Tag Archives: geology

OSIRIS-REx team confirms date for sample grab from Bennu

Nightingale landing site on Bennu
Click for full image.

The OSIRIS-REx science team has confirmed October 20, 2020 as the date the spacecraft will attempt a sample grab from the asteroid Bennu.

OSIRIS-REx is charged with collecting at least 2 oz. (60 grams) of Bennu’s rocky material to deliver back to Earth – the largest sample return from space since the Apollo program – and the mission developed two methods to verify that this sample collection occurred. On Oct. 22, OSIRIS-REx’s SamCam camera will capture images of the TAGSAM head to see whether it contains Bennu’s surface material. The spacecraft will also perform a spin maneuver on Oct. 24 to determine the mass of collected material. If these measures show successful collection, the decision will be made to place the sample in the Sample Return Capsule (SRC) for return to Earth. If sufficient sample has not been collected from [the primary landing site] Nightingale, the spacecraft has onboard nitrogen charges for two more attempts. A TAG attempt at the back-up Osprey site would be made no earlier than January 2021.

The press release at the link provides a lot of technical and interesting details about the sample-grab-and-go attempt, expected to put the spacecraft in contact with the asteroid’s surface for no more than sixteen seconds.

The maneuver itself is quite risky, as the available smooth landing area, as shown in the image above, is only half the size the equipment was designed for, and surrounded by large boulders.

Corroding glacier in crater rim gully?

Gully in crater rim
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Today’s cool image to the right, rotated and cropped to post here, shows a gully flowing down the north facing rim of a 30-mile-wide crater in the southern cratered highlands. It was taken on June 30, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

To my eye the corroded ridges and pits running down the western side of this gully look like a corroded ice, as if we are looking at a glacier that the light of the Sun, which in the southern hemisphere hits this north-facing slope more directly and for longer periods of time, is causing it to sublimate away with time.

The wider shot below shows the entire rim, flowing downhill from the south to the north.
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A patch of chaos in the Martian cratered southern highlands

A patch of chaos in the southern cratered highlands of Mars
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Today’s cool image, rotated, cropped, and reduced to post here, takes us to the cratered southern highlands of Mars. Taken by the context wide angle camera on Mars Reconnaissance Orbiter, this image shows us a strange isolated patch of what appears to be chaos terrain, which on Mars generally means an area of random knobs and mesas cut by canyons and channels.

The large bulk of chaos terrain on Mars is found near or in the transition zone between the lowland northern plains and the southern cratered highlands, and is thought to have been created by slow erosion, possibly by glaciers. This erosion process is aided by the gradient downhill from those highlands to the lowlands.

This location however is in the middle of the cratered highlands, and shows no obvious slope in any direction. And though the location is in the mid-southern latitudes, there is no obvious evidence of glaciers among these knobs and mesas. Furthermore, the mesas are not all the same height. Instead, a large portion appear to have been shaved off, as if some giant came in with a putty knife and scrapped away at them.

This can be clearly seen by the close-up below, taken by MRO’s high resolution camera on July 16, 2002 of the area indicated by the white box, which for scale is about 2 1/4 miles square.
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Martian channels within Martian channels

Channels within channels on Mars
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Whatever caused the meandering canyons on Mars, whether glaciers or liquid water, it was a process that was long-lived and multi-staged, as indicated by today’s cool image to the right, rotated, cropped, and reduced to post here. This photo, taken on June 28, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), shows a large canyon cutting downward from a high ridgeline to the north. As that canyon begins to flow out out of the mountains and into the plains to the south, a secondary inner channel appears, meandering down the center of the larger canyon.

This canyon is located at 35 degrees south latitude, in the mid-latitude region where scientists have found evidence of a lot of glaciers. In fact, there are some hints of eroded glacial material in the small channels to the west of this main canyon. Also, there appear to be patches of corroding glacial ice on the south-facing slopes of the east and west hills that define the main channel. In the canyon itself however there appear to be few if any glacial-type features.

The overview map below gives the location context.
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A hint of unexpected fresh ice on Enceladus

Two views of Enceladus
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Using data collected by Cassini while it orbited Saturn for thirteen years, scientists have found that there might be more relatively fresh ice on the surface of the moon Enceladus than previously believed.

Cassini scientists discovered in 2005 that Enceladus – which looks like a highly reflective, bright white snowball to the naked eye – shoots out enormous plumes of ice grains and vapor from an ocean that lies under the icy crust. The new spectral map shows that infrared signals clearly correlate with that geologic activity, which is easily seen at the south pole. That’s where the so-called “tiger stripe” gashes blast ice and vapor from the interior ocean.

But some of the same infrared features also appear in the northern hemisphere. That tells scientists not only that the northern area is covered with fresh ice but that the same kind of geologic activity – a resurfacing of the landscape – has occurred in both hemispheres. The resurfacing in the north may be due either to icy jets or to a more gradual movement of ice through fractures in the crust, from the subsurface ocean to the surface.

The image above, cropped, reduced, and rearranged to post here, shows two views of Enceladus. On the left we are looking at one hemisphere, with the south pole at the bottom. On the right we are looking straight down at the south pole. The red areas are where scientists think there is relatively fresh ice. While the new ice is very pronounced at the south pole, where the tiger-striped vents have been found, the northern ice is much less evident, though clearly there.

That northern fresh ice however might not come from the planet’s interior, as suggested by the press release. It might also be new ice deposited from space that came from those very active tiger stripes. At the present time the data doesn’t allow for any solid conclusions.

Martian crater filled with lava

Lava filled Martian crater
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Cool image time! Unlike most of the recent images I’ve posted from Mars, today’s has nothing glacial about it. Instead, the photo to the right, cropped to post here, shows us a crater where lava broke through the southern rim to fill its interior.

The picture was taken on July 15, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The crater is located within what I call volcano country on Mars, just inside the Athabasca Valles lava field, what some scientists believe [pdf] is the youngest lava field on Mars, estimated have occurred less than 600 million years ago.

The overview map below provides context.

Overview map

The tiny white box south of Elysium Mons indicates the location of this crater. The dark blue areas indicate the extent of the Athabasca lava field. The Medusae Fossae Formation is the largest volcanic ash deposit on Mars.

The Athabasca lava field is about the size of Great Britain, and is thought to have been laid down in only a matter of a few weeks. When it spread it clearly reached this crater, the lava pushing through to fill it. If you look at the full image you can see that the north-trending lava flow even continued past the crater a considerable distance on both sides, the crater acting like a big rock in a stream, blocking the flow.

Since this happened more than half a billion years ago, a lot of erosion has occurred, mostly between the crater’s rim and the edge of the ponded but now solidified lava.

Unexplored Mars

Strange crater on the edge of Argyre Basin
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The constant stream of images and data that our orbiters and landers are feeding down to us from Mars can sometimes give the impression that the red planet is being thoroughly explored. Today’s cool image illustrates how this impression is false, and instead shows a hint of what remains untouched on the fourth planet from the Sun, a planet with the same land area as on Earth.

The photo to the right, cropped and reduced to post here, was taken by the high resolution camera of Mars Reconnaissance Orbiter (MRO) on May 10, 2020, and shows a strange crater on the north interior edge of Argyre Basin, one of Mars’ largest basins located in the southern hemisphere. Not as deep or as large as Hellas Basin, what I call the basement of Mars, Argyre is still the second largest such basin on Mars, about 1,100 miles in diameter with its lowest elevation 17,000 feet below the surrounding southern cratered highlands. Like Hellas, it is thought to be the remains of major impact.

The point of this post is not to try to explain the geology of this crater. Located at 45 degrees south latitude, it might or might not be showing us glacial evidence. The nature of the terrain is inconclusive. To figure out the geology here would require a lot more data, and a focused interest in studying it.

Instead, this image shows us how little we know of Mars. For example, this photo was not requested by any scientist doing specific research. It was requested instead by the science team for MRO’s high resolution camera because they need to take images at regular intervals to maintain the camera’s temperature, and if no one has requested an image for a specific time period, they make their own choice, picking a spot that might be interesting without knowing sometimes what they might find. Often such “terrain sample” images are somewhat boring. Other times they reveal some surprisingly interesting geology.

The map below gives a sense of how little of the Argyre Basin has been explored by MRO’s high resolution camera.
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The frozen and changing mid-latitudes of Mars

Glacial erosion on Mars
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Using “frozen” and “changing” to describe any single location might seem contradictory, but when it comes to the mid-latitudes of Mars, high resolution images keep telling us that both often apply, at the same time and at the same place.

The photo to the right, rotated, cropped, and reduced to post here, is a typical example. Taken on May 8, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), it shows what the scientists label as “mesas and ridges.” Drainage is to the south, and it sure looks like some sort of glacial flow is working its way downward within the canyons between those mesas.

Overall the terrain has the appearance of a frozen ice sheet, or at least terrain that has a shallow ice table close to the surface. It also looks like chaos terrain in its infancy, the erosion process not yet cutting down enough to make the mesas stand out fully.

The location of these mesas and ridges is shown in the context map below, which also shows that this location is at the same latitude as SpaceX’s Starship prime Martian landing site, and only about 400 to 500 miles to the east.
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The alien Red Planet and the scientific method

Spiders, dunes, and strange terrain in high latitude southern Martian crater
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As a child growing up in the 1950s and 1960s and an avid reader of science fiction, I was constantly presented with stories about Mars and what people imagined it was like. At the time no spacecraft had as yet gotten a close look at the planet, so the theories of a desert planet, with many canals built by an alien race attempting to stave off death as the planet’s water disappeared, were still considered possible. So were theories that the changing colors across its surface seen seasonally in ground-based telescopes suggested the possibility of some form of lichen-like life that came and went with the seasons.

None of those fantasies have turned out to be true. All attempted to create an alien planet in the model of Earth, and thus were guaranteed to get it wrong. After a half century of increasingly sophisticated research, we now know a bit more about what Mars is like, and have learned that it is much stranger than we had imagined, an icy world quite possibly shaped by slowly shifting glaciers and ice sheets, creating surface features in ways so alien from what we are familiar with on Earth that even now scientists struggle to figure those processes out.

The photo above and to the right, taken on May 25, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), is a perfect example. At first glance it fits what I call a “what the heck?” image. Without knowing more, it is impossible to figure out what we see here.

The wider image below, taken by context camera on MRO, provides our first clue.
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Sharp Martian ridges sticking up from the dust

Sharp ridges sticking up from Martian dust
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Today’s cool image brings us back to the region of Mars where the rover Opportunity journeyed. Taken on June 25, 2020 by the high resolution camera on Mars Reconnaissance orbiter (MRO), the photo to the right, cropped and reduced to post here, focuses on some sharp but low ridges that appear to stick up out of the Martian dust, hinting that they are the tops of some larger feature buried over the eons and only now revealed partly by recent erosion. I estimate that their height is roughly one to two hundred feet or so.

This image is in Arabia Terra, the widest and largest transitional zone region between the northern lowland plains and the southern cratered highlands. It is also only about 200 miles north of where Opportunity landed, and about 230 miles from where it died after almost fifteen years of operation, on the west rim of Endeavour Crater. The overview map below gives the context.
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A Martian starburst spider

A Martian starburst spider
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Cool image time! The photo to the right, cropped to post here, illustrates an example of a wholly unique Martian phenomenon, that is not only unique to Mars but is also found only in its south polar regions. The image was taken on July 17, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

What we are looking at is a permanent spider formation etched into the layered deposits of ice and dirt that cover the widest area surrounding Mars’ south pole. The blue dot just north of Chasma Australe on the overview map below shows the location of these starbursts, on those layered deposits.

Each winter the poles of Mars are blanketed with a thin mantle of dry ice, generally less than six feet thick. When spring arrives and sunlight hits this mantle, it heats the ice and sand on which the mantle lies, and that warmth causes the mantle’s base to sublimate back into gas. Eventually gas pressure causes the mantle to crack at its weak points so the gas can escape. By the time summer arrives that mantle is entirely gone, all of it returning to the atmosphere as CO2 gas.

This sublimation process differs between the north and south pole, due to the different terrain found at each. In the north the mantle mostly lies on ice or sand dunes, neither of which is stable over repeated years. Thus, the mantle weak points do not occur at the exact same place each year, even though they occur at the same type of locations, such as the base and crests of dunes.
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Bennu tosses particles from its surface routinely

Objects ejected from Bennu
Tracked particles after August 28, 2019 ejection event.

During OSIRIS-REx’s more than twenty months flying close to the Bennu, scientists have found that the asteroid routinely kicks particles from its surface into space, with these events linked to the asteroid’s day-night cycle.

Since arrival the scientists have seen and tracked more than 300 ejection events, with the almost seven hundred objects detected ranging from about an eighth to a half inch in size. Most moved about eight inches per second, comparable to “a beetle scurrying across the ground.”

The image to the right, cropped, reduced, and brightened to post here, comes from the introductory paper of a suite of papers on the subject, published today.

The timing of the events however reveals the most.

As Bennu completes one rotation every 4.3 hours, boulders on its surface are exposed to a constant thermo-cycling as they heat during the day and cool during the night. Over time, the rocks crack and break down, and eventually particles may be thrown from the surface. The fact that particle ejections were observed with greater frequency during late afternoon, when the rocks heat up, suggests thermal cracking is a major driver. The timing of the events is also consistent with the timing of meteoroid impacts, indicating that these small impacts could be throwing material from the surface. Either, or both, of these processes could be driving the particle ejections, and because of the asteroid’s microgravity environment, it doesn’t take much energy to launch an object from Bennu’s surface.

The link includes a cool movie showing the ejections events and the tracked paths of the ejected particles.

Another pit on Mars!

Isolated small pit on Mars
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It has been several months since my last Martian pit update, mostly caused by the lack of new pit images coming down from the high resolution camera on Mars Reconnaissance Orbiter (MRO). I think this lack is not because of a lack of additional pits or caves but instead signals the completion of a first high resolution survey of the known pits so far found on Mars. A full list of all past pit updates can be found at the bottom of this post.

Regardless, the image to the right, cropped to post here, is the only such image in months, taken on April 14, 2020, and shows a small isolated pit in the lava slopes between the giant volcanoes Arsia and Pavonis Mons. In the full photograph you can see how isolated is this pit. To the limits of the image there are no other such features, the terrain a relatively smooth plain with only some small ridges and and a scattering of what seem to be partly obscured or eroded small craters.

The overview below map shows this pit’s relationship to the volcanoes as well as to all other known nearby pits.
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Strange glacial flow features on Mars?

Flow features in Reull Vallis
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on May 26, 2020, and shows what the scientists dub “Flow features in Reull Vallis.”

These features are typical in the mid-latitudes, and once again suggest the presence of buried glacial ice. The two lobes on the left and right both evoke such flows, as does the material in the drainage channel near the top of the photo.

What is more intriguing however are the strange features in the box. Below is that section, at full resolution.
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The icy Erebus Mountains near where Starship will land on Mars

Overview of all SpaceX images in Arcadia Planitia

Glacial filled crater in Erebus Montes
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It has been several months since I posted any new photos of the region on Mars which SpaceX considers its prime candidate landing site for its Starship spacecraft/rocket, now under development. The map to the right shows the location of all the images that SpaceX has obtained from the high resolution camera on Mars Reconnaissance Orbiter (MRO) of this landing region, located in the northern lowland plains at the border between Arcadia and Amazonis and to the east of the Erebus Mountains. (See my post on November 13, 2019 for an analysis of the reasoning for SpaceX to choose this region, along with links to each of the numbered images.)

Time to take another look, this time at the very center of the southern cluster of the Erebus mountains. The crater to the right, its location indicated by the tiny red rectangle on the map above, was taken by MRO on May 6, 2020, and shows the typical glacial features scientists find in mid-latitude Martian craters. The floor appears filled with glacial material, with the repeated cyclical flows repeatedly coming down off the north-facing interior rim. That rim would generally be colder and get less sunlight, so snowfall is more likely to pile up there and then flow downward like a glacier, only to sublimate away once it moves out of shadow.

What makes these mountains enticing, only about 400 miles from the Starship landing zone, is not simply what is inside this crater, but what surrounds it. Below is the wider view provided by MRO’s context camera.
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InSight has buried its Mole

The Mole buried

Using the scoop on InSight’s robot arm, engineers have now successfully filled the large hole that had formed around the spacecraft’s mole, the drill that has been trying but failing to dig down about fifteen feet so that a heat sensor could measure the internal temperature of Mars.

The image to the right shows the filled hole with the mole’s communications tether snaking away. Earlier this month they used InSight’s scoop to scrape surface material into the hole, as planned in June. According to the mole’s principle investigate, Tilman Spohn,

I had estimated that the first scrape of 12 centimetres swath length would raise the bottom of the pit but leave the Mole sticking out of the sand. By the way, this was the condition for some to agree to the quite controversial ‘scratch test’. As one can see in the image from Sol 600 shown below, that estimate was not quite right. The scraping was a complete success! The scrape was much more effective than expected and the sand filled the pit almost completely. The Mole is now covered, but there is only a thin layer of sand on the back cap.

Their next step will be to use the scoop to press down on the dirt of the filled hole, with the hope this added pressure will keep the dirt pressed against the mole as it hammers downward, thus holding it place with each downward stroke.

Bright-tipped perplexing terrain on Mars

Perplexing terrain on Mars
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The photo to the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on June 24, 2020, and shows a bit of inexplicable country in Arabia Terra, the widest and largest transition zone region on Mars between the northern lowland plains and southern cratered highlands.

The stuff visible in this image falls into what I call “What the heck?” geology. It is very clear we are looking at a collection of straight and curved ridges and mesas, all of which for some reason are bright at their tips and edges. Some of the curved ridges might be the rims of craters, but only some. Other ridge lines look more like leftovers following a strange erosion process. The problem is that to my uneducated eye I can find little rhyme or reason to these shapes. The mesas and canyon on the image’s right edge might be explained by the erosion processes that create chaos terrain on Mars, but that process does not do a good job of explaining anything else in the photo.

That this uncaptioned image is merely labeled “Arabia Terra” suggests that the scientists involved in getting this image were equally perplexed by it, and could not give it a better description.

The overview map below provides some location context, including how this geology relates to the landing site of Europe’s Rosalind Franklin rover, now scheduled for a 2022 launch.
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The longest lava tube in the solar system?

A lava tube on Mars
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Before I delve into today’s cool image, I think it important to explain to my readers why I seem to post so many cool images from Mars. The simple explanation is that Mars right now is where almost all the cutting edge planetary research is taking place, and as a science journalist focused on space exploration I must go to that cutting edge. My dear readers know that I love variety (just consider the evening pauses on Behind the Black), but you can’t ignore the reporting of real discoveries simply to increase the diversity of one’s posts. This is too often what modern news outlets do, which is also why they often miss the real story.

Anyway, today’s cool image to the right, rotated, cropped, and reduced to post here, shows only a small section of what might be the longest lava tube in the entire solar system. Taken on May 5, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), it shows a string of pits along a meandering depression coming down the northwest flank of the giant volcano Arsia Mons. The image was a follow-up to a July 2014 photo of the same location, and was taken to produce a stereo pair.

The feature strongly suggests a lava tube, with the pits being skylights into the meandering underground void. From top to bottom this section of the tube is a little over three miles long. Since there are lava tubes on Earth far longer, this one image hardly makes this the longest tube in the solar system.

The tube, however, extends off the image both at the bottom and at the top. Not many high resolution images have been taken in this area, so it is therefore hard to say how far the tube extends. Other nearby high resolution images in this area however have found similar lava tubes, which conceivably could be part of the same tube. The overview map below shows the relationship.
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A collapsed Martian crater in a glacier?

Collapsed crater in glacier?
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Today’s cool image to the right, cropped and reduced to post here, is another example of evidence that the mid-latitudes of Mars are covered with glaciers and ice. The photo, taken on April 25, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), shows many of the squashed and blobby features found in these mid-latitudes.

What makes the image even more interesting is the small crater in the center of the larger crater. The floor of that larger crater seems filled with glacial fill, and it appears that when that smaller impact occurred it caused the nearby surrounding fill to collapse downward, producing the oblong off-center depression. At least that’s my uneducated guess, which I admit could easily be wrong.

Even if my hypothesis is wrong, the visual evidence here supports the theory that this region, dubbed Deuteronilus Mensae, has lots of buried ice glaciers. Consider for example the distorted crater to the southwest of the big crater. It sure looks like at some point it was heated suddenly, maybe by the impact of the main crater, so that its rim was warped and reshaped, in the manner that ice would be warped and reshaped by sudden heat. Moreover, all the craters in full image appear to have glacial fill.

The overview map below adds weight to this conclusion.
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Revisiting Mars’ glacier country

Glacial cracks or pits on Mars
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With today’s cool image we return to what I have labeled glacier country on Mars, though this time the image shows a Martian glacial feature that while resembling vaguely such features seen on Earth, has an alienness to it that requires some explanation.

The photo to the right, cropped to post here, was taken on March 24, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The section I have focused on is the floor of a depression with a number of parallel pits, more or less aligned with the packed north-south ridges that cover the entire floor.

Normally, the north-south ridges would suggest repeated glacial flows moving to either the west or to the east. Such movement could over time, cause the ridges to separate, creating the cracks or pits that we see here. The trouble is that the slope of this depression is very unclear. In fact, the wider view below shows that this depression appears mostly enclosed, or if not it does not seem to be flowing in any particular direction.
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Cracks and scallops on the lowland plains of Mars

Utopia Basin cracks and scallops
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Cool image time! To the right is some of the strange terrain seen in the northern lowland plains of Mars. The photo, cropped to post here, was taken on May 4, 2020 by the high resolution camera of Mars Reconnaissance Orbiter (MRO) of an area in the northwest part of Utopia Planitia.

Next year China’s first attempt to soft land a rover on Mars will occur somewhere in Utopia Planitia. Utopia Planitia, also called Utopia Basin, is quite large, however, and in fact is the largest recognizable impact basin on Mars, with a diameter of more than 2,000 miles or about two thirds the width of the United States. If this strange spot was put near Seattle, Tianwen-1 is expected to touch down somewhere near Houston, Texas.

The MRO science team labeled the image “Scalloped terrain in Utopia Planitia.” The curved cliffs in the image illustrate those scallops, found frequently in Utopia. Their formation is believed related to the sublimation of underground ice, changing directly from ice to gas. The theories of this process however are somewhat uncertain at this time.

What stuck me about the image were the north-south oriented cracks. They extend through the full image, all oriented in the same direction. I haven’t the faintest idea what caused them, but they are intriguing, are they not?

This terrain is also different than most Utopia Planitia images I have previously posted. Most look squishy and blobby and distorted, suggesting the presence of soft slush and underground ice. This image instead suggests hard bedrock, even though it is farther north than the previous images and should thus be expected to have more ice underground. Quite mysterious.

I suspect the ice is here, but is simply not made obvious by any surface event. Then again, who knows? The geology of Mars is definitely not obvious, no matter how obvious it sometimes seems.

More glaciers and eroding gullies on Mars

Crater with gullies and glacial fill
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Cool image time! The photo to the right, cropped and reduced to post here, shows the interior south-facing rim of a small crater in the southern cratered highlands of Mars. Taken on May 30, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), the image release is merely labeled “Gullied Slope”. The photo was taken as part of regular monitoring of these gullies since 2011 to see if they change from season to season. The 2011 image was captioned by planetary scientist Alfred McEwen, who wrote the following about the gullies:

These are erosional features with depositional fans. Some of the gully fans have a bluish color: these are probably quite recent deposits, less than a few tens of years old.

Since they were considered so very young, it makes great sense to look at them frequently. In making a quick comparison between the 2011 and 2020 images however I could not spot any changes, but that might be because the versions I downloaded are not at the fullest resolution.

This crater, at 39 degrees south latitude, is also worthwhile because its floor appears covered with glacial material, what scientists have dubbed concentric crater fill. As McEwen noted in his 2011 caption,

On the floor of the crater (bottom of this image) are ridges that likely formed from the flow of ice, perhaps a few million years ago.

Those glaciers, generally protected by thin layers of dust and debris, are considered inactive at this time in Martian geological history. The many ridges however hint at the many many cycles in the Martian climate, fluctuating between periods when these mid-latitude glaciers were growing while the polar ice caps were shrinking, and periods when the mid-latitude glaciers were shrinking while the polar ice caps were growing.

Wormlike glacier on Mars

Glacial flow in the mid-latitude southern cratered highlands
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Cool image time! The image to the right, cropped and reduced to post here, shows a very typical glacial-type feature found frequently in the mid-latitudes of Mars. Taken on May 23, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), it is labeled a “Lobate Flow Feature within Channel in Nereidum Montes.” Nereidum Montes is a rough mountainous region along the northwestern margin of Argyre Basin, the second largest impact basin on Mars, after Hellas Basin.

Scientists using Europe’s Mars Express orbiter have already found a great deal of glacial evidence in these mountains. I have also posted images of other glacial features on the north edge of Argyre. This image just reinforces that data.

This particular glacier however resembles the kind of glaciers one sees on Earth more than most Martian glaciers. As it meanders down its valley, large cracks form near its edges as friction slows their passage and drags them apart. In fact, the glacier itself might have very well carved the canyon. According to Dan Berman, senior scientist at the Planetary Science Institute in Arizona, who had requested this image,

While I can’t say for sure, the canyon was likely formed by a glacier. Whether or not the ice that remains today is part of that glacier, or one that formed later, is impossible to say.

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The colors of Mars

The different colors of Mars
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Actually today’s cool image tells us less about the real colors on Mars and much about the colors captured by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The photo on the right was taken on May 2, 2020, and shows a relatively featureless area to the east of 80-mile wide Byrd Crater in the high southern latitude of Mars.

The only major features seen on this photo are a series of rounded ridges that in the larger context map at the image site look almost like drainage hollows coming down from the crater’s rim about twenty miles away.

The colors, though exaggerated and not entirely as the eye would see them, still tell us something very real about the surface. As explained here [pdf]:

In spite of the variable level of color enhancement for the Extras products, we can make some generalizations to better understand what the stretched color images are showing. Dust (or indurated dust) is generally the reddest material present and looks reddish in the RGB color. … Coarser-grained materials (sand and rocks) are generally bluer … but also relatively dark, except where coated by dust. Frost and ice are also relatively blue, but bright, and often concentrated at the poles or on pole-facing slopes. Some bedrock is also relatively bright and blue, but not as much as frost or ice, and it has distinctive morphologies.

Thus, this photo is telling us that the lower areas are covered with dust (the red), while the rounded ridgelines are covered with coarser and bigger rocks. The brightest blue, which is facing towards the south pole, might also indicate frost or ice.
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Hubble photographs Comet NEOWISE

Comet NEOWISE, photographed by the Hubble Space Telescope
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Using the Hubble Space Telescope, astronomers have obtained close-up images of Comet NEOWISE after it had survived its closest approach to the Sun. The photo to the right, cropped and reduced to post here, is one of Hubble’s two images.

Comets often break apart due to thermal and gravitational stresses at such close encounters, but Hubble’s view suggests that NEOWISE’s solid nucleus stayed intact. This heart of the comet is too small to be seen directly by Hubble. The ball of ice may be no more than 4.8 kilometres across. But the Hubble image does captures a portion of the vast cloud of gas and dust enveloping the nucleus, which measures about 18 000 kilometres across in this image.

Hubble’s observation also resolves a pair of jets from the nucleus shooting out in opposite directions. They emerge from the comet’s core as cones of dust and gas, and then are curved into broader fan-like structures by the rotation of the nucleus. Jets are the result of ice sublimating beneath the surface with the resulting dust/gas being squeezed out at high velocity.

Below the fold is a six-second movie made of Hubble’s two images, showing how the jets changed over a three hour time period on August 8th.
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Mars: On the floor of Valles Marineris

Strange flow (?) on floor of Valles Marineris
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Cool image time! The image to the right, rotated and cropped to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on May 14, 2020, and shows a very strange bright outcrop on the floor of Valles Marineris, the largest canyon on both Mars and in the entire solar system.

MRO has photographed this spot a few times since 2007. The first image was posted with a detailed caption by Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona, who described the feature like so:

Most of the material is light and shows many small scarps or benches. In places these appear to indicate boundaries between layers, but they are often discontinuous. The light material is buried by a thin mantle of dark material in places; the dark material is from other rock layers—possibly those above the outcrop—and has fallen or been blown over the light rock.

Near the top of the outcrop, there is a distinctive layer that appears as a dark band at low resolution. At the full resolution of HiRISE, this appears to be a layer breaking up into angular boulders, indicating different rock properties than the underlying light rock. There does appear to be some light material above this layer, suggesting that the process that deposited the light material continued for some time.

Dundas also added that the lighter material is theorized to have “formed by a variety of processes. Proposed deposition mechanisms for light-toned sediments on Mars include those from rivers or lakes, volcanic ash or wind-blown sand or dust.”

Since this lighter colored outcrop has remained as bright as it has now for more than six Martian years, I doubt it is brighter because of the surface deposit of ash, sand, or dust (though it might be made of these materials which have now become hardened). My guess is that the brightness is inherent to the outcrop. Moreover, note the plateau to the southwest. Its rim is cut sharply, suggesting erosion revealed this outcrop, and that the outcrop is made of more resistant material.

The overview map provides some context that also might help explain the geology at this location.
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Movie of OSIRIS-REx’s last rehearsal before sample grab

Closest point to Nighingale landing site during OSIRIS-REx's last rehearsal
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The OSIRIS-REx science team has released a movie made by the spacecraft’s navigation camera during its August 11th final rehearsal prior to the planned sample grab-and-go now set for October.

The image to the right is a capture of one image when the spacecraft was closest to the asteroid, about 131 feet above the surface. The target landing site, dubbed Nightingale, is the somewhat smooth area near the top half of the frame.

These images were captured over a three-hour period – the imaging sequence begins approximately one hour after the orbit departure maneuver and ends approximately two minutes after the back-away burn. In the middle of the sequence, the spacecraft slews, or rotates, so that NavCam 2 looks away from Bennu, toward space. Shortly after, it performs a final slew to point the camera (and the sampling arm) toward the surface again. Near the end of the sequence, site Nightingale comes into view at the top of the frame. The large, tall boulder situated on the crater’s rim (upper left) is 43 feet (13 meters) on its longest axis. The sequence was created using nearly 300 images taken by the spacecraft’s NavCam 2 camera.

Nightingale might be their best choice, but it remains about half the size they had originally wanted for their grab-and-go site, with far too many objects larger than planned. They designed the grab-and-go equipment to catch objects smaller than 0.8 inches. Little at this location, or on the entire surface of Bennu, is that small. The asteroid is truly a pile of gravel, with no dust.

Majestic dunes on Mars

Beautiful dunes on Mars
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter on May 10, 2020, and shows the dune field inside a large unnamed sixty-mile-wide crater in the highlands of Mars.

Scientists have been using MRO to monitor this site to track both dust devils and dune changes since at least 2009. In 2009 the focus was on the numerous dust devil tracks, and in fact I posted in March 2020 a comparison of an earlier image with a more recent picture, showing how the earlier tracks had vanished in recent pictures, probably wiped clean by the global dust storm in 2018.

This time however I am less interested in the science, which I covered in detail in that previous post, but in the beauty of these dunes. They are large and majestic, and the color strip tells us that they exhibit striking colors of green, gold, and tan. Is there a place on Earth with dunes of such colors? If so, it is rare.

Make sure you click on the image to see the full resolution photograph. It is even more breath-taking.

Mars: A small volcano at the base of a big volcano

Volcanic vent near Pavonis Mons
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Today’s cool image is of a recent high resolution image taken on May 30, 2020 by Mars Reconnaissance Orbiter (MRO) of what they label as a volcanic vent near Pavonis Mons, the middle giant volcano in the string of three that sit between Olympus Mons, the biggest Martian volcano in the solar system, and Valles Marineris, the biggest canyon in the solar system.

MRO took a previous picture of this vent back in 2010, when they labeled it instead a “small volcano.” Both labels are essentially correct. The two depressions here clearly were a vent for lava at some point in the past. The depressions also fit the definition of a small volcano, as they sit at a high point with two rills flowing down from them. In some ways they could be considered small calderas at the top of a volcano.
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Bottom edge of Martian glacier?

The foot of an inactive glacier on Mars
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Today’s cool image, taken on May 25, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), provides a nice example of the typical foot of an inactive buried glacial flow on Mars. The image to the right, rotated, cropped, and reduced to post here, focuses on the center of the full image. Uphill is to the right. The glacier’s edge runs down the middle left of the photo.

Scientists call this a lobate flow because its shape resembles a lobe, smooth and rounded as it comes down the slope. Located at 38 degrees south latitude to the east of Hellas Basin and just to the north of one of that basin’s major infeeding canyons, Harmakhis Valles, this flow comes down the west side of a large mountain. The overview map below provides the context, with the white rectangle indicating the photo’s location.
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