Behind The Black – Robert Zimmerman

Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 27, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a small section of the floor and northern slope of Hebes Chasma, one of the many very large enclosed pits that can be found to the north of Valles Marineris, the largest canyon in the solar system. Though Hebes seems small next to the 1,500 mile long Valles Marineris, it still is 200 miles long by 80 miles wide, and could easily fit a half dozen Grand Canyons within it.

For example, the Grand Canyon is from 4,420 to 5,400 feet deep, hiking down from the south and north rim lodges respectively, which sit about ten miles apart. On this picture, the peak on the right sits about 5,300 feet above and only about 3.8 miles from the low spot on the bottom left, which means this one small picture encapsulates the Grand Canyon. And yet, the northern rim of Hebes sits another 21,000 feet higher and twelve miles away. And the entire chasma itself extends 50 miles to the west, 150 miles to the east, and 50 miles to the south.
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Today’s cool image will be a mystery with the answer below the fold. Before you look at the answer, however, you must try to come up with your own explanation for the picture to the right, cropped to post here, that was taken on September 25, 2018 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

What we see in this picture is what looks like a striped terrain, alternating bands of light and dark. What caused the bands? Why the different colors?

The overview map above provides some clues. The white rectangle inside Juventae Chasma near the map’s center marks the area within which this picture was taken, though the picture to the right covers only about a pixel inside that rectangle.

Can you guess what these stripes reveal, from this little information? For this quiz to work you must make a guess, but be prepared to be wrong and quickly reassess your conclusions. Such is the real scientific method, so rarely taught now in schools.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on September 19, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The features are described as “ribbed terrain” in the label. To my eye they more resemble flakes of peeling paint, most especially the mesas in the lower left. On the full image there are many more examples that resemble old paint peels, barely attached to the wall.

The white dot on the overview map above marks the location, deep inside the 2,000-mile-long strip in the northern mid-latitudes I dub glacier country, because everything seems covered by glacial features. This location is at 42 degrees north latitude, where plenty of near-surface ice features are found on Mars.

At first glance it looks like the top “paint-peel” layers to the south have been slowly sublimating away, leaving behind the smooth plain to the north. The problem is that this smooth area in the full image actually appears to be a glacial ice sheet of its own, filling all the low areas between mesas.

In other words, we are probably looking at layers and layers of ice sheets, each created during a different Martian climate cycle, caused by the wide swings of the planet’s rotational tilt, or obliquity.

The location is within Arabia Terra, the largest transitional zone on Mars between the northern lowland plains and the southern cratered highlands. Thus it sits above the glaciers that fill the lower regions of chaos to the north. What we have here is terrain that will eventually become chaos terrain, as the narrow faults and cracks are slowly widened into canyons by the cycles of glacial activity.

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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on May 28, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The picture label describes it as a “Low Shield Vent and Pit Northeast of Arsia Mons,” suggesting these depressions are volcanic in nature. We know the pit in the lower left is not an impact crater because it has no raised rim of ejecta. Instead, it looks like a collapsed sinkhole, formed when the ceiling above a void could no longer support its weight. Similar, the trench to the northeast is aligned with the downhill grade to the northeast, with its features suggesting a vent draining in that direction.

The ample dust inside the trench and pit suggest that it has been a very long time since this vent was active. Research suggests volcanic activity last occurred in this region from 10 to 300 million years ago, so that gives us a rough estimate of this vent’s age. Since then any dust that is blown into it will tend to become trapped there.
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