# Would it be possible for hunter gatherers to accidentally colonize an exoplanet, from an asteroid knocking a rock containing a cave into space?

I was thinking of a situation, in which a band of hunter gatherers goes into a cave, and while they are in the cave an asteroid crashes into the Earth, causing the rock that the cave is in to be ejected at not only the escape velocity of the Earth, but also the escape velocity of the solar system.

During the brief period of time that the rock is still in Earths Atmosphere a smaller rock gets knocked into the entrance of the cave, sealing the atmosphere of the cave off from the outside universe, so that the atmosphere does not escape into space during the time the rock is in space.

For many generations the hunter gatherers survive by eating the organisms in the cave, until eventually the rock that the cave is in crashes into another planet that happens to have Earth like conditions, and has life.

The rocks that sealed the hunter gathers in the cave for many generations are ejected from the entrance to the cave when the rock crashes into the planet, allowing the hunter gatherers to leave the cave, and colonize the planet.

Would this situation be possible?

• Hector Servadac by Jules Verne, 1877. (French original, English translation.) (Major problem: How come that they are not squished flat by the immense acceleration?) Commented Jul 30, 2020 at 14:03
• No, but it'd make a great story, so write it anyway! Commented Jul 30, 2020 at 14:19
• No. No, no, no, no, no. Nope. Not at all. No. Oh, no no no no no. ... But I'm with @workerjoe, don't let that stop you from writing the story. And to everyone who tells you that what you've written is impossible I say, "fine, buy a textbook. You'll enjoy yourself more."
– JBH
Commented Jul 30, 2020 at 15:35
• Sure, if your hunter-gatherers are actually microscopic animals such as tardigrades, then it could happen. Commented Jul 31, 2020 at 12:41
• @DWKraus Didn't Star Trek TNG kind do this, although with teleporter, holodeck, and warp speed to a new planet? The race would have died on their home planet, but couldn't be told about the Federation. The group was led into a cave, transported into a holodeck image of the cave, where they traveled through a (fake) extensive cave system until the Enterprise arrived at a new planet. Then they were transported to a cave on the new planet, where the existed to a new safe world. Commented Jul 31, 2020 at 14:04

The rocks that ceiled the hunter gathers in the cave for many generations are ejected from the entrance to the cave when the rock crashes into the planet, allowing the hunter gatherers to leave the cave, and colonize the planet.

Would this situation be possible?

Very likely not at all, for a series of reasons:

First:

The large chunk of rock with a cave inside will be drifting in space moving outside of the solar system. This means it will be far from one of the two energy sources we have on Earth, namely sun light.

The other one, radioactive decay, might be present, but I am afraid that if it intense enough to keep the rock at livable temperature will soak anything inside that rock into a shower of radiation which would quickly sterilize any form of life.

Second:

Lack of light, gravity, scarcity of water and exposure to space radiation will again sterilize any life form in the rock, except maybe some spores.

Third

For any realistic ejection velocity, it will take millennia to reach the closest star. And even assuming, ad absurdum, that they manage to survive the whole trip, they have no means of dissipating the enormous kinetic energy that they have. This means that the crash landing they will perform will be very, very crash. So crash that they will reach the planet surface in form of individual atoms after being transformed into plasma by either atmospheric heating or surface impact.

The faster you make them escape from Earth to shorten the trip, the faster they are going to hit the ground when they land.

• Don't forget that, barring panspermia, the life on the other end is likely incompatible! Okay, this Q is fun because of it's holes. The real challenge would be to figure out how to make it work... Commented Jul 30, 2020 at 14:19
• #3 also works in reverse. To depart, you need an impulse that totals to more than the escape velocity of the originating rock (Earth). All in one go. Commented Jul 30, 2020 at 14:46
• They do have means to dissipate interstellar kinetic energy, that is through an extremely lucky series of gravity assists. Even in the best case, they'll still need to dissipate the first escape velocity of their destination. They can aerobrake, but that alone requires a bit of luck - and possibly good thermal insulation for the astronauts. Commented Jul 30, 2020 at 14:50
• Simple answer is just no. Not going to happen, not possible. Shame as it would be fun. Commented Jul 30, 2020 at 15:54
• @JBH To be fair though - They survived impulse acceleration to escape velocity (somehow). Even with severe osteoporosis, landing at the terminal velocity of a large cave should be a breeze. Commented Jul 30, 2020 at 16:02

Unfortunately, such a plan would be doomed from the start.

It's not enough to simply reach escape velocity while on Earth's surface, because Earth has an atmosphere that will quickly slow you back down again. Rockets counteract this with continual thrust, but for a system with a single impulse - such as a space gun or being knocked into space by an impact - it needs to have a velocity so high that even after accounting for atmospheric drag, enough velocity remains to escape. And it needs to gain all of that velocity more or less instantaneously.

The upshot of this is that your cave will undergo G-forces many times more ferocious than being shot out of a cannon, forces so strong that they'll pulverize anything living inside it. They'll be dead long before considerations of the cave's heat capacity or structural integrity come into play (it could easily be torn apart - and that's all before it even leaves the atmosphere in the first place).

• I suspect that some bacteria might survive but that's about it Commented Jul 30, 2020 at 15:52
• Yep, everyone is dead on launch. The space shuttle accelerates at human-survivable levels for several minutes to get to orbit. The acceleration from an asteroid impact will take place over a fraction of a second, resulting in a g-force hundreds or thousands of times greater than a rocket launch. Commented Jul 30, 2020 at 18:29

ALIEN ABDUCTION (circa 20,000 BCE):

The only way this scenario works that I can see is if there is an intervening intelligently designed space traveller involved transporting the people. It could certainly LOOK like this to the people in the cave; if they understood enough of it to make cave drawings, passing on the story to ancestors, then this could be their narrative.

The aliens (motives unknown) seal the people into a cave, excavate the entire cave from it's surroundings, and lift it up into their ship, carrying it to an alien world. It's alien tech, so we don't need to worry about the cave collapsing, etc., I'm sure they would compensate. I'm pretty sure it doesn't need to take generations. It could be minutes, hours, etc. but more than weeks and the aliens would need to supply food. The end planet would need to be compatible with earthly biology, but we are already having alien-driven panspermia, so this doesn't need much handwaving.

BOOM! Your cave people are on an alien world with them no wiser about why. They can mythologize anything you want.

• For one depiction of this, see Star Trek TNG episode Homeward Commented Jul 31, 2020 at 7:47
• +1: Xeno ex machina Commented Jul 31, 2020 at 15:28
• There are lots of SF stories where early advanced alien civilizations visit Earth in its prehistory and 'transplant' early humans (and other parts of the then existent ecology). If you want to make the story believable simply make the 'cave' and the 'fire' of lift off from Earth and landing on the new world a common creation myth like the flood myths of Earth based on actual geological floods. Regardless of where the original colonists were collected from they would then all pass on similar stories to their offspring, regardless of where they ended up being transplanted to on the new world.
– Mon
Commented Aug 1, 2020 at 11:16

You can actually do an experiment to verify what would happen.

All you need is a modern artillery piece, say for example the US155mm M109A7 mechanized artillery tube.

Then you design a 'special' heavily reinforced hollow artillery round (so it doesn't break up upon firing or impact) that can be unscrewed to allow access to the hollow core.

Into this core you place half a dozen live mice.

Having done that you then place the round inside the artillery piece and load the round together with maximum number of charge bags. After which you fire the round at a per-determined location consisting of deep, relativity soft soil from which the round can be recovered.

You the recover the (hopefully) intact round and conduct an examination of the occupants.

Following this inspection you can place the resulting 'mouse pate'(slightly warmed) on a thin bit of toasted crispbread, sprinkled with fresh herbs and parmesan to be consumed at your leisure.

• I find that when making mouse pâté in this manner that it is best to use 'pinkies' as the fur of full grown mice tends to stay largely intact, and most people find this imparts a distasteful texture to the pâté. Commented Jul 31, 2020 at 12:59
• Mouse mousse, anyone? Commented Jul 31, 2020 at 16:51

Lots of great problems with this have been mentioned already, but I'll add a couple more:

Rock Porosity

Caves generally form in pretty porous rocks (that's how all the water got in to form it in the first place). You can bet that the vacuum of space will suck all the air out pretty fast.

Not Enough People and/or Food

I'm seeing different estimates but you'd need over 100 people to repopulate humans on another planet. A hunter-gatherer needs around 40 ha to support itself and caves are relatively unproductive areas so multiply it by a factor of I'd say well over 100. But you're also not replenishing from energy sources like the sun, geothermal energy, and chemical energy coming in from the outside. So I wouldn't bet on them living much past however long it would've taken for them to starve to death anyways.

• @quetzalcoatl thanks for the catch, and sweet username Commented Jul 31, 2020 at 2:15

Nobody has yet mentioned oxygen.

In normal air that's 20% oxygen, we humans breath about 11 cubic meters of air a day each. With no sunlight, there will be no photosynthesis to convert CO2 back into O2 (or, of course, to be the bottom layer of the food web). So all the oxygen they breathe will need to be in the cave at the start. Even if you get past all the other very serious issues others have mentioned, this one is going to keep your journey very short.

That isn't to say you shouldn't write the story. If you have an interesting situation or thought experiment, readers will often tolerate some seriously implausible events needed to create it. (Eric Flint's 1632 or "Ring of Fire" comes to mind.) But it's better to admit the backstory is implausible than to try to hard to justify it.

Surprising, haven't seen this mentioned yet: After a few months, much more certainly a few millennia, the entire rock is going to be at a temperature of only a few Kelvin. All other considerations aside, I doubt your cavemen will have much success keeping it any warmer. Even if they could somehow build fires (& not die of carbon monoxide poisoning, or run out of oxygen, or run out of fuel) to make it warm, you're going to have to warm the entire rock lest all the heat be sapped out through the frozen cave walls. At the temperatures the rock will adopt, your very atmosphere will be condensing on the cave walls, and touching it will frost-burn you very rapidly. Keeping the internal cavity at reasonable temperatures means continuously resupplying the heat that the rock will be radiating the whole time.

Interesting note (because you should write this story), such radiation would be fairly distinctive & who knows, maybe somebody will spot the weird microwave-emitting asteroid when it gets close enough to a sensor to detect.

To answer the original question: No, asteroid impacts could not enable human interplanetary travel. The acceleration involved at each end is too great for anything other than bacteria to survive, not to mention the extended journey through the cold and dark of space.

Here is a less implausible scenario: Instead of an impact, there is a near miss between two planets. They are briefly close enough that the two atmospheres are connected. In the narrow gap between the two planets the two gravitational fields nearly cancel out. The net gravity is so low that a violent storm picks people up and deposits them on the other planet.

To be clear, this scenario is still quite dubious. There are several issues -- the relative velocities, the tidal forces, and figuring out the orbital mechanics of such an interaction. (Perhaps a third or fourth planet/moon would be needed to make it work.) But I think this near miss is more plausible than a violent impact.

If you want to make this work, even though it's very unlikely, here are a couple things you can do:

• Make the cavern system out of an extremely dense, non-porous, and contiguous rock
• Make it so that when this rock is ejected into space, it is spinning rapidly. This causes internal artificial gravity, although for this to work, the rock needs to have an unnaturally high tensile strength
• Make the cavern large enough to support a rather large underground lake, and make sure that lake has plenty of plant and animal life to start off with
• If you want to make the humans inside have any idea of what's happening, maybe give them a window in the form of a very large crystal. Perhaps, this crystal is why they were in the cave in the first place (eg religious site), and a couple meters of mostly clear quartz could give them a good view into space and maybe even provide some sunlight
• You'll probably need to engineer some sort of plant which performs CO2 --> O2 conversion without sunlight. Maybe have them feed off certain minerals found in the cavern systems
• Have your humans start out with an extremely large food supply. Maybe, they've been storing food in this cavern for years or decades for religious reasons or whatever. They need a lot of biomass
• Besides plants and animals, use fungus for consumption and possibly light in the form of luminescence
• Include some chemicals or minerals which can be used to create heat through an exothermic reaction. The humans can mine this material and use it for light, heat, and cooking instead of fire
• Don't make the journey too long. The humans would survive a couple generations optimistically; not nearly enough to make an interstellar journey. Maybe have them crash on another planet or moon in the same solar system. That type of journey could be measured in months, years, or even decades
• Landing is difficult. The target planet or moon needs to have a very thick atmosphere and the rock needs to come in at a very shallow angle. Maybe, have it aerocapture and orbit a couple times, each time slowing down more and more to prevent the humans from becoming pasted or cooked.
• To survive landing, humans will want to wait until reentry of the rock is over and the rock reaches terminal velocity. Then, ideally, they'll be sucked out of the rock when it breaks up in the atmosphere. After that, they skydive (without parachutes) and hope to survive. If they're able to land in vegetation, it's possible to make it with only a few broken bones.

As you have already seen, the answer to your question, as originally posed, is a big, fat "no". Do you have the scope for a rather long story or even series or stories? If so, why not combine some of the alternatives suggested with an overarching "discovery" narrative:

• The planet is under asteroid bombardment in advance of the big, big comet that's arriving soon.
• Benign aliens have spotted the unsophisticated but intelligent hunter-gatherer (HG) life on the planet and don't want to see it die out.
• The aliens find that a group of HG's are (not unreasonably) sheltering in a cave and fake a random rock impact to seal it up, then lift the whole cave, intact, from the bedrock (with authentic-feeling shaking and noise) using tractor beams, a transporter, drones, whatever and take it to the ship where it remains sealed, with the HGs being put into slow mode so they think they've been there years.
• Cave deposited roughly (but survivably) on a biologically-compatible planet with no existing intelligent life.

After this, the population of HGs grows, over the millennia, into the planet-wide dominant species, with the "smashed out of their own world" myth as their dominant religious foundation story, which no-one believes literally any more, but think of as a great metaphor for their elevation from primitive to civilized status. Eventually, what's left of the original cave is found buried in the desert (like all good relics) and one or more of the finders begin to question whether there was any sort of truth behind the original "myth" and start looking for answers. Throw in the aliens still being around to keep an eye on their "project" and you have as long a story as you can (or want to) carry off.

I've read (and paid for!) books with more far-fetched plots.

Although a conventional interstellar travel is unlikely, due the the crushing forces of the impact, there may be a potential to involve wormholes and some strange physics. If the wormhole is the gravitational cause of the asteroid, or it just manages to rapture some poor folk in caves and eject them conveniently on another world there may be something to work with. I'm no expert in wormholes.

Sort of like Stargate without the teleological root cause.

• Unfortunately most theories for wormhole formation and stabilization indicate they would have too much radiation and gravitational force to be safe for humans. Commented Jul 31, 2020 at 14:01
• Yeah, it seemed like a stretch Commented Jul 31, 2020 at 14:09

As shown here, it won't work all that well. To be launched into space you need a massive impact. An impact smaller than the KT impact that wiped out the dinosaurs would not be sufficient to launch ejecta beyond Earth's orbit. And even the KT impact did not produce all that much ejecta that escaped Earth's gravity.

Lunar scientists expect to find traces of the Earth rocks on the Moon blasted from the Earth's surface during the Late Heavy Bombardment period. But the impacts that happened around that time were many orders of magnitude larger than the KT impact. Take e.g. the Imbrium impact

Around 3.8 billion years ago, an asteroid more than 150 miles across, roughly equal to the length of New Jersey, slammed into the Moon and created the Imbrium Basin — the right eye of the fabled Man in the Moon. This new size estimate, published in the journal Nature, suggests an Imbrium impactor that was two times larger in diameter and 10 times more massive than previous estimates. “We show that Imbrium was likely formed by an absolutely enormous object, large enough to be classified as a protoplanet,” said Pete Schultz, professor of earth, environmental and planetary sciences at Brown University. “

The Earth was around that time also pummeled by objects of this size and even larger, as the Earth is a much larger target than the Moon. It are impacts of this size, about 5000 times more energetic than the KT impact, that launch a large amount of material beyond Earth's orbit.