A recent question asked for a natural mechanism for a creature to escape one planet and go to another. The answers prompted me to this question.

Given any answer to this, is there any plausible case for evolution to enable a creature to leave a planets biosphere and go to another, not by begin blasted from the surface by a meteorite or titanic volcanic explosion, or genetic engineering. I suppose in other words; is naturally evolved panspermia. possible?

My guess is no, but cannot help but think there may be perhaps some cyclic devastating conditions that eventually leads to this possibility. "Life finds a way."

I would prefer the creature be multicellular. But would accept answers for spores or seeds type transmission.

EDIT: To make things even easier, we can assume a minimal gravity to sustain a life bearing atmosphere.

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    $\begingroup$ Hmmm... Part of the problem is that energy (aka "life") tends to find the path of least resistance (the lowest energy state). What would lead to space, rather than a planet's surface, to represent the lowest energy state? Maybe if early life evolved a love for gamma rays... but that would mean some random mutation would find gamma rays at a higher altitude, leading to that mutation being favored. Curious question! $\endgroup$
    – JBH
    Jun 17, 2022 at 7:12
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    $\begingroup$ @JBH Good idea!, maybe not gaman but plausibly UV? I've never came across a realistic hypothetical critter that processed UB but...The creature could start conditioning itself by acclimating to high altitudes to attain better access to UV. " 6 to 10 percent increase in UV exposure for every thousand feet of elevation" is a significant enough draw. Just need to know if there's a way that UV could be sufficiently beneficial to induce the behavior? $\endgroup$
    – Gillgamesh
    Jun 17, 2022 at 11:58
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    $\begingroup$ @Gillgamesh There are real-world fungi that perform radiosynthesis ( en.wikipedia.org/wiki/Radiosynthesis_(metabolism) ) using UV and gamma radiation. See also en.wikipedia.org/wiki/Radiotrophic_fungus $\endgroup$ Jun 17, 2022 at 15:13

2 Answers 2


Yes, but not on a planet

First off, it is impossible to me that life evolves naturally to panspermia on a planet. The energy requirements for launching yourself into space are astronomical, the further travel from the edge of space into the rest of the star system even more so. There is simply too much energy that needs to be gathered and stored safely for a long time. Even if a creature can do this, how will it safely ignite the fuel and fly up into space?

Most plausible would be a microorganism that blasts it's offsping in excessively protected cocoons. Some bushes hold their seeds until a forest fire. These eggs could hatch after exposure to extreme heat and cold. The creatures would blow up a large portion of their offspring, but in so many cases there's the 'get many offsping and see what survives' strategy. It still requires too much energy, an implausible explosion or ignition and a protective shell. It seems much more plausible such huge stores of energy would be used for movement, protection or much, much more offspring.

That being said, I can see two playsible ways for panspermia to evolve. One is still being blasted into space at a regular basis that space flight is a great way to survive. The other is to not start on a planet to begin with. If you start at asteroids there are plausible mechanisms for many sizes of creatues to get off them. Then they can fly towards other asteroids, moons or other suitable celestial bodies. It isn't hospitable, but the same can be said of hot deserts or the icecaps in the Arctic circle. You just need to be adapted well enough.

  • $\begingroup$ Asteroids are far too small and irregular in shape to develop a sustainable atmosphere. Moons or dwarf planets might be a feasible origin, but even all of the asteroids in the trojan belt combined would be smaller than our moon. $\endgroup$ Jun 15, 2022 at 18:15
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    $\begingroup$ @TitaniumTurtle Who says you need an atmosphere? Just develop under an ice shell, and move directly into vacuum. $\endgroup$ Jun 15, 2022 at 18:19
  • $\begingroup$ @TitaniumTurtle Logan is correct. The intent is to develop life that is already focusing on living without atmosphere. They are set to hoard important molecules and hold on to them. That makes them more plausible than creatures needing to transit from atmosphere to space and back. The requirements for living in atmosphere are just different than space. $\endgroup$
    – Trioxidane
    Jun 15, 2022 at 18:32
  • $\begingroup$ @LoganR.Kearsley & OP There is no life outside of an atmosphere. Stellar radiation basically burns everything away. It's like sterilization by means of broad spectrum laser. Sure, a pre-existing life form might develop in a way to survive in space, but there is no way life would naturally develop without an atmosphere, at least a thin one. That's one of the biggest reasons Mars only has traces of microbial life hidden under layers of ice and rock. Even with suits we could only stay there sustainably with layers of radiation shielding and Mars actually does have an atmosphere, asteroids don't. $\endgroup$ Jun 15, 2022 at 19:22
  • $\begingroup$ @TitaniumTurtle You just admitted that "a pre-existing life form might develop in a way to survive in space" That's exactly what I proposed, so what exactly is your objection? $\endgroup$ Jun 15, 2022 at 20:17

Assuming a minimal gravity to retain a life-sustaining atmosphere does not make things easier!

Retaining an atmosphere requires a certain minimum escape velocity, and that's exactly what you want to minimize. Life, fortunately, does not require an atmosphere. Life requires liquid, but deep ocean life would get along just fine if there were no atmosphere above it, and plenty of organisms (famously including tardigrades) can survive in stasis in vacuum. Humans can even operate for up to 90 seconds (in the ideal case) in vacuum without permanent injury, so it's not that hard to imagine an organism that has developed in an ocean (or at least, say, a sub-surface lake) and then evolved full resistance to vacuum, maintaining its own internal liquid environment. Really, it's not that much different from Earthling creatures moving from the ocean onto land, and developing impermeable skin to take our watery environment with us.

Liquid environments can exist under icy or rocky shells, with no need for an atmosphere, on bodies with much lower escape velocities. The ideal environment for evolving an organism that naturally propels into space is, therefore, probably something like a small ice moon like Enceladus--which does, in fact, have geysers that expel material above escape velocity--or a large cometary / Kuiper-belt object like Pluto or Arrokoth--large enough to have significant internal heat, and retain liquid underneath an ice shell, but small enough to easily escape from.

Robert Forward describes this kind of organism in Camelot 30K. (Spoilers for a 29-year-old SF novel incoming.) In that novel, intelligent life is discovered on a Kuiper-belt object at 30K. The animal-analogs are endotherms, which actively maintain their own pressurized internal liquid environment against the low-temperature, hard vacuum environment of the world's surface. The ecosystem survives on the energy of reactive chemical radicals left in the ice by the passage of cosmic rays, and the heat released by bioaccumulating radionuclides.

The power input from cosmic rays is not huge, and radionuclides are rare, so they are using up the energetic resources of their tiny world far more quickly than they will be replenished--which means that they cannot survive indefinitely on just one world. They must travel between low-gravity icy bodies. And in fact, it turns out that every organism in the alien "ecosystem" is actually genetically identical--the plants, animals, people, everything, are actually just clones of a single organism, exhibiting extreme phenotypic plasticity (like different casts of ants) in order to instinctively build a structure that will launch their colony into space--which kills most of the individuals, but allows fertile spores to drift to other bodies where they can germinate and start the cycle over again.

  • $\begingroup$ Camelot 30K has been cited here twice in a month on different topics, remarkable! $\endgroup$
    – user86462
    Jun 17, 2022 at 5:39
  • $\begingroup$ +1 for the knowledge. But the connection is a bit to teenious. The creatures already exist in an environment as deadly as space. There's no need for a pressure to encourage them to escape, indeed some are likely to have been ejected from their native environment accidently. $\endgroup$
    – Gillgamesh
    Jun 17, 2022 at 11:57
  • $\begingroup$ @Gillgamesh That's kinda the whole point. The only way you get pressure to adapt to leaving your world and travelling through space... is if you develop in an environment where you can be naturally ejected from your world and need to survive in space. $\endgroup$ Jun 17, 2022 at 15:09
  • $\begingroup$ Half correct, In the context of the question, where the creature is pressured to develop a mechanism to eject itself from its environment. not to rely on accidental occurrences (meteors etc) or just drifting away from an asteroid.Perhaps technickly the answer is ok, but not in spirit. Note the comment from JBH in under the OP, this is possibly the beginning of an answer to to pride food/energy source not available within its biome. $\endgroup$
    – Gillgamesh
    Jun 17, 2022 at 17:45
  • $\begingroup$ @Gillgamesh The aliens in Camelot 30K were pressured to develop an active mechanism to eject themselves, which I explained in the answer--they must travel between worlds, because they will run out of food sources on any individual world, given how slowly they are naturally replenished. They can only do that because they evolved in an environment that made it possible, and occasionally allowed it to happen naturally--small icy bodies with low escape velocity. $\endgroup$ Jun 17, 2022 at 18:20

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