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I'm imagining a world much larger than earth, with very compacted soil. This planet also has no sun, so a lot of the life exists underground.

My querie is: how reasonable is an animal that is effectively a drill? that is, it's entire body rotates to move through the ground. I'm not sure on how energetically feasible this would be, although it's the best way we've figured out.

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  • $\begingroup$ How big of an animal are we talking about? And ha fast and deep should it drill? $\endgroup$ – Achilles Nov 13 '16 at 16:10
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    $\begingroup$ Possible duplicate of Sea creature moving via rotational motions - this question basically boils down to the same question as duplicate, which is: How reasonable is a circular rotational part on an Animal. The answers also happen to answer this question. $\endgroup$ – Aify Nov 13 '16 at 19:02
  • $\begingroup$ The medium is the message. Motion through the ocean is easy and normal; rotational motion not so much. Compact soil is a different proposition. @Aify concentrates on the rotational motion part of what was his question, cited as the duplicate, but doesn't factor in soil as the medium. Related question, certainly! A duplicate? No. $\endgroup$ – a4android Nov 14 '16 at 3:44
  • $\begingroup$ @a4android This question asks specifically for a drill, which requires rotational motions. My question specifically deals with rotational movements on creatures, and seeing as a propeller could be turned into a drill if you replaced the fins with a drill head, the answers on my question answer this question. The accepted answer of my question adequately answers this question as well. Use Symbiosis. $\endgroup$ – Aify Nov 14 '16 at 4:20
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    $\begingroup$ @Aify. Use Symbiosis? You've lost me. One big difference is the energetics. A soil-drill organism has to generate several orders of magnitude more energy to bore through the ground. This means a lot more than simply a creature rotating its body. Drilling is a non-trivial exercise. Seawater is a fluid medium, compact soil is a solid. The bio-materials of its body will be radically different too. These are entirely different problems of scale. If it was simply about rotational motion = drilling, this is a duplicate, sure thing. It's not, IMHO. $\endgroup$ – a4android Nov 14 '16 at 7:22
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If the planet has no Sun, there will be no energy reaching it as sunlight. No photosynthesis, no plants, no herbivores. What are the alternative sources of energy available? Geothermal. Natural radioactivity. Organisms living on the planet either have to "power" their metabolism by staying close to geothermal areas such as underground "hot-spots" or by ingesting radionuclides to drive their biochemistry.

If the planet is larger than Earth it will, presumably, have higher gravity (although, as this is an assumption, will be dependent on the planet's density). Gravity will help make the soils compact. Because there is no Sun, it will be extremely cold. The soil will be more than compact it will be frozen sold into a cryogenic permafrost.

Deep subterranean lifeforms, that is organisms living kilometres deep in the earth, are known on our planet. There is an open question about whether those organism first evolved on the surface of the Earth and then migrated underground or whether they evolved down there in the first instance or it is combination of both. Deep life evolving down below and is then joined by migrants from above. The point is organism can exist deep underground. However, they are micro-organisms.

Not unsurprisingly, microbes do not need to drill their way through the earth. They infiltrate cracks, crevices, any gaps between particles of soil, and move very slowly. This is an extremely low-energy ecology. The organisms are capable of long periods of hibernation and inactivity. Their only feedstock is organic matter embedded in the matrix of soils and rocks and the presence of methane.

Multicellular organism do not exist at these depths. There isn't the available to support their existence. This is apart from the energy required to drill its way through compact soil.

A drilling organism will require more energy than any known animal on Earth to drive its body through compact soil. The soil on your hypothetical planet will be cryogenically solidified as well. There are no ready sources of energy on a sunless planet to provide the fuel needed for a drilling animal.

There is already a question that addresses the issues about an organism with rotational motion Sea creature moving via rotational motions. Although that only deals with marine organisms moving rotationally through a fluid medium. Moving through a solid medium is a completely different order of magnitude. The mechanics of its moving rotationally are trivial by comparison to the biological requirements for an organism to be able to move through solid matter.

The creature would need to have a drill-head composed of materials that are stronger than diamond. Admittedly the creature might gather the diamonds to fit them together to form its drill-head, but it would have to drill its way through the soil to gather the diamonds in the first place. A chicken and the egg problem.

Depending on the size and mass of the drilling animal, this will determine how much energy is required to propel it through solid matter. The bigger and more massive the animal the more biological energy will be required. The energy required to drill will be of orders of magnitude greater.

The drilling creature could be the biological equivalent of a subterrene. Let's start by considering the fictional subterrene.

Fictional subterrenes are often depicted as cylindrical in shape with conical drill heads at one or both ends, sometimes with some kind of tank-tread for propulsion, and described either as leaving an empty tunnel behind it, or as filling the space behind it with mining debris. The plausibility of such machines has declined with the advent of the real-world tunnel boring machines, which demonstrate the reality of the boring task. Tunnel boring machine themselves are not usually considered to be subterrenes, possibly because they lack the secondary attributes - mobility and independence - that are normally applied to vehicles.

That is the vision for fictional subterrenes, but this is what required for real-world subterrenes.

A real-world, mobile subterrene must work thermally, using very high temperature and immense pressure to melt and push through rock. The front of the machine is equipped with a stationary drill tip which is kept at 1,300–1,700 °F (700–930 °C). The molten rock is pushed around the edges as the vehicle is forced forward, and cools to a glass-like lining of the tunnel. Massive amounts of energy are required to heat the drill head, supplied via nuclear power or electricity. Patents issued in the 1970s1 indicate that U.S. scientists had planned to use nuclear power to liquefy lithium metal and circulate it to the front of the machine (drill). An onboard nuclear reactor can permit a truly independent subterrene, but cooling the reactor is a difficult problem.

It is extremely improbable that a nuclear-powered organism could evolve to extent that it develop into a biological drilling mechanism. Generally it can be considered that drilling animals are impossible. At least, not large sized multicellular organisms. This is a reductio ad absurdum type of answer where the requirements of what would it make work is pushed to its extremes to see why it wouldn't work.

However, it is possible to conceptually consider what sort of organism might be able to survive and move through compact might be. Subterranean micro-organisms are possible. They will be extremely exotic organisms, their biochemistry and metabolism will be radically different from Earth micro-organisms because its habitat is a cryogenic permafrost.

As said above, these organisms will either live in geological "hot-spots" or they will digest radioactive materials whose emissions will "power" their metabolisms. It is possible these creatures could exist in colonial forms, not just as individual microbes, and these colonies could seep and ooze their way through the interstices of the soil. Very slowly. Microbes may not be the most exciting lifeforms, but they are ninety percent of all life on this planet. Quite easily they could be one hundred percent of the life on your sunless planet.

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A drilling motion with the entire body rotating is possible but unlikely. What is more likely is that some form of mouth or limbs at the front do the digging and the rest of the body just follows that through the hole.

You can look at earth's burrowing animals such as moles and earthworms for inspiration:

Moles: http://www.nytimes.com/2014/01/28/science/uncovering-the-secrets-of-mole-motion.html

Earthworms by contrast actually eat their way through the soil. They ingest it at the front and then as they slowly move their way forwards they excrete it at the back.

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For one thing, it seems that continuous, rotational motion would be impractical. However, perhaps oscillating, rotational motion would be one possible approach. This way a dedicated mid-section (near the head) of the creature could contract lengthwise and expand its girth ( similar to what a muscle does when it contracts) so as to anchor itself inside the hole. This is the same principle used to anchor hardware into concrete or drywall.

This would require very little energy other than what is needed to generate some modest pressure over an area, in contact with the walls of the hole. It would work best with some kind of flexible exterior, a leather like sheath around a portion of the creature, but with a hardness gradient - say kind of like a leather shield plate with a bone hand grip. Not two pieces, but one which transitions, in it's properties, from something like hard leather on the surface to sturdy bone underneath. This way the anchoring could be accomplished in a manner similar to the way a mantis shrimp "cocks" it's club-fist with an internal ratchet mechanism so it is locked in place. Then the mantis shrimp flexes its powerful arm to generate accelerating force, then it releases the latch on it's internal locking mechanism and the arm launches like a jack hammer - short but explosively powerful.

The similarity that would benefit your creature is the locking mechanism, but rather than locking up internally before anchoring it's body, it would flex to anchor itself, then lock it's mechanism so it wouldn't have to hold that flexed position, but could relax and stay firmly anchored in the hole.

Then it could twist back and forth at its head, in an oscillating manner to generate a grinding force at the base of the hole. I'm sure you are familiar with Dune and Tremors, so I won't go heavily into detail about the head and grinding mechanism, but you will probably want something like limpet sea snail teeth covering small pads for slowly wearing down rock or other impediments - this would be the most like drilling.

And you will want some other kind of mechanism for moving a lot of looser soil. Perhaps the creature would have a lot of pick like appendages like a crab. Long, sharp, pointed actuators, perhaps mostly originating forward, but hinged with the pointed tips angling from the front of the creature to the back - opposite the direction the creature prefers to move through the hole. This, with some variations on the appendages and their particular tips, and perhaps at different locations on the body for different purposes - would allow the creature to shuttle all of the refuse from the dig around it's body and behind it, so it could continue forward as it digs.

The issues your creature would face would be extreme heating of rock when cutting into it, but perhaps it would only prefer to cut rock when the surrounding earth is sufficiently wet or even seeping near a source of water. Then it could take it's time and intentionally cut out its chosen burrow into the safety of rock where it would only have to defend the entrance against intruders and would otherwise have plenty of warning if any intruder did come (from any direction).

Otherwise it needs calories, lots of them. Digging is very hard work. Maybe it is aquatic and hides at a perch in a hole at the bottom of a cold underground ocean where its choice of prey is a thick and very fatty creature, so it can get enough energy to bore through its world.

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You have a slightly larger problem, which is - how do you have life at all on a planet with no sun?

If you had some geothermal activity on an ocean floor, you could conceivably have life evolve, at least to the level of worms and such, but without warmth from the sun, life would not be able to colonise the land masses. It would have to stay close to its source of energy.

Drilling in the ocean floor in those areas might be a possibility ...

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I could see a worm with two curved hard plates something similar to shipworms, just with offset plates and a twisted motion. the question is why are they burrowing in hard soil? there will not be a lot to eat in compacted soil, since compacted soil doesn't have much in the way of spaces for water and air that things need to live.

I am thinking a digging apparatus something like an antique post hole digger crossed with a bunghole auger. with a motion where they push forward with a slight twist slowly carving away the soil. energetically it not that different than normal burrowing, you might need to give the worm so form of soft cartilaginous pseudo-skeleton in order to generate the torque.

but you really don't need to have no sun to have things live underground there is life for miles under the earth's surface.

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Your creature should look like this:

Drimogemon

For more information:

http://digimon.wikia.com/wiki/Drimogemon

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  • $\begingroup$ And how does it work? $\endgroup$ – dot_Sp0T Nov 13 '16 at 17:45

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