Tag: geology

The soft landslides of Mars

12:14 pm

A soft avalanche on Mars

Context image of landslide

The light gravity of Mars, combined with different materials, a lot of dust, and a geological history different from Earth, produces events that — though reminiscent of similar geological events on Earth — are definitely not the same.

The image above, cropped and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and was one of the many uncaptioned images released in the November archive. If you click on the image you can see the full resolution version. It shows the tongue of a landslide inside a crater located in the planet’s southern highlands.

You can immediately see why I call it a soft landslide. The craters on its top are barely visible, as if they hit a soft surface that absorbed most of the impact. The grooves spreading southward in the slide suggest that this solid material flowed almost like mud. And the soft, smooth surface head of the slide suggests an almost liquid-like flow. As far as I can tell, this landslide had few large boulders. It was made up instead of small particles of about the same size.

To the right is an image showing the wider context of the above image, taken by Mars Odyssey and cropped and annotated by me to post here. The white box shows the entire area photographed by the full resolution image of the landslide, with the tongue of the landslide at the bottom of the box. If you look at the floor of this crater, you can see what looks like the ghost of a past smaller impact, seemingly buried in either a field of lava or soft dusty regolith. The smoothness of the crater floor also suggests a material softness, allowing it to settle into a pondlike featureless flat plain.
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The fractured floor of Komarov Crater

10:35 am

Fractured floor of Komarov Crater

Cool image time! The Lunar Reconnaissance Orbiter (LRO) oblique image on the right, reduced significantly from the original to post here, shows the deeply fractured floor of Komarov Crater on the Moon’s far side. As noted at the image link,

The spectacular fractures that cut across the floor of Komarov crater [about 85 kilometers or 50 miles diameter] were formed when magma rose from the mantle, uplifting and fracturing the crater in the process. In this case the magma did not erupt to the surface, thus the fractures remain visible.

The Komarov fractures are quite large, the major left-to-right fracture that cuts across the center of the scene is over 500 meters deep [1,600 feet] and 2500 meters wide [1.5 miles]. When did they form? The large number of craters superimposed on the floor and fractures testifies to their ancient ages. Likely they are of the same vintage (>2.6 billion years) as the Mare Moscoviense lava plains just to the north

An overview of Komarov Crater as well as other LRO images of it can be found here.

The question that comes to my mind is the relative rarity of craters with such large fractures on their floors. I have noted this for Mars as well. It is expected that there is melt on the floor of all large impact craters. Why do a few produce such pronounced fractures, while most do not? This website posits one explanation, but its complexity leaves me unsatisfied. It also doesn’t explain why it happens only rarely.

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Scientists discover giant impact crater buried under Greenland ice

2:34 pm

Scientists have discovered the existence of a giant impact crater buried under the Greenland ice.

An international team of researchers, including a NASA glaciologist, has discovered a large meteorite impact crater hiding beneath more than a half-mile of ice in northwest Greenland. The crater — the first of any size found under the Greenland ice sheet — is one of the 25 largest impact craters on Earth, measuring roughly 1,000 feet deep and more than 19 miles in diameter, an area slightly larger than that inside Washington’s Capital Beltway.

They think, based on the data, that this crater is very young, one of the youngest known on Earth. At the most is is no more than 3 million years old.

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Volcanic rivers on Mars

12:53 pm

Granicus Valles

Cool image time! The photo on the right, cropped and reduced to post here, was part of the November image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO). If you click on the image you can see the full resolution picture.

The uncaptioned release webpage is dubbed “Faults in Granicus Valles.” The image itself only shows a small part of Granicus Valles, named after a river in Turkey, that flows down from the estern slopes of the giant volcano Elysium Mons. While far smaller than the four big Martian volcanoes in the Tharsis region to the east and near Marines Valles (which I highlight often), Elysium Mons still outshines anything on Earth at a height of almost 30,000 feet and a width of 150 miles. It sits at about the same northern latitude of Olympus Mons, but all by itself, rising up at the very northern edge of the transition zone between the southern highlands and the northern plains, with the vast Utopia Basin, the second deepest basin on Mars, to the west.

Overview of Elysium Mons and Granicus Valles

Granicus Valles itself is almost five hundred miles long. At its beginning it flows in a single straight fault, but once it enters the northern plains of Utopia Basin it begins to meander and break up into multiple tributaries. The MRO image above shows only a tiny portion in the northern plains, as illustrated by the white box in the overview map to the left.
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Evidence of nitrogen ice glaciers on Pluto

2:49 pm

Using data sent back by New Horizons during its fly-by of Pluto scientists now think they have identified land forms created by past nitrogen ice glaciers.

The washboard and fluted terrain … occur at the location on Sputnik Planitia’s perimeter where elevations and slopes leading into the surrounding uplands are lowest, and also where a major tectonic system coincides with the edge of Sputnik Planitia. The low elevation of the area makes it a natural setting for past coverage by nitrogen ice glaciers, as indicated by modeling of volatile behavior on Pluto performed by Dr. Bertrand at Ames.

Through comparison of the washboard and fluted texture with parallel chains of elongated sublimation pits (depressions in the surface formed where ice turns directly into a gas) seen in southern Sputnik Planitia, the ridges are interpreted to represent water ice debris liberated by tectonism of underlying crust. This water ice debris was buoyant in the denser, pitted glacial nitrogen ice that is interpreted to have formerly covered this area, and collected on the floors of the elongated pits. After the nitrogen ice receded via sublimation, the debris was left as the aligned ridges, mimicking the sublimation texture – washboard ridges where deposited on flat terrain, and fluted ridges where deposited on steeper slopes.

This is strange stuff. The solid bedrock here, water ice, will float on the nitrogen ice sitting on top of it. Thus, the material that wants to sublimate away, nitrogen, sometimes has to fight its way past the water ice that has risen to the top of the pile.

To put it mildly, we hardly understand these alien processes. This research is merely a first stab, the first hand-waving.

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More Pits on Mars!

3:30 pm

Pits near Arsia Mons

Cool image time! In the November image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO) were three images, dubbed by me in the collage above as number one, number two, and number three, showing pits south of Arsia Mons, the southernmost volcano in the chain of three giant volcanoes to the east of Mars’s largest volcano, Olympus Mons, and to the west of the Marineris Valles valley.

Mars overview showing pit locations

The image on the right provides the geographical context of the three pits. They are all south of the volcano on the vast lava flow plains that surround it. The location of pits #1 and #2 is especially intriguing, on the east and west edges of what appears to be a large lava flow that had burst out from the volcano, leaving a large lava field covering a vast area several hundred miles across just to the south. You can also see a similar large lava field to the north of the volcano. Both fields appear to have been formed when lava poured through the breaks created by the fault that cuts through the volcano from the northeast to the southwest.
» Read more

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The vast northern plains of Mars

3:33 pm

The vast northern plains of Mars

Cool image time! Actually, this image, found in the October image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO), is not that interesting, in its own right. Context is all!

The image on the right is a small section cropped and reduced in resolution from the full image, which you can see by clicking on it. It shows one of the only interesting features in this long image strip, a small mesa sticking out all by itself in a flat featureless plain pockmarked by various small craters.

The release has no caption, though it is entitled “Northern Plains Survey.” The northern plains, while having a lot of interesting features that attract the attention of planetary scientists and thus get photographed at high resolution, is mostly featureless, at least at the resolution of the wide field survey cameras on many Mars orbiters. In order to know what is really there, they need to take high resolution images systematically, of which this image is obviously a part.

Overview image

The problem is that there is so much ground to cover. This particular image was taken of a spot in the middle of the plains just to the north of the drainage outlets from Valles Marineris, as shown by the context map to the right. The tiny white spot to the right in the middle of the blue plains north of those drainage outlets is the location of this image.

Detail area of overview map

To understand how much ground needs to be covered, to the right is a close-up of the area shown by the white box in the first image above, with red rectangles indicating where MRO has already taken images. The white cross is the subject image. As you can see, most of this immense plain has not yet been imaged. It is almost as if they threw a dart to pick this one location. Most everything around it remains unseen at high resolution. Thus, to understand the geology of this one image is hampered because the surrounding terrain remains unknown, in close detail.

Mars is a big place. It is an entire planet, with the same land surface as the Earth’s continents. It still contains many mysteries and unexplored places. It will take generations to see it all.

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The steep slumping wall of a Martian volcano caldera

10:19 am

Caldera wall

Cool image time. The Mars Reconnaissance Orbiter science team today released a nice captioned image of the steep wall of the caldera of Ascraeus Mons, the northernmost of the three giant volcanoes that lie to the east of Olympus Mons, the biggest volcano of all. The image on the right, reduced and cropped, shows that steep wall, with full image available by clicking on it. The caption from the release focuses on the fluted upper parts of the wall.

We can see chutes carved into the soft dust that has built up on the slope, with some similarities to gully landforms elsewhere on the planet.

More revealing to me is how this image reveals the slumping that is slowing eroding the caldera’s walls while also making that caldera larger. First, the plateau above the cliff shows multiple small cliffs and pit chains, all more or less parallel to the wall. This suggests that the plateau is over time breaking apart and falling into that caldera. Think of it as an avalanche in slow motion, with the upper plateau separating into chunks as sections slowly tilt down toward eventual collapse. As these chunks separate, they cause cracks to form in that plateau, and hence the parallel cliffs and strings of pits.

On the floor of the caldera we can see evidence of past chunks that did fall, piled up in a series terraces at the base of the wall. These are covered with the soft dust that dominates Martian geology. That soft dust also apparently comprises much of the wall’s materials, and almost acts like a liquid as it periodically flows down the wall, producing the chutes at the top of the wall.

The weak Martian gravity here is an important factor that we on Earth have difficulty understanding. It allows for a much steeper terrain, that also allows structurally weaker materials to hold together that would be impossible on Earth.This image gives a taste of this alien geology, on a large scale.

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Stripes on Dione

2:55 pm

Using data produced by Cassini while orbiting Saturn scientists have discovered long narrow stripes on the moon Dione.

Dione’s linear virgae are generally long (10 to 100s of kilometers), narrow (less than 5 kilometers) and brighter than the surrounding terrains. The stripes are parallel, appear to overlie other features and are unaffected by topography, suggesting they are among the youngest surfaces on Dione.

“Their orientation, parallel to the equator, and linearity are unlike anything else we’ve seen in the Solar System,” Patthoff said. “If they are caused by an exogenic source, that could be another means to bring new material to Dione. That material could have implications for the biological potential of Dione’s subsurface ocean.”

That they cut across the topography implies strongly that they were laid down from above, after the surface irregularities were created.

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Giant ice pinnacles on Europa

9:15 am

In a new paper scientists note that getting the congressionally mandated Europa Clipper safely to the surface of Jupiter’s moon might be threatened by the existence there of forests of giant five-story high ice pinnacles.

Probes have shown that Europa’s ice-bound surface is riven with fractures and ridges, and new work published today in Nature Geosciences suggests any robotic lander could face a nasty surprise, in the form of vast fields of ice spikes, each standing as tall as a semitruck is long.

Such spikes are created on Earth in the frigid tropical peaks of the Andes Mountains, where they are called “pentinentes,” for their resemblance to devout white-clad monks. First described by Charles Darwin, pentinentes are sculpted by the sun in frozen regions that experience no melt; instead, the fixed patterns of light cause the ice to directly vaporize, amplifying minute surface variations that result in small hills and shadowed hollows. These dark hollows absorb more sunlight than the bright peaks around them, vaporizing down further in a feedback loop.

This work is based on computer models, so it has a lot of uncertainty. It also appears to assume that these pentinentes will be widespread across Europa’s equatorial regions, something so unlikely I find it embarrassing that they even imply it. I guarantee Europa’s surface will be more varied than that. If they are designing Europa Clipper properly, it will go into orbit first to scout out the best landing site, and will be able to avoid such hazards.

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Occator Crater on Ceres

9:14 am

Occator Crater

Cool image time! As Dawn’s long and successful mission to the asteroids Vesta and Ceres winds down, the spacecraft is taking a slew of spectacular close-up images of Ceres. The image on the right, cropped slightly to post here, is an oblique view of Occator Crater, home to the double bright spots that scientists now believe are caused by the upward seepage of a water-based brine from the interior.

The image was taken August 14, 2018 from a distance of 1149 miles. It clearly shows how the bright spots are depressions, not raised features. Additional images released this week of the floor of the crater capture a complex fracture network (seen here and here) with some fractures apparently quite deep.

All this suggests that the surface crust of Ceres is not very structurally strong, allowing a churning process that plows material up and down. The data also suggests that even on a small planetary body like Ceres the geological processes are going to be complex and often on-going, depending on material, energy, and the size of the body.

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Dust storms spotted on Titan

7:44 pm

Scientists reviewing Cassini data have identified dust storms for the first time of Saturn’s moon Titan.

When Rodriguez and his team first spotted three unusual equatorial brightenings in infrared images taken by Cassini around the moon’s 2009 northern equinox, they thought they might be the same kind of methane clouds; however, an investigation revealed they were something completely different. “From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of the year are not physically possible,” said Rodriguez. “The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude — much higher than the 6 miles (10 kilometers) that modeling tells us the new features are located.”

The researchers were also able to rule out that the features were actually on the surface of Titan in the form of frozen methane rain or icy lavas. Such surface spots would have a different chemical signature and would remain visible for much longer than the bright features in this study, which were visible for only 11 hours to five weeks.

In addition, modeling showed that the features must be atmospheric but still close to the surface — most likely forming a very thin layer of tiny solid organic particles. Since they were located right over the dune fields around Titan’s equator, the only remaining explanation was that the spots were actually clouds of dust raised from the dunes.

Obviously there are large uncertainties here. Nonetheless, the conclusion is a reasonable one, as it is expected that such dust storms would occur on Titan.

Posted just outside Zion National Park in the town of Springdale.

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Mountains on the Moon

1:53 pm

Mountains on the Moon

Cool image time! The image on the right, reduced slightly to post here, shows several high mountains on the far side of the Moon. If you click on the image you can see it at full resolution.

The summit of the unnamed peak in the foreground (50.2° S, 236.6° E) has an elevation of 6710 meters, about 7000 meters (about 23,000 feet) of relief relative to the low point at the bottom of the image. The two peaks on the horizon, 200 kilometers in the distance (about 125 miles), have summit elevations of 4320 meters (14,200 feet) and 4680 meters (15,350), respectively and both rise more than 6000 meters (almost 20,000 feet) above their surroundings.

In the Lunar Reconnaissance Orbiter (LRO) science team release in June, they noted that the high peak here is actually taller than Denali (Mount McKinley), the highest peak within the U.S. And it has no name. They also note that the peak is likely 4 billion years old, and has experienced extensive erosion in that time, meaning that it is also likely shorter than it once was.

I don’t have anything to add, other than this would be an amazing place to put up a resort, with trails taking you to the top of the mountains. In the lighter gravity, the hike would actually be somewhat easy, even wearing a spacesuit. And you wouldn’t have to worry about a thinning atmosphere as you climbed higher, as you do on Earth. You’d be carrying it with you.

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Baby volcanoes on Mars

9:41 am

Pitted cones on Mars

Most people are very aware of Mars’ giant volcanoes. This week the science team for Mars Reconnaissance Orbiter (MRO) decided to highlight instead a location on Mars filled with relatively tiny volcanoes. The image on the right is only one small section from the full image, and shows some of these pitted cones, as well the strange nearby badlands. From their caption:

The origins of these pitted mounds or cratered cones are uncertain. They could be the result of the interaction of lava and water, or perhaps formed from the eruption of hot mud originating from beneath the surface.

These features are very interesting to scientists who study Mars, especially to those involved in the ExoMars Trace Gas Orbiter mission. If these mounds are indeed mud–related, they may be one of the long sought after sources for transient methane on Mars.

The age of these pitted cones is not known. They might be still active, or have sat on Mars unchanged for eons.

Overview map

As always, context is crucial for gaining a better understanding of what we are looking at. The map on the right shows that these particular cones, indicated by the white cross, are located in an area of those plains dubbed Chryse Planitia, part of the vast northern plains of Mars, an area where some scientists think an intermittent ocean might have once existed. As you can see, this is also the region that took most of the apparent drainage running off the slopes of the planet’s giant volcanoes.

Nor are these cones unique in this region. MRO has taken a good scattering of images at this general location (41 degrees north, 332 degrees east), and throughout the surrounding terrain are many more of these pitted cones.

If these cones are a source of the transient methane on Mars, then the Trace Gas Orbiter should eventually see a concentration of methane above them. This would not prove them to be the source, but it would make them a much more intriguing target for a later rover mission.

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Looking for Marsquakes

1:24 pm

After eight and a half years of study of one particular very young fault system on Mars using high resolution images from Mars Reconnaissance Orbiter, scientists have found no evidence that any quakes occurred there in that time.

The team studied images of Mars’s surface over nearly a decade to look for changes that might have been caused by marsquakes. The researchers used images of Mars’s surface from the High Resolution Imaging Science Experiment (HiRISE) and applied Co-registration of Optically Sensed Images and Correlation (COSI-Corr)—software that has been validated to track terrestrial glaciers, landslides, and quakes on Earth, as well as dune movement on Mars itself—to hunt for signs of displacement near fault zones.

The researchers focused on the Cerberus Fossae fault system, the youngest fault system on the Red Planet and thus the most likely to still be active. They used the average coregistration performance of each study image to determine that this method should be able to detect fault slip rates of 0.1–10 millimeters a year.

The team identified only one displacement signal that could have been interpreted as evidence of a marsquake—but dismissed it as the result of a topographic artifact. Their results suggest that no seismic movement occurred in the Cerberus Fossae area over the course of the study, which spanned 8.5 Earth years’ worth of images from the planet.

This suggests, but does not prove, that Mars has very few quakes. We shall know more when InSight lands on Mars on November 26.

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Volcanic rills and lava tubes on Mars

9:34 am

Rills and lava tubes on Pavonis Mons

Cool image time! The image on the right, cropped somewhat to show here, was taken by Mars Odyssey of the southwestern slope of Pavonis Mons, the middle volcano of the line of three giant volcanoes located between the biggest volcano in the solar system, Olympus Mons, and the biggest canyon in the solar system, Marineris Valles. The slope goes down to the south, from the top to the bottom of the image. As noted on the image page,

The channel and nearby oval depressions are both related to the flow of lava. Narrow lava flows can create channels. The cooling of the top of the channel will form a roof over the flow, creating a tube beneath the surface. After the lava stops flowing the tube can empty, leaving a subsurface void. The roof will then collapse into the void forming the oval surface features.

I have added arrows to the image to draw your eye to the features that extend south in line with those oval depressions, eventually widening out to resemble a river delta, with the obvious rill probably indicating the lowest point in that delta.

Though the oval depressions are likely sections of a lava tube that collapsed, the features in line with those depressions suggest that the tube itself might still exist below the surface to the south, feeding into that delta where the rill meanders. It is also possible that my desire to find underground voids here, where glacier ice might possibly exist, might be skewing my conclusion. It could also be that the lava tube ended at these depressions, and what the features indicate is a wide surface flow, later embellished by the smaller flow of the meandering rill.

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A strange bulge on Mars

2:45 pm

Pollack Crater

Cool image time! The image on the right is not the cool image, but a context image of 59-mile-wide Pollack Crater, located slightly south of the Martian equator in the planet’s southern cratered highlands. What makes this crater intriguing to planetary scientists, and has prompted them to take many images over the decades, is the bulge in the southwest part of the crater’s floor. You don’t normally see a rise off-center like this inside craters. If there were any peaks, you’d expect them to be in the center, formed during the impact, when the crater floor melts and acts more like water in a pond when you drop a pebble into it, forming ripples with an uplifting drop in the dead center.

It therefore isn’t surprising that planetary scientists have taken a lot of pictures of this bulge, going back to the Mariner 9 orbiter in 1972, which first discovered it. Scientists then dubbed it “White Rock” because in the first black & white images it looked much brighter than the surrounding terrain. Later color images revealed that it is actually somewhat reddish in color, not white. As noted at this Mars Global Surveyor webpage,
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Ancient drainage on Mars?

9:49 am

Drainage on Mars?

Cool image time! The image on the right, cropped from the original to post here, was taken by Mars Odyssey on May 13, 2018, and shows what clearly looks like a point where a south-to-north drainage broke through a cliff wall to allow a liquid to flow down into the larger and deeper east-west flowing canyon.

The caption at the website for this image provides only a little analysis.

The right angle intersection of the depressions in this VIS image is one of the graben that form Sacra Fossae. The fossae are located on Sacra Mensa, near the beginning of Kasei Valles. Graben are depressions caused by parallel faults where a block of material drops down along the fault face.

According to this geological interpretation, the depressions initially formed due to this geological process. The image however suggests that a flow of liquid also played a part.

Overview map

This region, indicated by the white cross on the map to the right, is part of the vast drainages that flow down from Mars’ four giant Martian volcanoes. It is located north of Valles Marineris, the largest of all these drainages. This region is also where you find a lot of chaos terrain, which is what the hummocky depression at the bottom of the image resembles. Much of this mysterious geology is thought to have been formed by the liquid water that is theorized to have once flowed down from the volcanoes. Here, it appears that the liquid ponded in the depression at the bottom of the image until it found a path along the north-south graben to break through into the east-west deeper graben.

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Weird Martian crater?

1:17 pm

Weird crater on Mars

Time for another cool image! The image on the left, cropped to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on May 31, 2018, and shows a very strange layered mesa sitting in what looks like a crater or collapse feature. If you click on the image you can see the entire picture.

The location of this image is out in the middle of the vast northern plains of Mars. This region has few pronounced features, and generally sits at a lower elevation to the rest of Mars. It is suspected by some scientists that an intermittent ocean was once here, and that we are looking at the floor of a now dry sea.

This image was part of the July image release from MRO, and thus included no caption. They simply refer to it as a layered feature. It sits about a half mile (about 800 meters) to the west of a rough and indistinct cliff that drops down into an area of rougher terrain. This suggests that if this was formed by an impact, it cut down into that lower rougher layer, and since the impact there has been some upwelling from below creating the layered mesa.

I would not take my hypothesis very seriously, however. This feature could have nothing to do with an impact. It might also have been a mesa that now sits in a collapsed sinkhole. Or not. I could come up with many theories, all of which are likely wrong. What I do see here is something that geologically is very strange and baffling.

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Close-up of bright spot in Occator Crater

3:35 pm

Vinalia Faculae in Occator Crater

Cool image time! The Dawn science team today released some new images taken by the spacecraft in its final tight orbit around the dwarf planet Ceres. The image on the right is a cropped section of the full image. It shows some interesting details of part of one of the two bright spots in Occator Crater, dubbed Vinalia Facula, and was taken from a distance of 36 miles.

Other images show small bright spots in another small crater, fractures and interesting patterns in the floor of Occator crater, a dome in Occator Crater suggestive of underground processes pushing up, and other close-ups of its crater walls.

While all of these features are reminiscent of geology on Earth, none are really the same. Ceres’ light gravity and harsh environment, plus its history in the asteroid belt, requires alien processes that only hint at similarities to what we see on Earth.

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