What's the absolute closest two Earth-like planets could orbit each other ala. Pluto and Charon, and still support life and an atmosphere?
What's the absolute closest two Earth-like planets could orbit each other ala. Pluto and Charon...
Juan Nguyen
Joshua Martinez
why would they not support an athmosphere and life?
Angel Lewis
Roche limit.
Hunter Long
Distance from their parent star is far more important.
Two closely orbiting objects of similar size would tidally lock very quickly and stop pumping tidal energy into one another. Europa for example is squeezed by Jupiter's gravity only because the other big moons of Jupiter keep tugging it out of its orbit very slightly, which acts like a stress ball being squeezed.
Two tidally locked Earth sized objects would act like two stress balls that were squeezed then held squeezed, meaning although they remain deformed they aren't actually being warmed up by the interaction anymore.
Therefore if tides are a significant cause of geologic instability, Earth would be less stable than two tidally locked worlds.
As long as they didn't get close enough to tear each other apart and they were within the habitable zone of their star there's no reason they wouldn't form atmospheres and eventually life, providing the right resources are available.
Brody Garcia
and are absolutely right.
However, the Roche limit applies when the bodies have equal densities. It would be possible to have two close worlds whose rock and soil were perfectly stable but whose atmospheres (and possibly oceans) overflowed their Roche lobes and connected them. You could fly an airplane from one to the other.
The physicist Dr Robert Forward wrote several novels based on this idea and laid out the physics, in detail, as Afterwords in those books.
Jacob Sanders
>The physicist Dr Robert Forward wrote several novels based on this idea and laid out the physics, in detail, as Afterwords in those books.
Basically same thing with this novel
en.wikipedia.org
Jordan Kelly
Tidal locking would probably mean less "kneading" of the crust and thus limit the geological carbon cycle. That is one of the problems with Mars. So a tidally locked Earth would be stable dead.
William Hill
If the two planets orbiting each other orbited a star wouldn't their respective crusts still be "kneaded" by the gravitational influence of the star since the planets would essentially rotate around their mutual barycenter with respect to their parent star as they orbit around it?
Parker Sanders
What about rocheworlds?
Luke Flores
Good question. It would have to be so close to the star that there is a noticeable gravity gradient. At that point In am not sure the two planets would be tidally locked.
You could of course cheat and place the smaller planet in the L5 of the larger planet, both co-orbiting the sun.
Isaiah Foster
So it would have to be a red dwarf star that they rotate around probably, and since red dwarf stars are much less magnetically stable and more likely to blast planets close to them with powerful CMEs the possibility of life would still be low.
Ethan Brooks
sounds pretty cool. Is it a good story, or just a neat setting?
Justin Sullivan
When the news on the Trappist system was hot it was mentioned that red dwarves can be stable. In any case life in an ocean will be far more protected than on land.
Kevin Bell
True, but unless the planets had very strong magnetospheres the solar wind would blast away their atmospheres and hence most of their water save the water that's frozen in the poles much like Mars.
James Watson
That seems to be at odds with the idea that red dwarves should be hospitable to ancient civilisations.
Blue giants are also rather aggressive. Does this mean that only yellow sun-like stars are comfy?
Christopher Price
Well, Forward wasn't the greatest at character development. Don't expect Faulkner or Hemmingway.
But it's interesting, well worked out, and we meet some cool aliens. Really "alien" aliens who couldn't possibly be played by guys in rubber suits.
It was reprinted a couple of times. The copy I have here is entitled "Rocheworld" and says "At last the complete story." 155,000 words. Baen. 1990.
Forward also wrote novels about life on a neutron star. The Cheela are degenerate matter. Their "day" is only a fraction of a second. Nuclear reactions are so much faster than chemical ones that the Cheela are primitives when humans contact them and four days later they're teaching _us_! Wars have been fought, empires risen and fallen.
Gabriel Russell
It's not that blue giants are aggressive.
They just don't last long enough.
To be warm enough for liquid water the planet of a red dwarf would have to be close in and likely tide-locked. But you could still have a habitable moon of a super-Jovian. It might be tide-locked to the planet but would still get sunlight on all sides within the time it took to orbit its primary.
Evan Gray
Would the moon be protected enough by the super-Jovian planet's magnetopause?
Also, wouldn't the super-Jovian planet attract a lot of asteriods/comets that could potentially endanger its moon?
Brandon Gutierrez
Both good questions.
Extrasolar systems are so bizarre and varied I'd hesitate to hazard definitive answers.
The super-Jovian _might_ have "cleaned out" most of the debris in its system if it migrated inwards. So there might not be a lot of leftover trash.
For anyone interested in all the myriad possibilities I recommend bloomsbury.com
I have the hardcover. Recent, authoritative, and the best I've read on the subject.
Isaac Collins
The part always facing the super-Jovian would probably receive less sunlight since the sun would never directly face that part from zenith. Weather would be interesting.
Leo Powell
Not direct sunlight -- if it was close-in.
By the same token though, a large chunk of the sky might be filled by the primary and lit with reflected sunlight.
Ever read Niven's "known space" stories?
news.larryniven.net