On July 21 at 10 am, Seti Talks will be discussing the topic of "Could Rogue Planets Harbor Life". Supposedly there are 50 billion such planets in the Milky Way. I would think that the answer was obvious: no. So what is there to discuss?
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8$\begingroup$ I wouldn't rule out life anywhere in the universe. $\endgroup$– PeterHCommented Jul 15, 2021 at 14:22
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2$\begingroup$ Life doesn't have to take a form in any way similar to what we've previously been exposed to in this world. When we look at things like the need for water, carbon-based chemistry, etc., these types of natural characteristics are simply based on past experience, not proven laws of the universe. $\endgroup$– PanzercrisisCommented Jul 15, 2021 at 20:05
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26$\begingroup$ Somewhere on a rogue planet - "Could star-bound planets harbor life? Seems unlikely, all that radiation." $\endgroup$– Don BransonCommented Jul 15, 2021 at 20:51
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3$\begingroup$ Life, uh, finds a way. $\endgroup$– AnoECommented Jul 16, 2021 at 9:07
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$\begingroup$ @Panzercrisis: It's hard to imagine any form of life that doesn't require an external energy source though. $\endgroup$– Mooing DuckCommented Jul 16, 2021 at 23:05
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3 Answers
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There's also the possibility that a rogue giant planet may have a moon with a subsurface ocean of liquid water due to tidal heating in an orbit close enough to its parent planet. E.g. if Jupiter was a rogue planet its moon Europa could still harbor life because of tidal heating.
Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection. A large satellite would be a source of significant geological tidal heating26.
26. Debes, John H.; Steinn Sigurðsson (20 October 2007). "The Survival Rate of Ejected Terrestrial Planets with Moons". The Astrophysical Journal Letters. 668 (2): L167–L170. arXiv:0709.0945
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2$\begingroup$ @Pureferret Why would you think rogue planets can't have satellites? $\endgroup$– JohnCommented Jul 15, 2021 at 16:25
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$\begingroup$ I thought if a planet was knocked out of orbit, that the moon would be almost certainly knocked away? Is that wrong? $\endgroup$ Commented Jul 15, 2021 at 18:26
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$\begingroup$ @Pureferret From Wikipedia "Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection. A large satellite would be a source of significant geological tidal heating.[26]" $\endgroup$– AubrealCommented Jul 15, 2021 at 18:36
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2$\begingroup$ A rogue planet could also pick up moons after being ejected. $\endgroup$ Commented Jul 15, 2021 at 20:57
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1$\begingroup$ @Pureferret An ejected planet can retain its moon, see my answer here: astronomy.stackexchange.com/questions/41832/… $\endgroup$– Connor Garcia ♦Commented Jul 15, 2021 at 22:20
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In short, if a rogue planet has enough internal heat and retains enough of that internal heat by a thick atmosphere or within a miles-deep ice crust, it could be warm enough for liquid water and thus possibly for Earth-like lifeforms.
here is a link to an article on the subject:
https://futurism.com/life-could-exist-on-rogue-planets-that-dont-have-stars
And an advanced civlization capable of building artifical habitats on lifeless worlds or in outer space could settle a rogue planet, providing their own energy source from nuclear fusion.
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2$\begingroup$ I think you need to trim the end of the link: futurism.com/… . Perhaps of interest to the OP, the popular science youtube channel Kurzgesagt had some videos on this topic: youtube.com/watch?v=gLZJlf5rHVs , youtube.com/watch?v=M7CkdB5z9PY $\endgroup$– epsCommented Jul 14, 2021 at 18:30
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The discussion will focus on
the term rogue planet is an oxymoron, as it's missing the principle defining feature of a planet.
a Jupiter-sized body without a sun will be warmer than you would have thought. And they could be even larger, up to being brown dwarfs.
moons of such a body can be heated by tidal forces, without regard to whether there's a sun or not.
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$\begingroup$ I would agree that rogue planet is a bad term. In my opinion, "rōnin planet" would be more adequate. en.wikipedia.org/wiki/R%C5%8Dnin $\endgroup$ Commented Jan 27, 2023 at 5:43