The Earth is full of interesting geographical features-- you know, the kind you’ve all
seen on those posters that show you what they’re all called-- things like coves and estuaries
and plateaus and peninsulas and canyons and all that stuff, but what about on other planets
and moons?
They’re just as geographically varied as the Earth, but scientists who study them generally
use different names for them, so how many of you know what a planitia is, or a chasma,
or a vallis?
Hello everyone, this is your weekly dose of geography.
Now, as familiar (or unfamiliar) as many may be about the different geographical terms
used here on Earth, replace your forests and rivers and lakes with craters and chasmata
and planitiae, and we begin to see some very different names used in these spheres.
Now this isn’t necessarily geography, since “geo” literally means Earth (like the
geocentric vs. heliocentric models), so what term would be more appropriate?
Well “geography” might be fine, but if we replace the “geo” with “astro”
we get astrography… which doesn’t help at all, since that actually refers to star
charts and things like that (i.e. how the stars are positioned, not the features of
the things orbiting said stars).
What about another term, planetology?
More often known as planetary science, planetology-- as we will call it for simplicity-- is a very
wide study encompassing studies of planets, moons, and planetary systems, with one field
being astrogeology, which is what Wiktionary uses to refer to these terms, so close enough.
Alright, let’s get down into the individual terms.
First, what the hell is a planitia?
In short, planitia derives from the word plain, and indeed a planitia (like the Utopia Planitia
on Mars, where the USS Enterprise-D was built) is a low-lying plain, also similar to a planum…
not exactly much more to that.
A chasma is also somewhat similar to a certain word it sounds like, chasm.
Except, a chasma actually refers to a steep-sided depression, similar to a valley, with one
notable example being the Ithaca Chasma on Saturn’s moon Tethys.
Shallow out the depressions though, and you get a fossa, a long, narrow, shallow-sided
depression, and in this case not a carnivorous mammal indigenous to Madagascar known for
eating lemurs (by the way, yes, fossa are indeed real).
Lastly in our list of plains and valleys is a vallis, which as I’m sure you can guess
by its name and its association with Mars’ Valles Marineris-- the largest valley in the
Solar System-- a vallis is… just that, a kind of valley.
Now there’s one very key-- and obvious-- difference between the Earth and the other
planets and moons of the Solar System: Earth is where we live, and everywhere else we look
at through telescopes.
What this means is that while you can’t really measure the population density of Ganymede,
how much light is reflected off a particular surface is indeed quite important in naming
astrogeological regions, a measurement which is known as albedo (something that would obviously
never apply to Earth geography).
So first in this category is an albedo feature, an indeed very broad measurement that can
refer to just about anything, as long as it looks exceptionally bright to a telescope,
in contrast to surrounding areas.
In this sense, a macula is kind of the opposite, being an “unusually” dark region of a
body, and a regio is an area differentiated by color or albedo (think Pluto’s Tombaugh
Regio).
Last among this crowd are terras, not to be confused with the name for Earth in pretty
much all of science fiction, a terra is a rough upland or a mountainous region, with
a high albedo.
So a crater happens when a body collides with another body, basically everyone knows that,
but when that happens multiple times in a long line, that results in a feature known
as a catena, best seen here with the Enki Catena on Ganymede.
A patera however is a crater that’s either irregular or with scalloped edges, and can
be formed by volcanoes instead of asteroids, though that’s not a requirement.
Speaking of well-known features on the Moon, you know how the Apollo 11 mission landed
in the Sea of Tranquility?
Well you do now, but since the Moon can’t support liquid water on its surface, its “seas”
are correctly known as maria, singular mare, which can mean different things on different
bodies, like a large, dark flatland on the Moon, a dark albedo area on Mars, or on Titan
an actual sea… just made of liquid methane.
Okay that’s enough talk about things dipping down into the surface, now let’s talk about
things jutting up out of the surface, the tallest of which on Earth is of course Mount
Everest, but in the Solar System it is Mars’ Olympus Mons.
A mons is just the word for a mountain, while a montes refers to a mountain range.
A mensa on Earth refers to an organization of people with a super-high IQ, but on other
worlds is flat-topped prominence with cliff-like edges, i.e. a mesa.
A tholus is a small, dome-shaped mountain, like the Hecates Tholus on Mars.
A dorsum refers to a ridge on a hill, an undae-- when used on Venus, Mars or Titan-- refers
to a field of dunes, and lastly a rupes is a kind of escarpment, which is itself like
the face of a cliff.
Now there are at least forty more terms I’m completely tossing out the window, but to
wrap this video up, I thought we’d also address how these features are named.
You can check out the Wikipedia page ‘Planetary nomenclature’ for the full list, but you
might have noticed some distinct themes with the names of these formations, mainly Greco-Roman
mythology, among others.
For instance, most features on Venus are mostly given feminine names, for example fossae are
named after goddesses of war, paterae are named after famous women, and planitiae are
named after mythological heroines.
On the Moon however, craters are named after dead scientists, artists and explorers, and
many features (including maria) are just named after Latin terms describing weather and abstract
concepts, like tranquility.
Finally on the moons of Pluto, having only recently been *mostly* mapped, they just said,
“you know what, screw it!
Kirk Crater, Vulcan Planum, Serenity Chasma, Ripley Crater, Kubrick Mons”.
So yeah, always nice to remember that NASA scientists are kind of just like everyone
else in a way…
although with that in mind, leave it up to the internet and we’d probably be seeing
“swag crater” and “heccin’-chonker mons”.
So that’s that, thanks for watching and let me know what you thought of this.
I have absolutely no idea how this video will do compared to my more culturally-oriented
videos, so please let me know, should I make more space videos (like I really want to)?
Should I not?
Should I make a poster of these different terms on my merch store (which does very much
exist)?
Either way, like, share, and subscribe to learn something new every Sunday.