These Streaks on Mars Could be Flowing Sand, not Water

When robotic missions first began to land on the surface of Mars in the 1970s, they revealed a harsh, cold and desiccated landscape. This effectively put an end generations of speculation about “Martian canals” and the possibility of life on Mars. But as our efforts to explore the Red Planet have continued, scientists have found ample evidence that the planet once had flowing water on its surface.

In addition, scientists have been encouraged by the appearance of Recurring Slope Lineae (RSL), which were believed to be signs of seasonal water flows. Unfortunately, a new study by researchers from the U.S. Geological Survey indicates that these features may be the result of dry, granular flows. These findings are another indication that the environment could be too dry for microorganisms to survive.

The study, titled “Granular Flows at Recurring Slope Lineae on Mars Indicate a Limited Role for Liquid Water“, recently appeared in the scientific journal Nature Geoscience. Led by Dr. Colin Dundas, of the US Geological Survey’s Astrogeology Science Center, the team also included members from the Lunar and Planetary Laboratory (LPL) at the University of Arizona and Durham University.

This inner slope of a Martian crater has several of the seasonal dark streaks called “recurrent slope lineae,” or RSL, which were caputred by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter. Credits: NASA/JPL-Caltech/UA/USGS

For the sake of their study, the team consulted data from the High Resolution Image Science Experiment (HiRISE) camera aboard the NASA Mars Reconnaissance Orbiter (MRO). This same instrument was responsible for the 2011 discovery of RSL, which were found in the middle latitudes of Mars’ southern hemisphere. These features were also observed to appear on Martian slopes during late spring through summer and then fade away in winter.

The seasonal nature of these flows was seen as a strong indication that they were the result of flowing salt-water, which was indicated by the detection of hydrated salt at the sites. However, after re-examining the HiRISE data, Dundas and his team concluded that RSLs only occur on slopes that are steep enough for dry grains to descend – in much the same way that they would on the faces of active dunes.

As Dundas explained in a recent NASA press release:

“We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand. This new understanding of RSL supports other evidence that shows that Mars today is very dry.”

Using pairs of images from HiRISE, Dundas and his colleagues constructed a series of 3-D models of slope steepness. These models incorporated 151 RSL features identified by the MRO at 10 different sites. In almost all cases, they found that the RSL were restricted to slopes that were steeper than 27° and each flow ended on a slope that matched the patterns seen in slumping dry sand dunes on Mars and Earth.

Dark, narrow streaks flowing downhill on Mars at sites like the Horowitz Crater are inferred to be due to seasonal flows of water. Credit: NASA/JPL-Caltech/Univ. of Arizona

Basically, sand flows end where a steep angle gives way to a less-steep “angle of repose”, whereas liquid water flows are known to extend along less steep slopes. As Alfred McEwen, HiRISE’s Principal Investigator at the University of Arizona and a co-author of the study, indicated, “The RSL don’t flow onto shallower slopes, and the lengths of these are so closely correlated with the dynamic angle of repose, it can’t be a coincidence.”

These observations is something of a letdown, since the presence of liquid water in Mars’ equatorial region was seen as a possible indication of microbial life. However, compared to seasonal brine flows, the present of granular flows is a far better fit with what is known of Mars’ modern environment. Given that Mars’ atmosphere is very thin and cold, it was difficult to ascertain how liquid water could survive on its surface.

Nevertheless, these latest findings do not resolve all of the mystery surrounding RSLs. For example, there remains the question of how exactly these numerous flows begin and gradually grow, not to mention their seasonal appearance and the way they rapidly fade when inactive. On top of that, there is the matter of hydrated salts, which have been confirmed to contain traces of water.

To this, the authors of the study offer some possible explanations. For example, they indicate that salts can become hydrated by pulling water vapor from the atmosphere, which might explain why patches along the slopes experience changes in color. They also suggest that seasonal changes in hydration might result in some trigger mechanism for RSL grainflows, where water is absorbed and release, causing the slope to collapse.

NASA’s Mars Reconnaissance Orbiter investigating Martian water cycle. Credit: NASA/JPL/Corby Waste

If atmospheric water vapor is a trigger, then it raises another important question – i.e. why do RSLs appear on some slopes and not others? As Alfred McEwen – HiRISE’s Principal Investigator and a co-author on the study – explained, this could indicate that RSLs on Mars and the mechanisms behind their formation may not be entirely similar to what we see here on Earth.

“RSL probably form by some mechanism that is unique to the environment of Mars,” he said, “so they represent an opportunity to learn about how Mars behaves, which is important for future surface exploration.” Rich Zurek, the MRO Project Scientist of NASA’s Jet Propulsion Laboratory, agrees. As he explained,

“Full understanding of RSL is likely to depend upon on-site investigation of these features. While the new report suggests that RSL are not wet enough to favor microbial life, it is likely that on-site investigation of these sites will still require special procedures to guard against introducing microbes from Earth, at least until they are definitively characterized. In particular, a full explanation of how these enigmatic features darken and fade still eludes us. Remote sensing at different times of day could provide important clues.”

In the coming years, NASA plans to carry out the exploration of several sites on the Martian surface using the Mars 2020 rover, which includes a planned sample-return mission. These samples, after being collected and stored by the rover, are expected to be retrieved by a crewed mission mounted sometime in the 2030s, and then returned to Earth for analysis.

The days when we are finally able to study the Mars’ modern environment up close are fast approaching, and is expected to reveal some pretty Earth-shattering things!

Further Reading: NASA

What Made this Mysterious Pit on Mars? Impact Crater or Natural Collapse?

The HiRISE camera on NASA's Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique "Swiss cheese" like appearance. Image:NASA/JPL/University of Arizona
The HiRISE camera on NASA's Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique "Swiss cheese" like appearance. Image:NASA/JPL/University of Arizona
The HiRISE camera on NASA’s Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique “Swiss cheese” like appearance. Image:NASA/JPL/University of Arizona

During late summer in the Southern hemisphere on Mars, the angle of the sunlight as it strikes the surface brings out some subtle details on the planet’s surface.

In this image, the HiRISE camera on board NASA’s Mars Reconnaissance Orbiter (MRO) captured an area of frozen carbon dioxide on the surface. Some of the carbon dioxide ice has melted, giving it a swiss-cheese appearance. But there is also an unusual hole or crater on the right side of the image, with some of the carbon dioxide ice clearly visible in the bottom of the pit.

NASA scientists are uncertain what exactly caused the unusual pit. It could be an impact crater, or it could be a collapsed pit caused by melting or sublimation of sub-surface carbon dioxide ice.

MRO has been in orbit around Mars for over 10 years, and has completed over 50,000 orbits. The MRO has two cameras. The CTX camera is lower resolution, and has imaged over 99% of the Martian surface. HiRISE is the high-resolution camera that is used to closely examine areas and objects of interest, like the unusual surface pit in this image.

More Reading:

Ever Wondered What Final Approach To Mars Might Feel Like?

We’ve posted several ‘flyover’ videos of Mars that use data from spacecraft. But this video might be the most spectacular and realistic. Created by filmmaker Jan Fröjdman from Finland, “A Fictive Flight Above Real Mars” uses actual data from the venerable HiRISE camera on board the Mars Reconnaissance Orbiter, and takes you on a 3-D tour over steep cliffs, high buttes, amazing craters, polygons and other remarkable land forms. But Fröjdman also adds a few features reminiscent of the landing videos taken by the Apollo astronauts. Complete with crosshatches and thruster firings, this video puts you on final approach to land on (and then take off from) Mars’ surface.

(Hit ‘fullscreen’ for the best viewing)

To create the video, Fröjdman used 3-D anaglyph images from HiRISE (High Resolution Science Imaging Experiment), which contain information about the topography of Mars surface and then processed the images into panning video clips.

Fröjdman told Universe Today he worked on this video for about three months.

“The most time consuming was to manually pick the more than 33,000 reference points in the anaglyph images,” he said via email. “Now when I count how many steps there were in total in the process, I come to seven and I needed at least 6 different kinds of software.”

A new impact crater that was formed between July 2010 and May 2012, as seen by the HiRISE camera on the Mars Reconnaissance Orbiter. This image is part of “A Fictive Flight Above Real Mars” by Jan Fröjdman. Credit: NASA/JPL/University of Arizona.

Fröjdman, a landscape photographer and audiovisual expert, said he wanted to create a video that gives you the feeling “that you are flying above Mars looking down watching interesting locations on the planet,” he wrote on Vimeo. “And there are really great places on Mars! I would love to see images taken by a landscape photographer on Mars, especially from the polar regions. But I’m afraid I won’t see that kind of images during my lifetime.”

Between HiRISE and the Curiosity rover images, we have the next best thing to a human on Mars. But maybe one day…

Fröjdman has previously posted other space-related videos, including video and images of the Transit of Venus in 2012 he took from an airplane, and a lunar eclipse in 2011.

A FICTIVE FLIGHT ABOVE REAL MARS from Jan Fröjdman on Vimeo.

Wow, Mars Sure Can Be Pretty

For a supposedly dead world, Mars sure provides a lot of eye candy. The High Resolution Imaging Science Experiment (HiRise) aboard NASA’s Mars Reconnaissance Orbiter (MRO) is our candy store for stunning images of Mars. Recently, HiRise gave us this stunning image (above) of colorful, layered bedrock on the surface of Mars. Notice the dunes in the center. The colors are enhanced, which makes the images more useful scientifically, but it’s still amazing.

HiRise has done it before, of course. It’s keen vision has fed us a steady stream of downright jaw-dropping images of Elon Musk’s favorite planet. Check out this image of Gale Crater taken by HiRise to celebrate its 10 year anniversary orbiting Mars. This image was captured in March 2016.

HiRise captured this image of unusual textures on the floor of the Gale Crater, the same crater where the Curiosity rover is working. Image: NASA/JPL-Caltech/Univ. of Arizona

The MRO is approaching its 11 year anniversary around Mars. It has completed over 45,000 orbits and has taken over 216,000 images. The next image is of a fresh impact crater on the Martian surface that struck the planet sometime between July 2010 and May 2012. The impact was in a dusty area, and in this color-enhanced image the fresh crater looks blue because the impact removed the red dust.

This color-enhanced image of a fresh Martian crater was captured by the HiRise camera. Image: NASA/JPL-Caltech/Univ. of Arizona

These landforms on the surface of Mars are still a bit of a mystery. It’s possible that they formed in the presence of an ancient Martian ocean, or perhaps glaciers. Whatever the case, they are mesmerizing to look at.

These odd ridges are still a mystery. Were they formed by glaciers? Oceans? Image: NASA/JPL-Caltech/Univ. of Arizona

Many images of the Martian surface have confounded scientists, and some of them still do. But some, though they look puzzling and difficult to explain, have more prosaic explanations. The image below is a large area of intersecting sand dunes.

What is this? A vast area of Martian rice paddies? Lizard skin? Nope, just an area of intersecting sand dunes. Image: NASA/JPL-Caltech/Univ. of Arizona

The surface of Mars is peppered with craters, and HiRise has imaged many of them. This double crater was caused by a meteorite that split in two before hitting the surface.

This double impact crater was caused by a meteorite that split into two before hitting Mars. Notice how the eroding force of the wind has shaped each crater the same, smoothing one edge and creating dunes in the same place. Image: NASA/JPL-Caltech/Univ. of Arizona

The image below shows gullies and dunes at the Russell Crater. In this image, the field of dunes is about 30 km long. This image was taken during the southern winter, when the carbon dioxide is frozen. You can see the frozen CO2 as white on the shaded side of the ridges. Scientists think that the gullies are formed when the CO2 melts in the summer.

These gullies are on the dunes of Russell Crater on Mars. This image was taken during winter, and the frozen carbon dioxide on the shaded slopes. Credit: NASA/JPL/University of Arizona

The next image is also the Russell Crater. It’s an area of study for the HiRise team, which means more Russell eye candy for us. This images shows the dunes, CO2 frost, and dust devil tracks that punctuate the area.

This image of the Russell Crater, an area of study for HiRise, shows the area covered in dunes, with some frost visible in the lower left. The larger, darker markings are dust devil tracks. Image: By NASA/JPL/University of Arizona – HiRISE, Public Domain,

One of the main geological features on Mars is the Valles Marineris, the massive canyon system that dwarfs the Grand Canyon here on Earth. HiRise captured this image of delicate dune features inside Valles Marineris.

These delicate dune features formed inside the Valles Mariners, the massive canyon system on Mars. Image: NASA/JPL/University of Arizona

The Mars Reconnaissance Orbiter is still going strong. In fact, it continues to act as a communications relay for surface rovers. The HiRise camera is along for the ride, and if the past is any indication, it will continue to provide astounding images of Mars.

And we can’t seem to get enough of them.

A Region On Mars With Recent Water Is About To Get Major Attention

Striations exposed on the surface between Martian sand dunes (one pictured at top) in Lucaya Crater indicate fluctuating levels of salty groundwater. At “a” we see possible cross beds which are tilted layers of sand within larger layers deposited by wind or water. At b, dark and light strata are similar to that exposed in the dune at top and resemble the striations seen in the Namib Desert on Earth. The photo was taken by NASA’s Mars Reconnaissance Orbiter in infrared, red and blue light. Credit: NASA/JPL-Caltech

Researcher Dr. Mary Bourke from Trinity College Dublin have discovered a patch of land in an ancient valley in Mars’ Lucaya Crater that appears to have held water in the not-too-distant past, making it a prime target to search for past life forms on the Red Planet. Signs of water past and present pop up everywhere on Mars from now-dry, wriggly riverbeds snaking across arid plains to water ice exposed at the poles during the Martian summer.

A valley lined with sand dunes crosses the southern floor of the 21-mile-wide Lucaya Crater, located at latitude 11° south and longitude 52° east on Mars. Striations found between the dunes may have been created by recent water flows. The box shows the area pictured in the close up above. The 3.7-mile-long valley measures between 2,000 and 2,600 feet wide. Credit: NASA/JPL-Caltech with additions by the author

On Earth, Bourke had done previous studies of dunes in the Namib Desert near Walvis Bay, Namibia and noted “arctuate striations” — crusty arcs of sand cemented by water and minerals — on the surfaces of migrating sand dunes using photos taken by satellite. She subsequently assembled a team to check them out on the ground and discovered that the striations resulted when dune materials had been chemically cemented by salts left behind by evaporating groundwater.

“On Earth, desert dune fields are periodically flooded by water in areas of fluctuating groundwater, and where lakes, rivers and coasts are found in proximity,” said Bourke. These periodic floods leave tell-tale patterns behind them.” Once the material had been cemented, it hardens and remains behind as the dunes continue to migrate downwind.

Compare these cemented arctuate striations between dunes near Walvis Bay, Namibia with those in Lucaya Crater’s valley in the earlier image. White arrows highlight particularly prominent examples. Photos in (b) and (c) were taken from the ground. The excavated pit in (c) shows that the dipping sediment layers below the surface match the protruding layers on the surface. Alternating light and dark layers have different salt composition and grain size. Credit: Google Earth (left) and Dr Mary Bourke, Trinity College Dublin

Next, Bourke and colleague Prof. Heather Viles, from the University of Oxford, examined close up images of Mars taken with the Mars Reconnaissance Orbiter (MRO) and experienced a flash of insight: “You can imagine our excitement when we scanned satellite images of an area on Mars and saw this same patterned calling card, suggesting that water had been present in the relatively recent past.”

Bourke examined similar arcuate striations exposed on the surface between dunes, indications of fluctuating levels of salty groundwater during a time when dunes were actively migrating down the valley.

A possible scenario: an asteroid impacts Mars, forming Lucaya Crater and unleashing water flows that created the crater valley and striations.

So where did the water come from to create the striations in the crater valley? Bourke and Viles propose that water may have been released by the impact that formed Lucaya Crater especially if the target area was rich in ice.

Extreme temperatures during the impact would have vaporized water but also possibly melted other ice to flow for a time as liquid water. Alternatively, the impact may have jump-started hydrothermal activity as hot springs-style underground flows.

Flowing water would have created the valley and saturated the soils there with salty water. In dry periods, erosion from the wind would have picked away the water-eroded sands to create the striking pattern of repeating dunes we see to this day.

Water, water everywhere … once upon a time. Nanedi Valles, a roughly 500-mile-long (800 km) valley extending southwest-northeast and photographed by Mars Express. In this view, Nanedi Valles ranges from approximately 0.5 – 3 miles (0.8- to 5.0 km) wide and extends to a maximum of about 1,640 feet (500 meters) below the surrounding plains. The valley’s origins remain unclear, with scientists debating whether erosion caused by ground-water outflow, flow of liquid beneath an ice cover or collapse of the surface in association with liquid flow is responsible. In all cases, it’s clear that water was involved. Copyright ESA/DLR/FU Berlin (G. Neukum)

Carbonate rocks, which require liquid water to form are dissolved by the same, have been detected in the valley using spectroscopy and could have served as the cement to solidify sands between the moving dunes. That in concert with alternating dry and wet periods would create the striations seen in the MRO photos.

“These findings are hugely significant,” said Bourke. “Firstly, the Martian sand dunes show evidence that water may have been active near Mars’ equator — potentially in the not-too-distant past. And secondly, this location is now a potential geological target for detecting past life forms on the Red Planet, which is important to those involved in selecting sites for future missions.”

Get Away From It All with these Amazing DTM Views of Mars

By day, Kevin Gill is a software engineer at the Jet Propulsion Laboratory. But on nights and weekends he takes data from spacecraft and turns them into scenes that can transport you directly to the surface of Mars.

Gill is one of many so-called “amateur” image editing enthusiasts that take real, high-resolution data from spacecraft and create views that can make you feel like you are standing on the surface of Mars, or out flying around the Solar System.

Gasa Crater on Mars. Rendered using Autodesk Maya and Adobe Photoshop. HiRISE data processed using HiView and gdal. Credit: NASA/JPL/University of Arizona/USGS/image editing by Kevin Gill.

Some of the best data around for these purposes come from the HiRISE camera on board the Mars Reconnaissance Orbiter. Data known as Digital Terrain Model (DTM) files, the HiRISE DTMs are made from two or more images of the same area of a region on Mars, taken from different angles. This data isn’t just for making stunning images or amazing movies. For scientists, DTMs are very powerful research tools, used to take measurements such a elevation information and model geological processes.

So, just how do you go from this DTM image from HiRISE:

DTM image of the Central Peak of Elorza Crater on Mars. Credit: NASA/JPL/University of Arizona/USGS

To this amazing image?

Martian sunrise over the Central Peak of Elorza Crater. Rendered using Autodesk Maya and Adobe Photoshop. HiRISE data processed using HiView and gdal. Credit: NASA/JPL/University of Arizona/USGS/image editing by Kevin Gill

I’m going to let Kevin explain it:

To prep the data, I use Photoshop (to convert the JP2 file to a TIFF), and then standard GIS tools like gdal (Geospatial Data Abstraction Library) to create textures for 3D modeling. Using Autodesk Maya, I input those into a material as a color texture (orthoimagery) or displacement map (the DTM data).

I connect that material to a NURBS plane (sort of like a polygon mesh) that is scaled similarly to the physical properties of the data. I set up a camera at a nice angle (it takes a number of low-resolution test renders to get an angle I like) and let it render.

Then I just pull that render into Photoshop where I have a series of monochromatic color tints which gives the image it’s Martian feel. For the sky, I use either a sky from a MSL MastCam image or one that I took outside with my cell phone. If I’m using a sky I took with my cell phone, I’ll adjust the colors to make it look more like it would on Mars. If the colors in the image are still boring at this point, I may run a HDR adjustment on it in Photoshop.

Fissure in the Cerberus region. This false color view of a volcanic fissure in the Cerberus region of Mars was created using a digital terrain model (DTM) from the High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA’s Mars Reconnaissance Orbiter. The horizon was taken from Curiosity Mastcam imagery. Credit: NASA/JPL-Caltech/University of Arizona/ image editing by Kevin Gill.

What all this means is that you can create all these amazing view, plus incredible flyover videos, like this one Kevin put together of Endeavour Crater:

Or you can have some fun and visualize where the Curiosity rover is sitting:

Doin’ Science with Curiosity. Created using HiRIST DTM and Ortho data and NASA model of Curiosity. Rendered using Autodesk Maya and Adobe Photoshop. Curiosity Model: Brian Kumanchik, NASA/JPL-Caltech. Image editing by Kevin Gill.

We’ve written about this type of image editing previously, with the work of the people at and others. Of course, the image editing software keeps improving, along with all the techniques.

Kevin also wanted to point out the work of other image editing enthusiast, Sean Doran.

“Sean’s work is resulting in views similar to mine,” Kevin said via email. “I know he’s using a process very different from mine, but we are thinking along the same lines in what we want out of the end product. His are quite impressive.”

For example, here is a flyover video of the Opportunity rover sitting along the rim of Endeavour Crater:

You can see more of Sean’s work on his Flickr page

And you can see all of Kevin’s Mars DTM images at his Flick page here. Kevin also recently wrote up a great explanation of his image editing for The Planetary Society, which you can read here.

Thanks to Kevin Gill for sharing his images and expertise!