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.