Mercury A to Z: Weird Terrain

Hello, friends!  We’re getting close to the end of this year’s A to Z Challenge, when the last few letters of the alphabet start forcing challenge participants to get weird.  My theme for this year’s challenge is the planet Mercury.  Fittingly, in today’s post, W is for:


Mountains, canyons, plateaus, glaciers, plains, hills, deserts… we already have names for these things.  But scientists sometimes discover landscapes on other worlds that we simply don’t have here on Earth, and they have to invent new words to describe them.  There’s the spider-like araneiform terrain on Mars, or the chaos terrain on Europa, or the cantaloupe terrain on Triton, which really does make parts of Triton look like the skin of a cantaloupe.  In 1974, scientists discovered a weird, new kind of terrain on Mercury.  They decided to call it weird terrain.

If you recall my post about Caloris Basin, then you know that just shy of four billion years ago a gigantic asteroid smashed into Mercury, giving Mercury a crater larger than the state of Texas.  Mercury’s weird terrain is on the exact opposite side of the planet.  This is almost certainly not a coincidence.

Three factors probably contributed to the formation of Mercury’s weird terrain.  Some people say that Mercury’s weird terrain looks almost like something tried to punch its way up through the planet’s crust, and that may be exactly what happened.  When that giant asteroid slammed into Mercury, the force of the impact went straight through the planet and ripped up the ground on the planet’s opposite side.

Additionally, the force of the impact would have sent tremendous seismic waves rippling through the planet’s crust.  When those seismic waves converged on the exact opposite side of the planet, they further disrupted the planet’s crust in that region.

And then there’s one more thing.  The impact event that created Caloris Basin would have sent debris flying all over the planet.  Clouds of flying debris probably converged on the opposite side of the planet.  When that happened, rocky debris started to rain down on that one badly disrupted patch of land.  That one patch of land would have looked weird enough already, so the extra rubble falling from above would have made it look even weirder.

Words like “jumbled” and “haphazard” are sometimes used to describe Mercury’s weird terrain.  In some images, the landscape reminds me a little of a stucco finish.  With the ground being ripped up from below and all that debris raining down from above, it’s little wonder that weird terrain looks the way it does. As far as I know, Mercury’s weird terrain is unique in the Solar System.  I feel like I could be wrong about that, though, so if anyone knows of something similar that’s happened anywhere else, I’d love to hear about it.


This article from the Planetary Society goes into a little more detail about how Mercury’s weird terrain was discovered and how it probably formed.

Mercury A to Z: Uplands

Hello, friends!  Welcome back to the A to Z Challenge.  For this year’s challenge, my theme is the planet Mercury, and in today’s post U is for:


Science Fiction

The year is 2059.  With the benefit of newly invented gravity manipulation technology, NASA has determined that they can safely and economically place a small rover on the surface of Mercury.  The first ever Mercury rover will land in a region just south of Mercury’s equator, part of the so-called “uplands” of Mercury.

Science Fact

There are generally two types of terrain on Mercury: the smoother, flatter volcanic plains regions, which are mostly found in the northern hemisphere, and the rougher, craggier, more heavily cratered “uplands,” which are found in Mercury’s equatorial regions and extend into the southern hemisphere.

Those smoother, flatter regions formed through a process planetary scientists call “resurfacing,” which is one of my favorite scientific euphemisms.  Resurfacing sounds like something you do to a parking lot.  What resurfacing actually means, in reference to planets, is that some sort of extreme volcanic activity covered part of a planet’s surface in lava.  The lava cooled and hardened, creating a smooth new surface and covering up whatever surface topography may have been present in the past.

Mercury is not a volcanically active world today, but it must have been at some point.  Most likely, the partial resurfacing of Mercury happened shortly after the end of the late heavy bombardment, a critical period in the history of our Solar System when the inner planets got pelted with asteroids.  Lava pooled in low elevation regions of Mercury, either filling in or totally covering up craters left by the late heavy bombardment.  But higher elevation regions—the uplands, in other words—were spared from resurfacing.

Similar upland terrain can be found on the Moon, and studying the lunar uplands has told scientists much about what the Solar System was like during the late heavy bombardment.  Comparing and contrasting the uplands of the Moon with the uplands of Mercury may give us an even clearer and more detailed picture of what that era of the Solar System’s history was like.  For this reason, a mission to explore the uplands of Mercury could be very interesting and exciting for scientists.

Science Fiction

NASA apparently failed to learn their lesson after the public naming contest for their mission to Uranus and proceeded to hold another public naming contest for the Mercury Uplands Rover.  And that is how NASA’s Up-Dog Mission officially came to be.


Here is a 2016 article from NASA announcing the first complete topographic map of the surface of Mercury.

And here is an article from about the Moon and Mercury and the things we might learn by comparing and contrasting the two.

P.S.: If you don’t understand the up-dog reference, feel free to ask me “What is up-dog?” in the comments below.

Sciency Words: Europa Edition

Hello, friends, and welcome back to Sciency Words!  That’s right, Sciency Words is back!  I’m going to handle this series a little differently than I did before.  I could explain what those differences are, but I think it’s better if we just dive right in so you can see for yourselves.

Since this is officially Europa Month here on Planet Pailly, we’re going to turn our attention to Europa, the sixth moon of Jupiter.  When exploring alien worlds, scientists sometimes discover geological features that are not found here on Earth.  When that happens, scientists need to invent new words to describe what they’re seeing.  Here are a few of the terms used to describe geological surface features seen on Europa.

Chaos Terrain: For the most part, Europa’s surface is made of very smooth, very fresh-looking ice.  But in some regions, we find these big, broken chunks of ice in a state of chaotic disarray.  Imagine a bunch of icebergs breaking loose from a glacier.  Now imagine that, before the icebergs drift too far, the water around them freezes, locking those icebergs in place.  That’s basically what chaos terrain looks like.  Oh, and chaos terrain tends to be discolored with some sort of reddish-brown substance.  Click here to see some chaos terrain on Europa.

Linea (plural, lineae): From the Latin word for line, linea means… line.  Reddish-brown lineae crisscross the surface of Europa.  They appear to be cracks in Europa’s icy surface, cracks which have been filled in by a mixture of freshly frozen ice and more of that reddish-brown substance.  Click here to see a color enhanced view of Europa’s lineae.

Lenticula (plural, lenticulae): From the Latin word for freckles, lenticulae are small, reddish-brown spots scattered all over the surface of Europa.  They tend to be round, but they don’t appear to be impact craters, which means they’re probably caused by something happening beneath Europa’s surface.  Click here to see a cluster of lenticulae on Europa’s surface.

Macula (plural, maculae): From the Latin word for spot, maculae are spots of discoloration on the surface of a planet or moon.  Europa’s maculae are irregularly shaped blotches of reddish-brown color.  At least one macula (known as Thera Macula) has been identified as a possible region of active chaos terrain formation.  Click here for a closer look at Thera Macula.

It’s extremely cold in the outer Solar System, so cold that water behaves almost like a kind of rock.  When thinking about icy worlds like Europa, it can be helpful to conceptualize water in that way.  Water is a kind of rock.  With that in mind, Europa’s icy surface is much like the rocky crust we have here on Earth, and Europa’s subsurface ocean of liquid water is sort of like the layer of molten rock that lies beneath Earth’s crust.  And thus the surface features we see on Europa might be caused by processes similar to the tectonic and volcanic activity we experience here on Earth.

There are, of course, other geological terms associated with Europa, but for this post I wanted to focus on just these four.  Europa’s chaos terrain, lineae, lenticulae, and maculae all have something important in common: that reddish-brown discoloration.  Next time on Planet Pailly, we’ll try to figure out what, exactly, that reddish-brown stuff on Europa is.