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Subterranean : existing, situated, or operating below the surface of the earth; underground.

Informally, we can use subterranean to describe that which lies below the surface; technically, terranean refers to terra, the Latin name for Earth.

What word could we use to mean that which lies below a surface, in general. I.e., what would we say about caves under the surface of Mars, "submartian"?

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    Well, there's "earth" the substance, and "Earth" the planet. One could make the case that there's lowercase-e-earth on Mars, for instance.
    – Doug Warren
    Dec 7, 2016 at 21:46
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    For what it's worth, sci-fi writers have from time to time used "sublunar" to mean "underground on the moon". E.g., from Jack Williamson's story "The Equalizer" in Astounding Science Fiction, March 1947, p. 18: For the actual fort was far beneath the crater. A vast web of tunnels sheltered hangars, shops, barracks, and magazines. The launching tubes, trained forever on the Earth, were hidden in deep pits. Somewhere in that sublunar labyrinth, we could hope to find our riddle answered.
    – bof
    Dec 8, 2016 at 9:35
  • Possibly some form of the word lithos might serve (see also “lithobreaking” = crashing into the planet’s surface), but the answers below indicate “subterranean” is the accepted usage.
    – J. C. Salomon
    Dec 9, 2016 at 0:07
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    @Bof, yes, of course. But it’s a typo that kinda works.
    – J. C. Salomon
    Dec 9, 2016 at 0:23
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    Why not just use "subterrainian"? Like terranean, but for generic terrain.
    – ArtOfCode
    Dec 10, 2016 at 14:31

8 Answers 8

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This question is predicated on the wrong definition of "Terra". As seen at Wiktionary:

  1. ground, dry land
  2. earth, soil, dirt

That is, not "Earth" (the planet) but instead "earth", meaning "dirt" or "ground".

So, subterranean is acceptable to describe anything underground, whether under the surface of Planet Earth or not.

Edit: I would not suggest using "subsurface" unless it was acceptable to include underwater things such as a submarine.

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  • 6
    Wiktionary is a questionable resource.
    – Mitch
    Dec 7, 2016 at 23:39
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    @Mitch You will need to prove that the actual definition there is questionable.
    – Spencer
    Dec 7, 2016 at 23:43
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    I agree with @Spencer and feel this is backed up by etymology: terra - literally "dry land" (as opposed to "sea"); from PIE root ters- "to dry" (source also of Sanskrit tarsayati "dries up," Avestan tarshu- "dry, solid," Greek teresesthai "to become or be dry," Latin torrere "dry up, parch". So terra could refer to the dry surface of any planet or satellite. With all that said, I also feel subsurface would do just as well.
    – Randy Tillman
    Dec 8, 2016 at 1:32
  • I imagine when you have earth in a circuit on Mars you'd probably still call it earth.
    – user4683
    Dec 8, 2016 at 9:14
  • Maybe subtellurian (under planet Earth (Tellus)) should refer to the planets that are inferior to Earth, i.e. Venus and Mercury. In what other way could you be "underneath" an entire planet?
    – Jeppe Stig Nielsen
    Dec 10, 2016 at 12:06
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NASA uses subterranean, as in this press release:

NASA’s Hubble Space Telescope has the best evidence yet for an underground saltwater ocean on Ganymede, Jupiter’s largest moon. The subterranean ocean is thought to have more water than all the water on Earth's surface.

Granted, the OP asked for an alternate to subterranean, and NASA is perhaps not a leading expert in English, but subterranean seems preferable to a plethora of words specific to every planet and moon on which underground water might be found. This is especially so now that exoplanets are being found in great number, and the technology to find out if water exists on or inside them is sure to be developed, if it has not already been.

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    It's surprisingly bothersome to me that NASA used that term. Not that I want them to use "subganymedean," but why not "underground" or "sub-surface?" Sigh.
    – Katherine Lockwood
    Dec 7, 2016 at 21:41
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    @Katherine Lockwood Their budget doesn't allow for a linguist until they discover aliens. :) They probably used subterranean in the second sentence because they used underground in the first sentence.
    – ab2
    Dec 7, 2016 at 21:43
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    Planetary scientists refer to the terrains of alien worlds pretty regularly. "Subterranean" always sounded like a word to describe stuff that sits below the terrain, to me. I think that the trick is to remember that when people spoke of "terra" several thousand years ago they weren't necessarily referring to Terra, the planet that you hear about in science-fiction stories. "Surface" is actually an incredibly vague term when you start talking about things in the sky too, to be totally honest.
    – Chib
    Dec 7, 2016 at 21:45
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    The latin word terra classically means earth (little e) as in earth, ground, land, country, or an area. Not big "e" Earth. Sub terra (subterranean) is simply under ground, or under the earth.
    – Clinton Pierce
    Dec 7, 2016 at 23:32
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    I think that Latin refers to uppercase Earth as "orbs terrarum", which further supports the claim that terra does not refer to the planet, but rather means "earth" or "land". I think it's appropriate then to use the word "subterranean" to describe places on other planets.
    – ktm5124
    Dec 8, 2016 at 0:51
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You may use underground:

  • occurring, situated, or used below ground level: an underground tunnel; an underground explosion.

Collins Dictionary

From: www.space.com:

  • A new study suggests that water also flows on the surface. ... local, or only underground on Mars.

From: www.sky.com:

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  • Yes, ground (whose Germanic etymology seems related to "foundation") would seem universally applicable - whilst earth - meaning "soil", of course wouldn't. One could hardly speak of "Martian earth"!
    – WS2
    Dec 7, 2016 at 21:43
  • ...although the OED gives The ground considered as a solid stratum.
    – Dan
    Dec 7, 2016 at 23:03
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    @WS2: Hmm, that begs the question .... what is the Martian equivalent of "earth"? "Mars"? "I let the pebbles of mars trickle through my gloved fingers" hmm nah
    – Lightness Races in Orbit
    Dec 8, 2016 at 0:38
  • @LightnessRacesinOrbit well, I wouldn't use "pebbles of [lowercase-e] earth", either. In my mind pebbles are lumps of stone, not of earth (though earth may contain pebbles...). For uppercase E I'd only not use it because I've yet to need the distinction. As for the sense of what was meant, "the lumps of [Martian] soil" works fine in my view.
    – Darael
    Dec 8, 2016 at 16:51
  • @Darael: You know what I mean. Yes, of course, we can avoid the issue entirely by using a separate category of term. That's not in the spirit of what I was asking.
    – Lightness Races in Orbit
    Dec 8, 2016 at 17:12
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Subterranean or Underground are perfectly acceptable usage for other planets or moons composed of rocky material.

As indicated by others, terra frequently refers to earth as in soil or land, rather than Earth the planet.

Earth is not the only planet that shares its name with a substance (Mercury does, too, but in that case it is a coincidence whereas in the case of Earth it is not.)

There are many words and phrases based on the root terra-. These include terracotta, terra firma, terrace and most tellingly, terrain. If we cannot use the word "subterranean" to refer to underground features on Mars, then by the same logic we cannot speak of Martian terrain and the position becomes absurd.

In fact the four inner planets of the solar system are said to be terrestrial planets, meaning they are composed of earth and rock.

The situation is different for gas giants, such as jupiter, or bodies composed largely of water / ice such as Europa or Titan, which have an ice crust. The latter are believed to have a subsurface ocean rather than a subterranean one. (They also are believed to have features analogous to volcanoes where molten ice rather than molten rock is spewed out. These are known as cryovolcanoes.)

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This distinction doesn't seem useful to me. Furthermore, as Spencer points out, it is based on false premise: the question implicitly assumes that terra is only "the Latin name for Earth". In fact, it is also the Latin word for earth. Dirt, ground, or dry land. Mars may not be "Earth", uppercase-E, but it certainly has "earth", lowercase-e.

I don't think it even makes sense to interpret the terra in subterranean as meaning "Earth". Are subterranean structures "beneath Earth" (the planet as a whole)? No, they aren't. The Earth's center of gravity is a point inside the planet, so nothing can be beneath it. Subterranean structures are beneath earth.

The same confusion in French has led to the coinage of some silly words like amarsir "land on Mars" (by analogy with atterrir "land" on dry land)" and amarsissage, but these words are not necessary and are not favored by official organizations, as explained in the following Le Monde blog post "DICO – Doit-on dire « amarsissage » ou « atterrissage sur Mars » ?":

Les experts soulignent que l’apparition de ces néologismes est dû à une confusion : la racine d' »atterrissage » ne désigne par la Terre, la planète, mais bien la terre, l’élément. Il n’y aurait donc pas de sens à parler d’un « amarsissage » puisque, même sur Mars, le robot s’est posé sur de la terre.

(My translation: "Experts highlight that the appearance of these neologisms is due to a confusion: the root of "atterrissage" doesn't designate Earth, the planet, but earth, the element. There is therefore no sense in speaking of "amarsissage" because, even on Mars, the robot rests on the earth.")

If you restricted all terms with roots like this to their original, terrestrial references, you'd also be unable to speak of "oceans" on any planet but Earth since the word "ocean" comes from the same root as the Greek personification of the ocean "Oceanus". Oops! Tell that to the people writing about a hypothesized "ocean" of Jupiter's moon Europa. (Or should that be "a sub-surface body of water on Jupiter's satellite Europa"?)

In fact, I found that the actual word "terra" itself (or the plural "terrae") seems to be used in astronomy to refer to particular regions of the moon that are rocky or rough.

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A generic term would be 'subsurface' (MW adjective)

of, relating to, or being something located beneath a surface and especially underground

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Perhaps a slight turn of thought (and just a touch of fun) is required. We could drop the Latin for some of the planets and look at Greece for the original names of the Roman gods chosen to represent them. On the other hand, just one of them uses a Latin derivative, as with "Jovan moons," "Jovan asteroids," and "Jovan LaGrange points" (by Zeus ... I mean, Jove). From the late 14th century, Jove had become a poetic term for the planet Jupiter, stemming from the Latin Iovis.

From the inner orbit outward:

Mercury might take sub-mercurian/sub-mercurial or sub-hermitian (very doubtful on the last one – a bit rough on the artistic flow).

Venus might prove difficult using the Greek Aphrodite, and sci-fi writers have already leaped upon the term Venusian (capitalized). It sounds pretty solid.

I'm sure a truly 'solar' language will have to glimpse some of the original Greek. I found that NASA did just that when I visited some of their many informative pages regarding the planet Mars. There, they used the term areocentric to describe a Mars orbit. Roman Mars equals Greek Ares, ergo areocentric. The word seemed to flow for me with a pleasant grace. In this venue, could underground on Mars become sub-arean? The term terrain might even reach as far as, dare I say it ... areain...?

For Jupiter, it seems to be stuck with Jove, a Latin derivative, so below the surface clouds of Jupiter might be found sub-Jovan (capitalized again).

Saturn will likely stick with Saturnine (so many capitalizations) cloud cover and, therefore, sub-saturnine (NOT capitalized - yay!).

The sniggering joke of the planets, Uranus, is already linked to Uranian.

Apparently, Neptune may go either way, with the accepted adjectives Neptunian and Poseidean.

Pluto, our newest non-planet (aka dwarf-planet) already uses the adjective Plutonian. Considering the Grecian Underworld to be the home for both Heaven and Hell in Greek mythology, might sub-Seventh Heaven also apply? Sub-Cloud 9? Naw. Just sub-Plutonian (capitalization required).

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You can use creative liberty with the prefix sub. Subglacial, Subterranian, Subatmospheric, Subsurface, sub-lithospheric and underground, subaquatic, sub-benthic, sub-volcanic, sub-magmatic, speleogenesis ... If a new kind of planetary surface exists which requires a new description, you can use sub/under to describe it. Before describing the subsurface of new types of surface, the surface must be defined: Sea is used to describe a lot of things which are not water, and ice is used to describe CO2 ice, so terrain for the moment is a very suitable term for land surface.

When i need info like this i check out "mining/cave glossary" on google.

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