In 1999, David Stevenson wrote a short correspondance to Nature, suggesting that radiogenic heating of free floating planets with thick atmospheres might lead to them having surface temperatures high enough for liquid water
These would be planets which had been ejected from the stellar system in which they formed, and could retain thick, possibly hydrogen rich atmospheres, since there would be no sunlight to drive hydrogen escape.
Natural heating from radioactive elements would provide sufficient heat flux through the surface that with deep enough an atmosphere the temperatures at the surface could sustain liquid water for hundreds of millions, or billions, of years.
Now some crazy guys have come up with an extension of this scenario; that in some fraction of cases binary planets (like the Earth-Moon or Pluto-Charon systems) could be ejected bound (but possibly with mildly eccentric orbits), and the tidal heating would provide significant additional heat flux for some hundreds of millions of years, possibly expediting the onset of life on the surface, since there might be an order of magnitude free energy flux.
Good article summarising this here
Fun thing is that microlensing surveys planned for the moderate term near future may see free floating planets, and binary planets have a pretty clean observational signature in microlensing observations.
The nearest such system may be as close as a few parsecs away (say ~ 10 light years) and could be detected directly in principle, as a very red, faint, high proper motion source. To characterise it, a ~ 1 km space based infra-red telescope would be useful, so maybe for the 2030s...
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Was this idea ever used in Science Fiction?
"Orphan planets" such as Steinn describes were mentioned a few times in this book. They weren't a major plot point or anything though - Ian Stewart being the prolific popularizer that he is, I guess he and his co-author were just trying to cram as many interesting ideas as possible into their story.
I haven't read Watson's "Heaven", read some of his earlier stuff.
Free floating planets have certainly been considered before, both in the scientific and science fictional literature.
I'm pretty sure that all the instances I know of had them as airless, frozen balls.
I wanna say one of the Haldeman books includes an example of a free floating planet being used as a "very safe" base for warfare, and I think there may be some other instances.
To my knowledge free floating planets with liquid water were not considered before Stevenson's article, and the possibility of ejecting bound binary planets is novel as far as I know.
We actually sent it originally as a followup correspondance to Nature a long time ago, but the editor didn't want to do "seconds" - the original Stevenson idea was neat, but the follow through wasn't new enough.
So, as these things go, we made it meatier and sent it to ApJLetters, eventually.
Got distracted by some Hubble data for a while.
Vernor Vinge used the idea in "The Science Fair."
You had me worried for a second there...
I found my copy of "Collected Stories..." [not one of Vinge's best, btw, not even close to "Run Bookworm, run!" or "True Names...]
Anyway, the scenario in "Science Fair" is a rogue star, with a hint at the end that it is a stellar object with a habitable planet around it.
Now the author notes discuss free floating planets, but the story doesn't really, it is definitely a high proper motion star from the description.
The legendary "Pail of Air" by Leiber, of course, discusses the Earth becoming a free floater, but the scenario of life forming first in orbit around a star and persisting after ejection is distinct from life forming directly on a free floater.
I am bummed about "Science Fair", I know I read it, though it was not memorable, and it scoops a nifty idea I talked to David Taylor at Northwestern about...
Ah well, I may still blog it.
While it is easy to see how such a planet could be warm at first (like us), how would it mantain a constant surface temperature over a billion year timescale? Both tidal and radiometric heating decrease rapidly with time, and condensing H2O should provide a strong negative feedback, so shouldn't such a planet go from steam to ice fairly quickly?
We don't claim it will keep a constant surface temperature over time--any planet would have to cool down as the tidal forces slacken (a few hundred million years). But we make our calculations relative to the _current_ radiogenic heating of the earth, so radiogenic heating would still be important for Gyr, provided the planet had a thick enough atmosphere. It might start off like Hawaii, but it would probably end up like Hoth with some hot springs. Now it's up to the evolutionary biologists to give us a handy scaling law on how quickly life evolves and adapts to changing environments...
Does the planet (as opposed to the moon) ever end up in orbit around the Jovian in these simulations?
weird website