Tag: Mars

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Cool image time! The photo to the right, cropped and reduced to post here, is a great example of how a well known geological process on Earth, glaciers, can form features on Mars that appear most inexplicable.

The image was taken on May 13, 2020 and highlights the geology found in a depression, likely an eroded crater, on the northwest flanks of one of Mars’ largest basins, Argyre Planitia, located in the planet’s southern cratered highlands. The basin is thought to have been formed by a giant impact during the Late Heavy Bombardment around 3.9 billion years ago, when the inner terrestrial planets were sweeping up the last remnants of the Sun’s accretion disk, with that process causing the many craters we see on the Moon, Mercury, and Mars

This particular depression is at 41 degrees south latitude, in the mid-latitudes where scientists have found much evidence of buried glaciers. This is likely what we are looking at here. The section I’ve cropped has a dip to the south, which somewhat fits these flow features. If you look at the full image, you will see comparably weird flow features south of this section, flowing downhill in the opposite direction, to the north.

The problem is that not all the features fit the direction of flow, or any flow at all. I suspect we are seeing evidence of the waxing and waning of glaciers over this terrain over many eons. Disentangling that history however is confounding, especially when we are limited to only studying such objects from orbit.

I must also add that this image was labeled by the MRO science team a “terrain sample,” which means it wasn’t specifically requested by any scientist studying this geology. Instead, they needed to take an image to maintain the spacecraft’s camera temperature, and picked this spot for that snapshot. Their choice wasn’t random, but it also wasn’t based on any focused research.

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Cool image time! The image to the right, cropped and reduced to post here, was taken by Mars Reconnaissance Orbiter (MRO) on May 1, 2020, and shows a truly intriguing crater that they dub a “Crater Hanging on Mesa Wall.”

Located in Deuteronilus Mensae, a chaos region of mesas and cross-crossing canyons in the transition zone between the northern lowland plains and the southern cratered highlands, the crater literally overhangs the edge of this canyon’s cliff. The overview map to the right, with this location indicated by the red box, illustrates what this region’s geology is like.

The most likely explanation is that the impact occurred prior to the creation of the canyon, and when the canyon eroded, the material in and of this crater was more resistant, probably because the impact had packed it together to increase its density.

At the same time, the features inside both craters in the photo, as well as below them on the floor of the canyon, suggest the presence of buried glaciers, something not unlikely at the 45 degree north latitude where this crater sits.

So, here’s a guess at the geological history. First we had the impact, then during the eons of glacial ebb and flow on Mars due to wide swings in the planet’s obliquity (its rotational tilt), the canyon was cut, with that erosion leaving the crater sitting high above the canyon floor below it.

One more curious detail: The material in the canyon seems asymmetric, suggesting that the crater actually dips down toward the canyon, as if it as a unit has tilted to the east as the canyon was worn out below it.

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Cool image time! The photo to the right, cropped and reduced to post here, was taken on April 30, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Uncaptioned, the science team titled the release as a “Cataract in Osuga Valles.”

To understand what we are looking at it is necessary to also see a wider view, as provided by the context map below and to the right. As you can see, this image straddles across the canyon called Osuga Valles, and heads downstream to the east. It also shows a point where the grade of that canyon suddenly drops. If water ever flowed here this place would have been the location of a truly spectacular waterfall.

More likely, these cataracts mark the location where sometime in the past a glacier had flowed down this valley, cutting a path until it broke out into the large and wide dead end area that appears to have no clear outlet. For some reason at this point the downhill grade of this canyon suddenly dropped, with the glacier following that sudden steep drop.

There is no glaciers here now, as this location is at 14 degrees south latitude, too close to the equator for any ice to remain close to the surface. Instead, dust dunes remain as the only feature flowing down through these cataracts.

The second overview map provides further context, showing the location of Osuga Valles relative to nearby Valles Marineris, the largest known canyon system in the solar system. Whatever process formed that gigantic canyon system certainly was a factor in forming Osuga Valles. The details however are not yet understood with any certainty. All we presently have are theories.

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Cool image time! The photo to the right, cropped to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter on March 18, 2020. It shows a very strange central peak in a crater on Mars. Not only does this peak stick out like a sore thumb in a relatively flat crater floor, its surface is strangely textured, patterned with what look like scallops.

The overview map below shows the area covered in the crater by the full image.

My guess is that the peak is the final impact melt from the original impact. Think of a pebble thrown into a pond. You get ripples (the crater rim) as well as an upward drop of water (the central peak). Unlike pond water, the material in a crater freezes quickly, leaving both the ripple and the upward drop frozen in place.

This peak however also reminds me of volcanic cones found in the American southwest, the remnant cone of a much larger volcano that has long ago eroded away.

The textures might be evidence of that erosion process, as they resemble scallops that wind and water erosion can cause on rock faces.

We also could be seeing dunes on the slopes themselves, though I think this is unlikely. This crater is on the edge of the vast Medusae Fossae Formation, the largest volcanic ash deposit field on Mars, as shown by the white cross on the overview map below. Thus, being on the edge of this ash field there is a lot of available dust and sand that can pile up on these slopes.

Still, the sunlight side of the ridge suggests the scallops are in bedrock, not sand dunes. And to assign their origin to either wind or water or ice erosion I think is a stretch.

So while the peak is probably the frozen melt remains of the original impact, the scallops are a geological mystery that needs unraveling.

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Cool image time! The science team for the high resolution camera on Mars Reconnaissance Orbiter (MRO) today released a cool captioned image entitled “Exquisite Layering”, showing a place on the floor of Holden Crater where the dust and sand that normally covers most of the Martian surface has been wiped away, cleared off because these layers are on higher sloping terrain.

The image to the right, cropped to post here, focuses in on that exposed layering, believed to be sedimentary and must have therefore happened in the eons following the impact that caused the crater.

The overview map to the right shows with the red box the location of this layering inside Holden Crater. The map also illustrates why this crater was considered a candidate landing site for Curiosity. Like Gale Crater, it has evidence — the large meandering canyon system flowing into the crater — that suggests it had once been filled with a water lake. These sedimentary layers support that hypothesis, suggesting that this lake was intermittent. Each time it refilled and then dried up, it laid down a new deposit of those sedimentary layers.