in the ring where they meet, if there somehow is an atmosphere.
 
Proximity to a star is not essential for liquid water. There are oceans of water under the surface of several of the moons of Jupiter and Saturn, where life might well exist.
 
Well, more accurately what's needed is a source of energy, otherwise the whole planet will reach equilibrium with the temperature of the CMB, which is to say, less than 3 Kelvin. That's not just enough to freeze water, but even hydrogen. (Hydrogen freezing points is about 14 Kelvin.)

Of course tidal energy from a big planet or internal processes or whatever, still counts, which is what's happening with those moons.
 
Well, what I learned recently: Hi, my name is Hans and I'm stupid. A stupid audiophile, to be exact. Turns out that getting a sound card that does 32 bits sampling at 384 kHz makes no difference whatsoever:

 
HansMustermann said:
Well, more accurately what's needed is a source of energy, otherwise the whole planet will reach equilibrium with the temperature of the CMB, which is to say, less than 3 Kelvin. That's not just enough to freeze water, but even hydrogen. (Hydrogen freezing points is about 14 Kelvin.)

Of course tidal energy from a big planet or internal processes or whatever, still counts, which is what's happening with those moons.
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The main source of heat of planet Earth is radioactive decay, isn't it? A rocky planet of the right size, somewhat larger than our planet I'd think, would have the right surface-to-mass ratio, given a concentration of radio-isotopes, that heat from decay would be in equilibrium with net heat radiation away from the surface, such that temperatures conductive to maintaining life are present near enough to the surface.
 
Actually, no, not really. Earth receives 44 quadrillion (4.4 x 1016 W) watts of energy (well, ok, POWER) from the Sun. Earth's core is estimated to produce about 44 terawatts (4.4. x 1013 W). That's 0.1% of the energy that comes from the Sun, or about the same percentage of the total energy.

Going Stefan–Boltzmann on its ass, we're talking about a difference of (T1/T2)4=1001, then T1/T2=5.6 (slightly rounded down.) But that's in Kelvin, so T1 (current temp) is an average 288 Kelvin, while T2 (without the sun) would be about 288/5.6=about 51.4K. (Again, rounded to one decimal, because we're just doing back of the napkin taking-the-piss.)

That's not just low enough to freeze water, it's low enough to freeze the nitrogen (freezing point: 77 K) in the atmosphere and juust barely enought to freeze the oxygen too (freezing point: 54.4 K). Well, ok, maybe not entirely the latter, since that's at 1 atm, which would no longer be the case. A very thin atmosphere would be left above the ice, but with most of the nitrogen missing, and the Earth's magnetic field stopping (no ocean => no plate tectonics => not much rotation of the core) most of it would be blown away by the solar winds.


So not on the surface, no.

On the other hand, in the depth of the ocean near the volcanic vents, there would be pockets of liquid water that could support bacterial life.
 
HansMustermann said:
That's not just low enough to freeze water, it's low enough to freeze the nitrogen (freezing point: 77 K) in the atmosphere and juust barely enought to freeze the oxygen too (freezing point: 54.4 K).
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Just to quibble, nitrogen freezes at 63K, 77K only liquefies it. Still cold enough to freeze it though.

Dave
 
HansMustermann said:
Well, more accurately what's needed is a source of energy, otherwise the whole planet will reach equilibrium with the temperature of the CMB, which is to say, less than 3 Kelvin. That's not just enough to freeze water, but even hydrogen. (Hydrogen freezing points is about 14 Kelvin.)

Of course tidal energy from a big planet or internal processes or whatever, still counts, which is what's happening with those moons.
Click to expand...

And which could also be happening on moons in the planetary systems of red dwarfs, so such systems could support life. If we rule them out because there would be no planets in the Goldilocks zone, as was suggested, we might be significantly underestimating the number of possible abodes of life in the universe.
 
HansMustermann said:
Actually, no, not really. Earth receives 44 quadrillion (4.4 x 1016 W) watts of energy (well, ok, POWER) from the Sun. Earth's core is estimated to produce about 44 terawatts (4.4. x 1013 W). That's 0.1% of the energy that comes from the Sun, or about the same percentage of the total energy.

Going Stefan–Boltzmann on its ass, we're talking about a difference of (T1/T2)4=1001, then T1/T2=5.6 (slightly rounded down.) But that's in Kelvin, so T1 (current temp) is an average 288 Kelvin, while T2 (without the sun) would be about 288/5.6=about 51.4K. (Again, rounded to one decimal, because we're just doing back of the napkin taking-the-piss.)

That's not just low enough to freeze water, it's low enough to freeze the nitrogen (freezing point: 77 K) in the atmosphere and juust barely enought to freeze the oxygen too (freezing point: 54.4 K). Well, ok, maybe not entirely the latter, since that's at 1 atm, which would no longer be the case. A very thin atmosphere would be left above the ice, but with most of the nitrogen missing, and the Earth's magnetic field stopping (no ocean => no plate tectonics => not much rotation of the core) most of it would be blown away by the solar winds.


So not on the surface, no.

On the other hand, in the depth of the ocean near the volcanic vents, there would be pockets of liquid water that could support bacterial life.
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How do you get from no plate tectonics => not much rotation of the core?
 
rjh01 said:
It would be very small life forms. Probably like what exists in our ocean vents.
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I don't see why. Some of those oceans are immense, and unless I'm missing something (which is entirely possible) I would think the conditions that are suitable for life would prevail across fairly large regions of them.
 
Pixel42 said:
And which could also be happening on moons in the planetary systems of red dwarfs, so such systems could support life. If we rule them out because there would be no planets in the Goldilocks zone, as was suggested, we might be significantly underestimating the number of possible abodes of life in the universe.
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Oh, in the case of red dwarfs, it's not just the Goldilocks effect. Those stars are magnetically unstable and periodically blow up. Any star that's close enough to either be in that zone, or even worse, tidal locked enough to be heated by the same effect as Jupiter's moons (which actually means even closer), would get its atmosphere blown clean off and surface scorched before it even got to evolve life.

That's a fairly recent tidbit that took everyone by surprise as they watched Alpha Centauri do just that. Previously it was thought that red dwarfs were THE ideal plants to survive around in the future, since they'll last for hundreds of billions of years, long after all other suns have up and died. Turns out that, yeah, no, they have massive periodic explosions that make their planets utterly bare pieces of rock.
 
sphenisc said:
How do you get from no plate tectonics => not much rotation of the core?
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Because it's the accepted theory for why Venus ended up without a magnetic field and most hydrogen or any oxygen not bound to carbon atoms blown away?

Not that it would matter all that much either way, once most of your atmosphere is frozen solid anyway. Like even if you still had a magnetic field, having a few millibars of atmosphere left, and layers of frozen gasses like on Pluto below, would not exactly support life. Is all I'm saying.
 
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HansMustermann said:
Oh, in the case of red dwarfs, it's not just the Goldilocks effect. Those stars are magnetically unstable and periodically blow up. Any star that's close enough to either be in that zone, or even worse, tidal locked enough to be heated by the same effect as Jupiter's moons (which actually means even closer), would get its atmosphere blown clean off and surface scorched before it even got to evolve life.

That's a fairly recent tidbit that took everyone by surprise as they watched Alpha Centauri do just that. Previously it was thought that red dwarfs were THE ideal plants to survive around in the future, since they'll last for hundreds of billions of years, long after all other suns have up and died. Turns out that, yeah, no, they have massive periodic explosions that make their planets utterly bare pieces of rock.
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That particular tidbit is new to me.

Would moons like the ones in our solar system that might potentially have life, i.e. that circle gas giants a long way out from the star, be as badly affected?
 
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