An icy hollow on Mars

A icy hollow on Mars
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Cool image time! The photo to the right, cropped, reduced, and enhanced to post here, was taken on August 20, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a somewhat typical example of the many ice scarps that scientists have identified in MRO pictures.

Though this is not a hard fast rule, most of the ice scarps so far found tend to have the steep cliff on the pole-facing side, with the scarp very slowly retreating towards the equator. In today’s example, the scarp where an ice layer in the cliff wall has been identified is indicated by the white arrow, though three sides of the hollow, on the east, north, and west sides, could all also have exposed ice.

Nor is that the only likely ice at this location at 56 degrees south latitude. The stippled plain surrounding the hollow clearly looks like an eroded ice layer, likely covered with a thin protective coat of dust to protect if from quickly sublimating away. The dark streaks across this surface are likely dust devil tracks.

As documented by the global map below, Mars is like Antarctica, a desert with water ice everywhere.
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Visible clean water ice on Mars

Crater with ice scarp
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Cool image time! The photo to the right, cropped and reduced to post here, is today’s picture of the day for the high resolution camera on Mars Reconnaissance Orbiter (MRO). Taken on September 13, 2021, it shows an exposed scarp on the southern inner wall of a small 800-foot-wide crater.

What makes that scarp intriguing is its blue color. As noted by Shane Byrne of the Lunar and Planetary Lab University of Arizona, who wrote the caption:

This north-facing cliff appears to expose icy material that’s similar to other pole-facing scarps showing buried ice elsewhere on the planet. These cliffs give us a cut-away view of the buried ice in that location and can help answer questions about what the Martian climate was like when this ice formed.

The crater itself sits inside a much larger crater, as shown in the wider picture below.
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Holes in snowy ice on Mars?

Holes in snowy ice on Mars?
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Cool image time! Today we return to the regions surrounding Milankovic Crater in the high northern latitudes of Mars. The photo to the right, cropped and reduced to post here, was taken on June 1, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a spray of impact craters where the bolides apparently landed in relatively soft material. The location itself is about 10 miles to the southeast of the 74-mile-wide crater, and sits within its rim ejecta blanket.

The label for the image says this is showing “crater modification,” which suggests that the rimless nature of these craters became so after their creation. This location, at 54 north latitude, is in a region of Mars where scientists have found a lot of evidence of near surface ice. For example, within Mikankovic Crater itself they have identified numerous scarps with clearly seen pure ice layers.

If ice is close to the surface here, then the ground could be like soft snow on Earth, especially because Mars’ lighter gravity would not compress that ice as much. Think about what happens when you toss pebbles into soft snow. They fall through, and leave behind holes not unlike the ones we see in this picture. Later, sunlight would begin to modify the holes so that their edges grow outward, once again exactly as we see here.

The overview map below as always gives some context, which in this case has less to do with Mars but with Elon Musk and Starship.
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Scallops of Martian ice

Scallops of Martian ice
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Cool image time! The photo to the right, cropped to post here, was yesterday’s captioned image from the MRO science team. From the caption, written by Shane Byrne of the Lunar and Planetary Lab University of Arizona,

About a third of Mars has water ice just below the dusty surface. Figuring out exactly where is vital for future human explorers. One of the ways scientists do this is to look for landforms that only occur when this buried ice is present. These scallops are one of those diagnostic landforms.

A layer of clean ice lies just below the surface in this image. As the ice ablates away in some spots the surface dust collapses into the hole that’s left. These holes grow into the scallops visible here as more and more ice is lost.

You can see those holes near the top of the scallop’s slopes.
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Cliffs of Martian ice

southern hemisphere Martian ice scarp
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Today’s cool image to the right, cropped to post here, shows an ice scarp located in the high southern latitudes south of Hellas Basin. It was taken on August 15, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and was released today as a captioned image. From the caption:

Scientists have come to realize that, just below the surface, about one third of Mars is covered in ice. We study this ice to learn about Mars’ ancient climate and astronauts’ future water supplies.

Sometimes we see the buried ice because cliffs form like the one in this image. On the brownish, dusty cliff wall, the faint light-blue-colored ice shows through. [emphasis mine]

This ice scarp is one of about two dozen [pdf] that have so far been found within the latitude bands of approximately 45 to 65 degrees latitude in both the north and south hemispheres. The data so far obtained suggests that the scarp exists because of a pure water ice layer just below the surface. Over time this pole-facing cliff retreats away from the pole towards the equator, leaving behind it an extended pit. In the cliff wall scientists think they have detected evidence of that water ice layer.

Blue in MRO hi-res images can indicate both water as well as very rough surfaces. While much of the blue here could be ether, the blocky cracks suggest it is ice. As explained by Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona and lead author of the pdf above,

The crack patterns are likely thermal contraction cracks, which form in shallowly buried ice due to seasonal temperature changes causing it to expand and contract. When that repeats over many years it creates regular patterns of cracks that organize themselves into polygons.

The overview image below gives the location of all known such scarps, as of March of 2020, taken from the pdf paper that I linked to above.
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Big scallops in the Martian southern latitudes

Big scallops on Mars
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, shows an example of some large scalloped depressions in the high southern latitudes of Mars.

Taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on June 27, 2020, these scallops resemble in many ways the ice scarps that scientists have previously found at this same latitude, both to the east and west of where these scallops are located. With those scarps, the data suggests that a very pure layer of ice is visible in the cliff face, and that over time the cliff retreats northward due to sublimation of that ice.

The scallops in the photo to the right suggest the same process, though the differences raise questions. As explained by Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona,
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The range for exposed ice scarps on Mars keeps growing

Overview of ice scarp locations on Mars

In January 2018 scientists announced the discovery of eight cliffs with visible exposed ice layers in the high mid-latitudes of Mars. At the time, those eight ice scarps were limited to a single crater in the northern hemisphere (Milankovic Crater) and a strip of land in the southern highlands at around latitude 55 degrees south.

In the past two years scientists have been using the high resolution camera on Mars Reconnaissance Orbiter (MRO) to monitor these scarps for changes. So far they have seen none, likely because the changes are below the resolution of the camera.

They have also been able to find more scarps in the southern hemisphere strip beyond that strip at 55 degrees south.

Now they have found more scarps in the northern hemisphere as well, and these are outside Milankovic Crater. As in the south, the new scarps are still all along a latitude strip at about 55 degrees.

The map above shows with the black dots the newer scarps located in the past two years. The scarp to the east of Milankovic Crater is typical of all the other scarps, a steep, pole-facing cliff that seems to be retreating away from the pole..

The scarp to the west of Milankovic Crater is striking in that it is actually a cluster of scarps, all inside a crater in the northern lowland plains. Moreover, these scarps are more indistinct, making them more difficult to identify. According to Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona,
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Ice! Ice! Everywhere on Mars ice!

Ice scarp in Milankovic Crater
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In January 2018 scientists announced the discovery of exposed ice in a number scarp cliff faces found in the high-mid-latitudes of Mars.

These scarps, which have so far been found in one southern 50-55 degree latitude strip and in one crater, Milankovic, at the same latitude in the north, are important because they are one of the first places on Mars in its lower latitudes where we have found ice actually exposed and visible, not buried like the many buried glaciers very near the surface found in the 30 to 60 degree northern and southern latitude bands.

Since that press announcement, scientists have been monitoring these sites for changes, as well as expanding their survey to see if they can locate more of these scarps.

Overview map

My previous posts on this subject were mostly focused on that southern strip near Hellas Basin, as shown on the map on the right. In reviewing the most recent image download from the high resolution camera on Mars Reconnaissance Orbiter (MRO), I noticed that the only new images of ice scarps were taken in the northern location, in Milankovic Crater, as indicated by the white dot north of Olympus Mons. The first image above shows the north-facing scarp of one of these images, cropped to focus in on the color section where, if you look close, you will see a strip of blue across the base of the scarp. That’s the ice layer, exposed as the scarp sublimates away over time from the north to the south.

over view of all MRO images taken so far in Milankovic Crater

This scarp, labeled #2 on the overview map of Milankovic Crater on the right, is located inside the crater’s eastern rim. The second image, posted below and labeled #1 on the overview map, shows a wider area of several ice scarps located on the inside of the crater’s southwestern rim.

The red boxes in the overview map indicate all the images taken by MRO inside this crater. If you go to the camera’s archive and focus in on Milankovic Crater at 54.5 degrees north latitude and 213.3 degrees longitude, you can then click on each red box to see the high resolution image. In practically every image along the crater’s inside rim can be found numerous scarps.
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The expanding range for Martian ice scarps

Another ice scarp
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The discovery in January 2018 of a number of Martian cliff faces, or scarps as the scientists dubbed them, with a visible and apparently very accessible underground layer of ice, had significant ramifications.

First, it proved that, in at least one area south of Hellas Basin and one spot in the northern hemisphere, an underground ice table existed on Mars at latitudes as far south as 55 degrees. Scientists had theorized that this ice table, comparable to the water table on Earth, existed, but here was visible proof.

Second, the discovery showed places where water could be accessed relatively easily by future colonists. There are plenty of indications from orbiter images and lander/rover data that water is present in many places on Mars, but here the water appeared almost pure and could be obtained without major digging or processing. Whether that ice table extends even farther south, making it even more accessible, remains as yet a scientific question.

In the next few months the scientists involved in this research located more ice scarps in areas beyond the range of those initial discoveries. Since then however even more scarps have been found, including the scarp in the image above and to the right, cropped, reduced, and annotated to post here.

This particular scarp is located inside a crater. The uncaptioned release from the high resolution camera on Mars Reconnaissance Orbiter (MRO), described it as a “Scarp in mantling material.” According to Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona,
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