Today I’ve got something different. Today NASA announced the discovery of hydrated salts in some dark slope features that form during the spring on Mars. These “recurring slope lineae”, or RSLs, were discovered a few years back, and they form on steep slopes every spring in a few places on Mars. There’s been a big debate over whether these things are formed by flowing water (which would be big news: flowing water on Mars today, right now, where we can witness and study it, not just billions of years ago in the distant past – these RSLs could be an environment where life could exist) or whether they’re just boring dry flows of sand or dust that only turn dark because for some weird reason the bright dust gets kicked off the surface (things like that also happen on Mars in other places).
But now they’ve found hydrated salts, which only form in the presence of water. So that means these RSLs are associated with water. They’re not just dry sandy avalanches. So now they’re places we need to pay more attention to, partly because we might find life there (yay!) and also because we need to be careful not to kill it or infect it with our biological cooties (boo!).
So in honor of this new discovery, I’m giving you a list of some of the words we’ve used to describe landforms on Mars. It’s true, we planetary scientists have a penchant for acronyms and names that don’t roll off the tongue. It may be partly because we lack imagination, but it’s also partly to cover ourselves (CYA, there’s another 3 letter acronym), so that we don’t pick a name that makes us assume something about what process forms that feature. Thus we have the mighty “recurring slope lineae” instead of something more catchy like “springtime slush”, because what if that name stuck and they turned out to be something much less exciting? Then we’d have to call them by the wrong name, and it would be the Pluto demotion fiasco all over again. Nobody wants that.
With some luck these RSLs will be renamed something more catchy. Most likely the IAU (another acronym!) will give them names relating to water features on Earth, like naming them after famous springs or fountains or something. That won’t happen for years to come. In the meantime, you can make your very own 3 letter acronym from the list above and play at martian geology. Have fun!
A Piece of Mars: In this 676×380 m (0.42×0.24 mi) scene, the high-standing hills here were all carved by sandblasting, by a wind that probably blew from right to left. Ripples in the valleys show that this erosion is still occurring today. (HiRISE ESP_041864_1745, NASA/JPL/Uni. of Arizona)
A piece of Mars: Not all sand piles up into big dunes. If the grains are the wrong grain size (too fine or too coarse), then it might just form sand sheets with ripples on top, like it does here, slowly migrating from top left to bottom right. There are two different kinds of sand here: the ripples seem more grayish and the underlying sand sheet seems more brownish. Grains of different sizes and densities respond to the wind in varying ways, so that they form different features on the surface. (HiRISE ESP_041977_1515, NASA/JPL/Univ. of Arizona)
A piece of Mars: On the left is high ground, covered with dunes (or maybe they’re ripples) running from upper left to lower right. On the right is low ground, covered in deeply eroded dunes (ripples?) running almost from left to right. They were probably created at two different times by winds that changed direction in the intervening time. The set on the right is probably much older. (HiRISE ESP_041991_1715, NASA/JPL/Univ. of Arizona)
A piece of Mars: These dunes look strangely triangular, a little bit like a flock of stealth bombers. Why? They’re two-faced barchans. Each flat face is an avalanche slope that faces downwind, formed by one of two distinct wind patterns that blow in this area (probably seasonally). Dunes like this can form on Earth, but the older slip face tends to be quickly erased as the winds change. (HiRISE ESP_027854_2150, NASA/JPL/Univ. of Arizona)
A piece of Mars: There’s an egg-shaped plateau here (the whole scene is 480×270 m or 525×295 yd across, the “egg” is ~100 m long). It’s partly covered by dunes that have extended across it. Or were the dunes there first and it buried them? Probably the former, but you can try to convince yourself either way. What do you think? (HiRISE ESP_041134_1720, NASA/JPL/Univ. of Arizona)
A piece of Mars: So much wind. There are dark swirly tracks of dust devils that have passed by, ripples covering dunes, wind scours around rocks, and of course dunes. Dune crests have a different color than other regions: are they less covered in dust? made of a more grayish sand that is more easily blown up the dune by the wind? or both? (HiRISE ESP_040885_1295, NASA/JPL/Univ. of Arizona)
A piece of Mars: In this image (0.96×0.54 km or 0.6×0.33 mi), it’s late winter and the sun is barely above the horizon here near the north pole. The dunes are covered in winter frost, most of which is CO2 ice (also known as dry ice). The dark regions are those facing the sun, where the ice has started to sublimate, revealing the dark sand below. (HiRISE ESP_041433_2650, NASA/JPL/Univ. of Arizona)
A piece of Mars: These dunes are some of the smallest on Mars. The smallest in this frame is ~150 m long (492 ft). But the smallest Earth dunes are ~20 m across. Why are they so much bigger on Mars? The air is thinner, so the wind has to blow stronger to lift sand grains. So once the sand is moving, it goes fast – and therefore goes farther before it lands. This makes for a bigger dune. (HiRISE ESP_41809_1890, NASA/JPL/Univ. of Arizona)
A piece of Mars: this 0.96×0.54 km (0.6×0.33 mi) scene shows a large, rippled dune that is slowly marching towards the upper right. The smooth striped band running from upper left to lower right is the slip face, where sand pushed by the wind eventually avalanches. Smaller scars show where slope failures (little landslides) have formed. (HiRISE ESP_027432_1350, NASA/JPL/Univ. of Arizona)