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.
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.
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?
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?)
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?
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?
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.
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?
Probably a pretty good black. Heck, almost all stars are already approximated as being black, anyway.
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).
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:
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.)
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.
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.
