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If we landed a traditional automobile on the moon, the combustion engine would lack oxygen, and, for obvious reasons, would not function. I'm wondering if a planet terrestrial body exists where we would not have to rethink our main method of terrestrial locomotion (being combustion engines).

I would like the answers to focus mainly on atmosphere compositions, not thermal-based problems or other such interference like "the planet is water, there's no surface to drive on". I really am interested what atmospheres would support a combustion engine, if any; any the potential problems with the ones that do (E.G. too much CO2 in atmosphere, would only function at 50% efficiency).

This is not a "should/could we use combustion engines on rovers" question, it's more of a... have we discovered any planets that would support it?

Is there significant information on Trappist to know if any of the planets A-G could support traditional ICE's?

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    $\begingroup$ Are you only lookin for ICEs where the combustion is strictly fuel & oxygen, or would any exothermic reaction of X & ambient atmosphere capable of driving a motor by thermal expansion of gases do? $\endgroup$ – bukwyrm Jun 12 '18 at 18:59
  • $\begingroup$ @bukwyrm seeing as the existing answers address the former, I'd love one on the latter :). Especially if you have information potentially comparing the efficiency of the combustion of the gasses on planet X as compared to combustion of traditional earth composites. $\endgroup$ – Magic Octopus Urn Jun 12 '18 at 19:11
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    $\begingroup$ Knowledge of an extrasolar oxygen rich environment would mean extraterrestrial life is likely to exist, and currently still does, given that free oxygen is highly corrosive. $\endgroup$ – Mazura Jun 12 '18 at 22:05
  • $\begingroup$ I'm pretty sure that life is involved in all known natural processes that could fill an atmosphere with appreciable quantities of oxygen. So discovering a planet with an oxygen atmosphere would be very big news. $\endgroup$ – Emilio M Bumachar Jun 13 '18 at 12:33
  • $\begingroup$ Yes, we do currently know of a terrestrial body with an atmosphere suitable for internal-combustion engines. It's called Earth. You might have heard of it at some point or another... $\endgroup$ – Vikki - formerly Sean Jun 16 '18 at 20:48
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The short answer is no -- an internal combustion engine needs to pull oxygen from the air to operate, and no solid bodies in the solar system have that kind of atmosphere.

Venus' atmosphere is mostly carbon dioxide with a small amount of nitrogen; neither of those is combustible.

Mars, similarly, has a mostly inert atmosphere; there's a trace of oxygen but it works out to about 1/20000 of the partial pressure of oxygen found on Earth -- probably not enough to run a combustion engine.

Titan is an interesting case; there's no oxygen to speak of, but hydrocarbons make up a couple percent of the atmosphere. You could carry a tank of oxidizer -- liquid oxygen or NTO -- in a vehicle and burn it with atmospheric methane, the opposite arrangement to how a terrestrial ICE works. To get a reasonable amount of power, you'd probably have to run very oxygen-rich, which would make for a fairly corrosive exhaust, so you'd need to choose your materials carefully -- you couldn't adapt an existing car engine to it or anything.

As Evan Steinbrenner notes, there are likely to be many planets in other solar systems with an Earthlike nitrogen-oxygen gas mix, where ICEs would work just fine. We don't currently have a good idea how common such atmospheres are, however.

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    $\begingroup$ I love that you touched on Titan, that was my main case for asking the question! I've heard about Titan being really cool (hah! more puns!) in that it has unique atmospheric compositions to most other bodies in our solar system. Was really interested to see if it held potential. That's a neat idea though- providing your own oxygen for the composition and combustion, it seems to be wildly impractical in practice though. $\endgroup$ – Magic Octopus Urn Jun 12 '18 at 19:02
  • $\begingroup$ Do you know if we have enough viable information on the Trappist system to infer whether or not the conditions are close enough for an ICE? I've been craving good Trappist info. $\endgroup$ – Magic Octopus Urn Jun 12 '18 at 19:20
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    $\begingroup$ "there are likely to be many planets in other solar systems with an Earthlike nitrogen-oxygen gas mix": that seems highly unlikely. Oxygen is highly reactive and will not remain in an atmosphere at equilibrium unless there is a non-equilibrium process (i.e. biological processes) to replenish it. Effectively, the presence of Earth-like oxygen levels in an atmosphere is a very good proxy indicator of life. So extra-solar system oxygen can only be as common as extra-solar life. $\endgroup$ – Michael MacAskill Jun 12 '18 at 22:08
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    $\begingroup$ +1 for the engine in Titan carrying oxidizer. However, I disagree that it would need to run oxygen rich or that this would be a serious concern. Our engines in Earth run oxygen rich to improve efficiency of combustible usage, but in Titan they would run combustible rich to improve efficiency of oxygen usage. $\endgroup$ – Pere Jun 13 '18 at 11:56
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    $\begingroup$ Titan's atmosphere doesn't normally contain much hydrocarbons. The 1-2% that's there is below the flammable limit even at Earthly temperatures. You might be able to run an engine from rainfall and stored LOX, though. Alkali metals have been proposed as an energy source for Venus probes, but that was external combustion, a burner heating a Stirling engine. And if you expand the question to allow non-terrestrial worlds, you could use an oxidizer to "fuel" an aircraft flying in a gas giant atmosphere. $\endgroup$ – Christopher James Huff Jun 13 '18 at 21:50
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It seems unlikely in principle

Standard combustion engines rely on burning fuel in an oxidiser taken from the atmosphere. On earth we have an atmosphere which is about one fifth oxygen which does a good job in engines.

We haven't yet observed any planets anywhere with a large supply of oxygen in their atmosphere. And there is a good reason for that. Oxygen is reactive. Things in an oxygen atmosphere burn or oxidise quickly (in fact the specific level of oxygen in earth's atmosphere may be a balance between enough to keep living creatures alive but not so much that fires burn every land dwelling plant every time anything catches fire). So any atmosphere with oxygen in it needs a continuous source of oxygen to keep up the concentration.

Oxygen on earth is a product of life. If there were no life, there would be no continuous supply of oxygen and the concentration would drop until there wasn't enough to support a combustion engine (or fires). Before photosynthesis, earth did not have significant oxygen in the atmosphere (and when photosynthesis became common, geology changed radically with large deposits of, for example, iron oxides suddenly appearing).

So, unless we find a planet that supports photosynthesising life, we are unlikely to find one that supports combustion engines.

Of course other oxidisers are available. But the same objection applies: if they are decent enough oxidisers to support combustion, they will not have a long lifetime in any environment on a geological timescale as they will react with their environment oxidising it and depleting the amount in the atmosphere. So unless you can propose some mechanism to continuously replenish the atmosphere with oxygen (or an alternative) you won't find atmospheres that support combustion. It seem likely that the question has the same answer as "is there any extraterrestrial life". IF we find that we are also likely to find atmospheres that will support engines (and vice versa: if we find atmospheres that support engines, we have found life). But we haven't, yet.

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  • $\begingroup$ Was going to post a "Oxygen is a product of life" answer but you beat me to it by a couple minutes. +1 $\endgroup$ – UIDAlexD Jun 13 '18 at 14:00
  • $\begingroup$ @UIDAlexD feel free to add anything I missed! $\endgroup$ – matt_black Jun 13 '18 at 14:01
  • $\begingroup$ Well I was going to make a joke along the lines of "We've discovered a planet like that, but it's already been explored - even colonized!" joke. Other than that, you said everything I had to and more. $\endgroup$ – UIDAlexD Jun 13 '18 at 14:13
  • $\begingroup$ @UIDAlexD astonished gasping what planet is that?!? (joke) Also, thanks for going more into depth on the "Oxygen is a Product of Life" that the others touched on briefly. Good answer. $\endgroup$ – Magic Octopus Urn Jun 13 '18 at 14:52
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In our solar system? No. None of the other planets would support a standard ICE from earth.

In other systems? We think we've found some other earth like planets which are in the habitable zone which should support ICE's but no one has visited them yet and we lack the ability to directly measure the relevant characteristics.

https://en.wikipedia.org/wiki/List_of_potentially_habitable_exoplanets

Beyond that statistics would seem to say that with the number of stars out there and the numbers of planets orbiting them that there are bound to be some that are close enough to earth that they would support an ICE but currently confirming that is beyond our capabilities let alone actually getting to them.

Also note that ICE's are a really poor option for locomotion unless the other exoplanets also happen to have fossil fuel deposits that could be extracted. Otherwise batteries + solar or nuclear is probably a far better option for locomotion.

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  • $\begingroup$ But Pluto has tons of ICE! Hah! The puns... Thanks, good answer. I was pretty sure planets in our solar system didn't have the conditions other than earth. Was wondering if atmospheric conditions could somehow be remotely approximated on distant stars or something. Even moons like titan wouldn't even remotely support ICE's though? Not just interested in planets. $\endgroup$ – Magic Octopus Urn Jun 12 '18 at 18:54
  • $\begingroup$ I really love both answers, yours for additional external sources and the other for mentioning Titan. I apologize, but is it acceptable to not accept one? $\endgroup$ – Magic Octopus Urn Jun 12 '18 at 19:03
  • $\begingroup$ @MagicOctopusUrn Wait a day or two to see if any better answers come up. If you got something out of Evan's, accept it. I don't need the points. $\endgroup$ – Russell Borogove Jun 12 '18 at 19:24
  • $\begingroup$ @RussellBorogove nobody needs points ;). But I feel you. Thank you both for taking the time to respond regardless. $\endgroup$ – Magic Octopus Urn Jun 12 '18 at 19:28
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Internal combustion is a practical (if undesirable) power source on Earth because there are easy-to-carry, easy-to-store fuels such as gasoline and diesel that can easily be pumped and metered into an engine and reacted with abundant atmospheric oxygen to heat an abundant working fluid (mostly atmospheric nitrogen) to produce mechanical power.

OK, carry your own oxygen and burn with the methane on Titan, sure, but oxygen is hard to store in quantity - you'd be unlikely to attain the sort of energy density with a hypothetical Titan vehicle that we can get here on Earth with gasoline or diesel fueled vehicles.

As stated in other answers, it is, in any event, unlikely you would find naturally occurring chemical reactants in abundance, ready to harvest in any sort of powerplant, on any world unless there was some sort of biological process at work dumping excess energy from some other source (like radiation from a host star) into chemical separation.

Everywhere we have been able to look so far (admittedly only within our own solar system), we find chemical soups on various worlds, but no neatly separated stores of reactants like we have on Earth. Even here we see phenomena like forest fires, triggered by lightning, increasing global entropy combining wood and oxygen to make water vapour, carbon dioxide, and ash. It's just that there's so darn much photosynthetic life that what gets spontaneously consumed by fire is promptly replaced.

The key point is: no celestial body examined to-date has an "exploitable" atmosphere like we have on Earth. As soon as we find one, chances are, we will have found extraterrestrial life.

FWIW: Internal combustion engines are relatively inefficient devices for converting stored energy into mechanical power - at best, only about half the available chemical energy is converted into useful work; the rest ends up as waste heat. They are only practical because of the energy density of the fuel source, power density of ICEs, and the economics of both the devices and the fuels. If you start making chemical substitutions, the economics and practicality can go away, and other options can become more favorable, like fuel cell electric or battery electric.

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  • $\begingroup$ If you can carry the oxygen and burn the ambient fuel, then all the gas giants are also candidates. $\endgroup$ – Hobbes Jun 13 '18 at 14:57

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