# What would life near a giant sun be like? **URL:** \ **Category:** Factual Questions\ **Created:** [February 9, 2009, 9:38pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130 "2009-02-09T21:38:45Z")\ **Posts on this page:** 19\ **Page:** 2
**Author:** ![Find\_Friends](https://avatars.discourse-cdn.com/v4/letter/f/c37758/32.png) [@Find\_Friends](https://boards.straightdope.com/u/Find_Friends)\ **Post date:** [February 14, 2009, 8:14pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/21 "2009-02-14T20:14:30Z")
> [@Chronos](#): > > Extending that a bit, the tidal force is proportional to the cube of the apparent size times the density. For instance, from Earth, the Moon and Sun both have the same apparent size, so their tidal forces on Earth are proportional to their densities. The Moon is about twice as dense as the Sun, so it has twice the tidal force. > > You might also be interested to note that surface orbital period (around a spherical body) depends only on density, being proportional to 1/sqrt(density). So it takes about an hour and a half to go around Earth (a basically rocky object), and it also takes about an hour and a half to go around any other basically rocky object like Mercury, Mars, or Ceres. Why, yes, it did once occur to me that the moon’s roughly 2x Sol density would tie in with its roughly 2x Sol tidal force, given that they have about the same apparent size or angular diameter. This was probably about the same time that I realized your second point, something I left off in my post unthread. (This was fewer than ten years ago, and I can still remember a friend rolling her eyes at me for thinking she would care or even, probably, fully understand the matter.) Yes, roughly equally dense objects would have that essential equality in orbital periods of surface satellites. And when there is a substantial difference we can take the square root and then invert it get the orbital period proportionality. Again, for the surface satellite idealization. For instance, Uranus and Jupiter each have roughly a fourth of Earth density. The square root of one fourth is one half, and inverting that we get 2x. So one would expect each period to be twice as long as just under half an hour. For that matter, the density of Sol is in the same ballpark as these two, so again about twice as long as for our low-orbit satellites. Great minds think alike, BTW. 🙂 * * * Now I’m wondering whether I should start a thread detailing the line of reasoning I went through with all the proportionalities, the advantages of looking at things this way, and the problems that go with some of them. No doubt MPSIMS would be the place, since I could hardly start a new GQ thread with a set of answers. - “Jack” ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 14, 2009, 8:21pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/22 "2009-02-14T20:21:53Z")
> [@](#): > > Great minds think alike, BTW. I first noticed the orbital period one while reading a Heinlein book, where he mentions an 84-minute orbit around Phobos. I noticed that that was very similar to Earth’s, so I backed out the reason why. But yes, I do think such a thread would be interesting, and I have a few other formulae and other tidbits I could contribute to it. Put a link here if you do start it. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [February 14, 2009, 8:41pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/23 "2009-02-14T20:41:49Z")
A minor nitpick: > [@True Blue Jack](#): > > …red dwarves have much higher densities than Sol … Just to doublecheck a possibly erroneous assumption here… _White_ dwarves --stars operating on the basis of degeneracy pressure – have densities orders of magnitude greater than Sol. Red dwarves – K and M class Main Seuence stars – would be smaller and cooler than Sol, and therefore have slightly less internal pressure, resulting in them being slightly denser than Sol, just as an A class Main Sequence star would be marginally less dense. But I think in your quick analysis above, you, essaying to contrast red giants and red dwarves, accidentally spoke of the density of white dwarves. Correct? ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [February 14, 2009, 9:24pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/24 "2009-02-14T21:24:44Z")
> [@Chronos](#): > > \<…\>and two different kinds of black dwarfs, which were once main sequence but have evolved far off of it. What would those be? A “black dwarf” IIRC would be a very cooled off white dwarf, which I seem to recall reading that no star in the universe would be old enough to have reached that stage yet. What’s the other kind? (And what would you call a cooled off white dwarf that is now yellow or red in surface color?) ---
**Author:** ![The\_Tao\_s\_Revenge](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)\ **Post date:** [February 14, 2009, 9:58pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/25 "2009-02-14T21:58:08Z")
> [@Walker\_in\_Eternity](#): > > I seem to recall that it is possible to have a habitable planet orbiting a red giant (an old star), but in order to be in the habitable zone the planet would be tidally locked i.e. having one face to the sun at all times, so it would be hot on one side and cold on the other. Wouldn’t all the water freeze on the night side or would the atmosphere, oceans, etc be able to shift the heat around to keep the dark side above freezing? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 14, 2009, 10:10pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/26 "2009-02-14T22:10:22Z")
> [@](#): > > What would those be? A “black dwarf” IIRC would be a very cooled off white dwarf, which I seem to recall reading that no star in the universe would be old enough to have reached that stage yet. What’s the other kind? One type is a cooled-off white dwarf, and the Universe probably is old enough to have a few of those knocking about (though it depends on just cool it has to be before you’ll call it “black”). The other type is a dead, cooled-off _red_ dwarf, and it’ll be a long while yet before we get any of those, since red dwarfs are very frugal in their fuel consumption and last practically forever. When I said “there are two kinds of black dwarfs”, I meant that there are two such kinds of objects that can exist, not that there actually are any in the Universe. ---
**Author:** ![The\_Tao\_s\_Revenge](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)\ **Post date:** [February 14, 2009, 10:13pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/27 "2009-02-14T22:13:08Z")
> [@Chronos](#): > > One type is a cooled-off white dwarf, and the Universe probably is old enough to have a few of those knocking about (though it depends on just cool it has to be before you’ll call it “black”). The other type is a dead, cooled-off _red_ dwarf, and it’ll be a long while yet before we get any of those, since red dwarfs are very frugal in their fuel consumption and last practically forever. When I said “there are two kinds of black dwarfs”, I meant that there are two such kinds of objects that can exist, not that there actually are any in the Universe. This might sound like a silly question but what color is degenerate matter (what I think they call the stuff that makes a white dwarf)? What color would a black dwarf from a white dwarf be if you shined a flash light on it? ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [February 15, 2009, 12:23am UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/28 "2009-02-15T00:23:34Z")
> [@The\_Tao\_s\_Revenge](#): > > Wouldn’t all the water freeze on the night side or would the atmosphere, oceans, etc be able to shift the heat around to keep the dark side above freezing? Venus has a very slow rotation period, which I forget at the moment. Slow enough that it might as well not be rotating ( at least in comparision to Earth and Mars). The super thick atmosphere moves the heat around enough to even out the temp very effectively. ---
**Author:** ![The\_Tao\_s\_Revenge](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)\ **Post date:** [February 15, 2009, 4:22am UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/29 "2009-02-15T04:22:40Z")
> [@billfish678](#): > > Venus has a very slow rotation period, which I forget at the moment. Slow enough that it might as well not be rotating ( at least in comparision to Earth and Mars). > > The super thick atmosphere moves the heat around enough to even out the temp very effectively. That’s true but Venus has a very thick blanket, and thinking about it if the heat was getting distributed around the whole planet wouldn’t it be the same as the planet rotating? I mean same amount of heat distributed over the same amount of area. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [February 15, 2009, 12:48pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/30 "2009-02-15T12:48:52Z")
Kal-El would have no superpowers , living on a planet around a red sun. Only under a yellow sun, does he become superman. ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [February 15, 2009, 2:35pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/31 "2009-02-15T14:35:35Z")
> [@MeDrewNotYou](#): > > Bolding mine > Assuming that a terrestrial planet could form around one of those stars, would there even be enough time for the materials to coalesce, much less form a place cool enough for life? I’m sure I’ve read a couple of stories which posit a nice normal rocky planet around a nice old normal sun which is graviationally captured by a giant, with some ensuing orbital jigggery-pokery that results in a nice sky-filling giant sun and intelligent life to admire it, rather than a cloud of debris or a cinder. Is this physically possible, or is it just handwaving with enough tinsel round it to fool those as ignorant as I am? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 15, 2009, 10:00pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/32 "2009-02-15T22:00:16Z")
> [@](#): > > This might sound like a silly question but what color is degenerate matter (what I think they call the stuff that makes a white dwarf)? What color would a black dwarf from a white dwarf be if you shined a flash light on it? Probably a pretty good black. Heck, almost all stars are already approximated as being black, anyway. > [@](#): > > I’m sure I’ve read a couple of stories which posit a nice normal rocky planet around a nice old normal sun which is graviationally captured by a giant, with some ensuing orbital jigggery-pokery that results in a nice sky-filling giant sun and intelligent life to admire it, rather than a cloud of debris or a cinder. > > Is this physically possible, or is it just handwaving with enough tinsel round it to fool those as ignorant as I am? Possible? Sure. Not very likely, but then, I think that most such stories probably acknowledge that (Niven’s _The Integral Trees_ and sequel _The Smoke Ring_ certainly do, though that’s a slightly different situation). ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [February 16, 2009, 8:01pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/33 "2009-02-16T20:01:34Z")
> [@Chronos](#): > > Possible? Sure. Not very likely I think that’s pretty much a given even for the better class of science fiction 🙂 ---
**Author:** ![Find\_Friends](https://avatars.discourse-cdn.com/v4/letter/f/c37758/32.png) [@Find\_Friends](https://boards.straightdope.com/u/Find_Friends)\ **Post date:** [February 24, 2009, 8:37pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/34 "2009-02-24T20:37:57Z")
> [@Polycarp](#): > > A minor nitpick: > > Just to doublecheck a possibly erroneous assumption here… _White_ dwarves --stars operating on the basis of degeneracy pressure – have densities orders of magnitude greater than Sol. Red dwarves – K and M class Main Seuence stars – would be smaller and cooler than Sol, and therefore have slightly less internal pressure, resulting in them being slightly denser than Sol, just as an A class Main Sequence star would be marginally less dense. But I think in your quick analysis above, you, essaying to contrast red giants and red dwarves, accidentally spoke of the density of white dwarves. Correct? First, sorry to take so long to notice and respond. I really did mean red dwarf stars. Of course, “much higher” may have been unclear, especially in the context of the much (“extremely”) lower densities of the red giants, even the smallest of them. And, of course, there is no comparison with white dwarf stars for extreme density. So I may have overstated the matter with my choice of words. As said upthread, a combination of factors leads to the conclusion that a planet with sufficient insolation by a red dwarf would have to also be subject to tidal force lock, which would definitely be a problem for originating life. If I ever start a thread about proportionalities, I’ll be sure to cover it. (And, yes to Chronos, I will link to it here.) BTW, the threads here are oriented to life origination. Maybe this is the most direct interpretation of the OP, but it seems to me that a discussion of colonization and survival has been skipped over. ETA: Oops! Except for something in one of your posts! :smack: - “Jack” ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [February 24, 2009, 8:43pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/35 "2009-02-24T20:43:00Z")
> [@Chronos](#): > > The biggest difficulty is that large stars live fast, die young, and leave a beautiful corpse. Whereas our Sun has lived for about 5 billion years, and is expected to have about that much more, very large stars can live for as short as a million years or less. Life does seem to have formed very quickly on our world, but we’re still talking hundreds of millions of years when we say “quickly”. So it seems likely that life would never have a chance to appear in the first place around a giant star. but is it possible that the much greater energy output from a large star could speed up the process for the formation of life? it took the amount of time here on Earth that it did, because ultimately the formation of life was based on the amount of energy from the Sun. If you greatly increase that input, couldn’t it speed up the formation of life and evolution of life-forms? (Just wild speculation on my part, as IANAScientist.) ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [February 24, 2009, 8:58pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/36 "2009-02-24T20:58:25Z")
> [@Lumpy](#): > > A hot star like Sirius or Rigel would look like a tiny, blindingly bright welder’s flame- in fact one problem would be how sighted animals could avoid burning out their retinas by an accidental glance at such a light source. Perhaps a perpetually clouded planet would be a necessity. temperature, the star would have a larger angular diameter as seen from the planet. You would see a red orb dim enough to look at comfortably taking up a much larger portion of the sky. Doc Smith already solved that problem: the inhabitants of Rigel IV don’t have sight, but the sense of perception, a sort of telpathic sight that does not depend on lightwaves. You don’t have to be a scientist to solve all these issues. 🙂 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 24, 2009, 9:05pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/37 "2009-02-24T21:05:49Z")
> [@](#): > > but is it possible that the much greater energy output from a large star could speed up the process for the formation of life? Damnit, Jim, I’m a physicist, not a doctor! In other words, is there a biologist in the house, specifically one specializing in abiogenesis? It looks like a good question to me, but I have no idea as to the answer. ---
**Author:** ![Laudenum](https://avatars.discourse-cdn.com/v4/letter/l/7993a0/32.png) [@Laudenum](https://boards.straightdope.com/u/Laudenum)\ **Post date:** [March 29, 2009, 9:03pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/38 "2009-03-29T21:03:36Z")
> [@Laudenum](#): > > I assume that by now you have all seen that diagram that shows the relative size of the Earth to the the Sun, the Sun to another, bigger star, until you get to this giant star 20,000c bigger then the sun. :oDoes anyone have a link to this diagram? I forgot where to find it. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 29, 2009, 9:43pm UTC](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130/39 "2009-03-29T21:43:54Z")
> [@Laudenum](#): > > :oDoes anyone have a link to this diagram? I forgot where to find it. Not quite what you meant, but [this video](http://www.youtube.com/watch?v=I34FNr_peUk&feature=related) does a great job of it. [Previous page](https://boards.straightdope.com/t/what-would-life-near-a-giant-sun-be-like/485130.md?page=1)