Sand dunes on Mars are fascinating. They shift and move in different ways than they do on Earth, and they can grow to much more immense sizes than on our own planet. Several conditions contribute to the gigantic sand dunes and large fields of dunes that can form on the Red Planet, including its low gravity and air pressure.
Seasonal changes affect the Martian sand dunes, as well.
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.
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.
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.
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.
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.”
Titan is Saturn’s largest moon and is constantly surprising scientists as the Cassini spacecraft probes under its thick atmosphere. Take its dunes, for example, which are huge and pointed the wrong way.
Why are they pointing opposite to the prevailing east-west winds? It happens during two rare wind reversals during a single Saturn year (30 Earth years), investigators suggest.
Investigators repurposed an old NASA wind tunnel to simulate how Titan is at the surface, watching how the wind affects sand grains. (They aren’t sure what kind of sand is on Titan, so they tried 23 different kinds to best simulate what they think it is, which is small hydrocarbon particles that are about 1/3 the density of what you find on Earth.)
After two years of work with the model — not to mention six years of refurbishing the tunnel — the team determined that the wind must blow 50% faster than believed to get the sand moving.
“It was surprising that Titan had particles the size of grains of sand—we still don’t understand their source—and that it had winds strong enough to move them,” stated Devon Burr, an associate professor at the University of Tennessee Knoxville’s earth and planetary science department, who led the research. “Before seeing the images, we thought that the winds were likely too light to accomplish this movement.”
The winds reverse when the Sun moves over the equator, affecting Titan’s dense atmosphere. And the effects are powerful indeed, creating dunes that are hundreds of yards (or meters) high and stretch across hundreds of miles (or kilometers).
To accomplish this, the winds would need to blow no slower than 3.2 miles per hour (1.4 meters per second), which sounds slow until you consider how dense Titan’s atmosphere is — about 12 times thicker surface pressure than what you would find on Earth. More information on the research is available in the journal Nature.
Looking like the flowing designs carved by a Zen gardener’s rake, long parallel dunes of hydrocarbon sand stretch across the surface of Saturn’s moon Titan. The image above, acquired by Cassini in July 2013, reveals these intriguing and remarkably Earthlike landforms in unprecedented detail via radar, which can easily pierce through Titan’s thick clouds.
I’m feeling a little more enlightened already.
Although it piles into dunes like sand does here, Titan’s sand is not the same as what you’d find on a beach here on Earth. According to an ESA “Space in Images” article:
While our sand is composed of silicates, the ‘sand’ of these alien dunes is formed from grains of organic materials about the same size as particles of our beach sand. The small size and smoothness of these grains means that the flowing lines carved into the dunes show up as dark to the human eye.
Radar imaging, although capable of seeing through Titan’s opaque orange atmosphere, doesn’t capture visible-light images. Instead it’s sensitive to the varying textures of a landscape as they reflect microwaves; the smoother an object or an area is the darker it appears to radar, while irregular, rugged terrain shows up radar-bright.
The pixelated “seam” cutting horizontally across the center is the result of image artifacting.
In this image acquired on January 5, Cassini’s near-infrared vision pierced Titan’s opaque clouds to get a glimpse of the dark dune fields across a region called Senkyo.
The vast sea of dunes is composed of solid hydrocarbon particles that have precipitated out of Titan’s atmosphere. Also visible over Titan’s southern pole are the rising clouds of the recently-formed polar vortex.
For a closer look at Titan’s dunes (and to find out what the name Senkyo means) keep reading…
In the image above north on Titan is up and rotated 18 degrees to the right. It was taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers.
The view was obtained at a distance of approximately 750,000 miles (1.2 million kilometers) from Titan.
Titan’s hydrocarbon dunes are found across the moon in a wide swath within 30 degrees of the equator and are each about a kilometer wide and tens to hundreds of kilometers long… and in some cases stand over 100 meters tall. (Source: Astronomy Now.)
Observations of the dunes with Cassini and ESA’s Huygens probe during its descent onto Titan’s surface have shown that the moon experiences seasonally-shifting equatorial winds during equinoxes, similar to what occurs over the Indian Ocean between monsoon seasons.
The name Senkyo refers to the Japanese realm of serenity and freedom from wordly cares and death… in line with the IAU convention of naming albedo features on Titan after mythological enchanted places.
Click here for an earlier view of Senkyo, and follow the Cassini mission here.
Say the word “dunes” and the image that likely comes to mind is the sort of features you’d see in the Sahara Desert; huge mounds of carmel-colored shifting sand. But on Mars, dunes take on an entirely different connotation, and with the orbital eyes of the HiRISE camera on the Mars Reconnaissance Orbiter, we’ve seen some pretty bizarre-looking dunes. Take the image above for example, a newly released photo of well-speckled dunes in Mars’ north polar region. In this image, taken during the northern spring season, the dunes and ground are still covered in seasonal frost. “The speckled appearance is due to the warming of the area — as the carbon dioxide frost and ice on the dunes warms, small areas warm and sublimate (turn from solid to gas) faster, creating small jets that expose/deposit dark sand and dust onto the surface,” writes Serina Diniega on the HiRISE website. “Notice that there are no spots on the ground between the dunes — that is because the ground stays more uniformly cold, unlike the darker dune sand.”
See below for more weird dunes on Mars.
These dunes look as through someone has thrown a rippled blue-toned cloth across Mars’ surface. HiRISE is monitoring these dunes in Aonia Terra for changes such as gullies, which form over the winter from the action of carbon dioxide frost. This image was taken on January 18, 2012 here on Earth, but the season in on Mars where this was taken was late fall in the Southern hemisphere. “Frost is just starting to accumulate here, and is concentrated on pole-facing slopes and in the troughs between the meter-scale ripples,” wrote HiRISE Principal Investigator Alfred McEwen.
The benefit of long-term observations from orbit became evident today with the release of images from NASA’s Mars Reconnaissance Orbiter showing the subtly shifting motion of large sand dunes on the red planet, proving that the surface of Mars is much more dynamic than previously believed!
The atmosphere of Mars is extremely thin – only 1% as dense as Earth’s. This means that Martian winds would seem barely perceptible to a human, and has to blow at high speeds to move even the smallest particles on its surface.
Although scientists have known that Mars contains many dunes and vast expanses of sandy regions it has been assumed that these features must move very slowly – if at all – due to the thin air.
“We used to think of the sand on Mars as relatively immobile, so these new observations are changing our whole perspective.”
– Nathan Bridges, lead author
Now, images taken at different intervals by the MRO’s HiRISE camera have been seen to clearly show the shifting motion of several large sand dune features (called bedforms) in various locations on Mars.
“Mars either has more gusts of wind than we knew about before, or the winds are capable of transporting more sand,” said Nathan Bridges, planetary scientist at the Johns Hopkins University’s Applied Physics Laboratory and lead author of a paper published online in the journal Geology. “We used to think of the sand on Mars as relatively immobile, so these new observations are changing our whole perspective.”
Sandy particles on Earth that could be moved by a 10 mph breeze would require an 80 mph gust of Martian wind. Weather data and climate models have shown that such winds should be rare on Mars; these recent findings by MRO indicate that either high-speed winds are more common than once thought or else they are more capable of moving sand around… or a combination of both!
Not all of Mars’ dunes are so restless, though. The study showed that there are regions that show no movement.
“The sand dunes where we didn’t see movement today could have larger grains, or perhaps their surface layers are cemented together,” Bridges said. “These studies show the benefit of long-term monitoring at high resolution.”
Ten years ago the belief was that dunes on Mars are either static or move too slowly to detect. Thanks to MRO and the HiRISE team – and the authors of this new paper – we now know that idea is all just dust in the wind.
I just got lost on Mars. I saw this intriguing image, above, on the HiRISE camera website, and ended up spending a large chunk of my morning just wandering through the dunes of Mars — actually wandering through images of dunes on Mars. These striking features have to be one of the most intriguing areas of study on the Red Planet since they are one of the most dynamic geologic processes going on currently on Mars.
The dark dunes are composed of basaltic sand, and scientists believe the dunes in the image above have formed in response to fall and winter westerly winds. Also superimposed on their surface are smaller secondary dunes that are commonly seen on terrestrial dunes of this size.
See below for more intriguing dunes on Mars that I came across in my wanderings…
We’ve posted this image before, as it really is a weird-looking landscape, but it is worth seeing again.