It’s been a while since I’ve posted a jaw-dropping high-res picture from Mars, so how about this one: a gorgeous shot of frost coating dunes on the surface of the Red Planet?
[Oh yes, you want to click that to enaresenate.]
This picture was taken by the HiRISE camera on board the Mars Reconnaissance Orbiter, which takes extremely detailed images of the surface of the planet. It shows wind-driven sand dunes on Mars, rippling in a similar way as on Earth. The sunlight is coming from the upper left direction, and where the light hits the surface you can see the familiar reddish cast; that’s actually from very fine-grain dust laden with iron oxide — rust!
But the shadows, where the Sun doesn’t reach, it’s cold enough that carbon dioxide in the Martian air freezes out, forming a thin layer of dry ice on the surface. In this image — where the colors have been enhanced so you can see the effects better — this shades the dunes blue. You can see the frost not just covering the dunes in general, but hiding in the troughs of the ripples too (which I think is why the sunward facing parts of the dunes can look blue; that’s from the ripple shadows). The non-color-enhanced version showing the entire dune region can be found here — and is stunning in its own right.
These dunes fascinate me. The sand on Mars is actually basaltic, making it look grey to the eye. Those grains are big enough that they don’t move as easily as the finer dust, and they pile up to form the big dunes, with the redder dust coating them. The color can change when frost forms, as in the picture above, but you also get incredibly dramatic and simply stunning patterns when dust devils — tornado-like vortices that form when wind blows over warm air rising off the surface — lift up the red dust and expose the grey basalt underneath. The swirling patterns are intricate and incredible, as you can see in this picture here (click to embiggen and get more details).
Pictures like this remind me viscerally that these objects we see in the sky are not just some distant lights, they are whole worlds. They have fantastic details and are as diverse and have complex interactive systems as any we find on Earth. This makes their study important, fascinating… and of course, astonishingly beautiful.
Image credit: NASA/JPL/University of Arizona. Tip o’ the heat shield to HiRISE on Twitter.
Check. This. Out: a perfectly-formed collapse pit on Mars that leads to an underground cavern!
Amazing! [Click to barsoomenate.]
This was taken by the Mars Reconnaissance Orbiter in July 2011. See the hole in the bottom? You can tell from the lighting that this is an underground opening to a cavern — a skylight. Quite a few of these have been found on Mars, actually. We see them on Earth and even on the Moon. Given the angle of the shadows, the vertical distance from the bottom of the pit to the floor of the cavern is about 20 meters (65 feet). Watch your step!
Here’s how we think skylights like this form. In the distant past, Mars was geologically active. Rivers of lava ran across the surface. If the surface of the lava hardens it can form a roof, allowing the lava underneath to continue flowing; these are called lava tubes and there are bazillions of them in Hawaii, for example. Eventually, the source of the lava chokes off and the lava flows away, leaving the empty tube underground. If the roof is thin in one spot it can collapse. Sometimes that just leaves a hole, but apparently in this case it was under a sand field. Some of the sand must have fallen into the chamber below and eventually blown away, leaving the pit and the hole. The pit is located not too far from Pavonis Mons, a known (long-dead) Martian volcano.
The hole is about 35 meters (115 feet) across, so the pit is about 175 meters (nearly 600 feet) across the rim. I love how it sits in an otherwise nearly featureless sand field; the contrast is beautiful. In the high-res image you can see boulders perched on the pit wall, having rolled part of the way down as well. The inside of the pit has lines and furrows that are instantly recognizable to anyone who has tried to dig a hole at the beach and had sand continually flow down from the rim.
It would be incredible to see something like this up close. It’s possible eventually someone will: such lava tubes would make good homes for future Mars explorers; they’d be protected from sand storms, temperature swings, and solar radiation (which is worse than for us on Earth because Mars doesn’t have a strong magnetic field to protect it).
… but you couldn’t pay me enough to go inside one of those. I have no desire to be slowly digested over ten thousand years.
Image credit: NASA/JPL/University of Arizona. Tip o’ the light saber to reddit.
For the past few years, tantalizing evidence has been found that Mars — thought to be long dead, dry, and lifeless — may have pockets of water just beneath the surface. To be clear, we know there’s water on Mars, in the form of ice. We see ice in the polar caps, and we’ve seen it revealed under the surface by small meteorite impacts.
The question is, is there liquid water?
New images by the Mars Reconnaissance Orbiter bring us a step closer to answering that question. A series of pictures of the 300 km (180 mile) wide Newton crater taken over the course of several years show dark deposits on the crater wall which change predictably with the seasons, clearly affiliated with some sort of material flowing downslope:
[Click to barsoomenate.]
The picture above shows Newton’s crater wall. It’s pretty steep, with about a 35° slope, and the dark deposits are labeled. This crater is located in the southern mid-latitudes of Mars, and this part of the crater faces north. That’s critical! Since it faces toward the equator, that means it’s facing the Sun in the summer, and so these deposits appear when the temperatures get warm.
NASA has created several animated gifs (too big to embed here) that show the growth and retreat of these features over time. You can easily see how these dark features change.
In the past, similar things have been seen in gullies on Mars. It’s not clear those are from water, since frozen carbon dioxide can also be thawing out and forming them. In those cases, the flows were seen on the cold-facing sides of crater walls, making it less likely they’re from water. These new formations are on the warm-facing side, making it more likely they are from water.
So what’s going on? Read More
Sometimes, I see an image and do a double-take. This picture sure caused one:
[Click to barsoomenate.]
If I told you those were bacteria under a microscope, you might believe me for a minute or two. But actually, those are sand dunes on Mars!
Yup. It’s funny how bizarre and alien Mars can be. What you’re seeing in this image from the Mars Reconnaissance Orbiter HiRISE camera is actually two different kinds of sand: the dark stuff in the big dunes is actually made of grains of gray basaltic sand. They’re heavy and pile up into dunes. The ripply pinkish stuff between the dunes is made of smaller grains of sand laden with iron oxide — rust! The wind can shape those grains more easily, so they can form more gentle, smaller wavelike patterns. This is also why dust devils on Mars leave such amazing and intricate patterns.
Still, those dunes really look like microbes… and hey, wait a second. There are a set of characteristics that living things share: the ability to consume, excrete, multiply, and show complexity. Sand dunes consume, in a way: the wind brings in more sand to build them up. The excrete, too, by losing sand. They can grow, and split in half, making more. And in point of fact, they do show emergent complex behavior.
Maybe the dunes share more than just appearances with bacteria…could sand dunes actually be [dun dun dunnnnnn] alive*?