The other day I heard someone say that all energy on earth ultimately comes from the sun, but I don’t know if that is true. Considering deep sea life that derives its energy from ocean vents, would it be possible for life to develop on a rogue planet that is not part of a solar system? Is a star necessary for tectonic activity? If we stopped revolving around the sun would techtonic and geothermal activity cease?
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>The other day I heard someone say that all energy on earth ultimately comes from the sun, but I don’t know if that is true.
So this is pretty close to true if we’re talking about things happening on the surface of the Earth, and especially in the context of something like the Earth’s average air temperature, etc., as radiated heat from Earth’s interior is a very small component of the total surface energy budget. In turn, heating of the surface by incoming solar radiation is effectively inconsequential to the internal heat budget, which instead is dominated by somewhere near equal splits between heat left over from formation and heat generated by radioactive decay, primarily in the mantle and crust. I.e., while in detail the surface energy budget and internal heat budget do contribute to each other, their respective contributions to the other are small enough that we can often just ignore the other when considering one. Now, as we get deeper into the details, things get a bit more messy since both of them set boundary conditions for the other (e.g., the surface energy budget sets the surface temperature of the planet which in turn play a role in the internal energy budget in the sense of influencing the way/rate that heat is loss from the interior via the surface), so we can’t always treat them in isolation from each other.
>Considering deep sea life that derives its energy from ocean vents, would it be possible for life to develop on a rogue planet that is not part of a solar system? Is a star necessary for tectonic activity?
I’ve never seen a specific suggestion that a star is necessary for tectonic activity. The trick is that what we do think is necessary for Earth style “moblie-lid” plate tectonics is a pretty large amount of water (among other conditions). This has come up a variety of times here on AskScience, sometimes in the context of whether life requires plate tectonics or whether liquid oceans are required for plate tectonics. If you look at the first thread, you’ll see a discussion of why we generally think abundant water is necessary for both life and plate tectonics (and as such, life might not require plate tectonics, but since they share some common requirements, we might expect to find them together) and the second thread is useful as it goes into a bit more of the details as to why we think water is required specifically for allowing plate tectonics to develop. This latter thread also highlights that you don’t necessarily need abundant liquid water all the time, but what you really need is a way to really hydrate the upper mantle and keep it hydrated for plate tectonics to exist and persist.
Now, in the context of the question, what this means is that a rogue rocky planet that started off and remained “dry” would be unlikely to be able to develop or support plate tectonics (or life for that matter). If a rogue rocky planet had a good amount of water, things get more speculative as without surface energy input from a star, the amount of liquid water might still be low, but this depends a lot on the details. For example, we see a variety of moons within our solar system where liquid water is not stable at the surface, but with oceans underneath the ice, e.g. Enceladus and Europa. The persistence of these liquid oceans in part reflects the internal heat of these bodies, but in the context of a truly isolated, rogue planet, these are perhaps not good analogues because a large portion of both of their internal heat budgets come from tidal heating from interactions with their parent planets and other moons (something we’d generally expect a rogue planet to lack).
In the end, we’re left with a lot of speculation, reflecting that (1) the question itself is vague (i.e., the answer would depend a lot on the details of the rogue planet), (2) the specific history of a given planet probably plays a role in whether plate tectonics develops (i.e., it’s not just the raw ingredients, but whether particular events do or do not happen, e.g., O’Neill et al., 2018, Stern, 2018), and (3) our understanding of how plate tectonics on Earth (the only example we have of true mobile-lid plate tectonics) started in the first place is incomplete and may remain so (e.g., Harrison, 2024).
Considering all of the above, the answer to “could plate tectonics develop on a rocky rogue planet” is “maybe?”. Probably the best chance would be a planet of the right size and composition to develop plate tectonics that started out around a star in a position conducive to it having a large liquid ocean and getting the right sequence of events to get mobile-lid plate tectonics going (e.g., per many of the references here in the other linked threads, you might need something like a series of impacts to kick-start subduction, or not), having that functioning long enough for the upper mantle to get hydrated, and then it experiencing some sort of gravitational encounter that ejected it from its original solar system. For example, if we imagined something like the Earth of the Proterozoic, where we think mobile-lid plate tectonics was operating (though again, Harrison, 2024 is relevant) and that there was a variety of life in the ocean, was kicked out of its solar system, would plate tectonics and (some) life persist? Plate tectonics, probably, life, harder to say (at least for me as a geologist). Whether plate tectonics could develop on a rogue planet after it had been ejected from its solar system is harder to speculate on but would likely come down to a lot of the specific details.
It’s very speculative, but it seems perfectly plausible that life could develop in oceans under a thick ice layer on such planets, even in the absence of plate tectonics. A few dozen miles of ice form a very good insulator, and heat from radioactive decay in the planet’s rocky core could keep the deep ocean liquid. Such a planet might in fact be far more hospitable to life than the Earth, which is vulnerable to meteorite impacts and long-term orbital instability, and will become uninhabitable in a mere billion years or so as the sun heats up. It would, of course, be ocean-dwelling life in near-complete darkness (though it seems likely that bioluminescence would evolve), and nothing like land-dwelling terrestrial life such as human beings.
If the earth had no heat of its own, if it was simply a lump of hot rock cooling down, it would have been pretty solid in the order of thousands of years. the fact that there is still a non solid mantle and a multi-layer core means its has its own heat source, the radioactivity in its rocks.
Way outside my field of knowledge here, so excuse me if this is silly ask.
Wouldn’t a rogue planet lack any and all surface heat, thus making the surface/crust act as a heatsink, completely turn the interior of the plant cold, and make a rogue planet a giant solid rock/asteroid?
If no: Does the center of a planet just create heat on its own? What’s chemical reaction is used to create that heat?
Short answer, yes.
If the Earth found itself floating in the empty vastness of space with no star nearby, it would be a frozen rock with no activity at all.
An orbital star is necessary. Heat is energy. Energy is required for everything.
Being in the habitual zone (liquid water) is necessary for life to exist (as we know it, and we really don’t know anything).