Tag Archives: Martian North Pole

Watching the yearly vanishing of Mars’ north pole dry icecap

Buzzell dunes, March 19, 2019
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Buzzel dunes, April 4, 2019
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Buzzell dunes, June 4, 2019
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For the northern hemisphere of Mars it is presently spring. The season began sometime in April 2019 and will last until about October, twice as long as on Earth because of the Martian year is twice as long.

During the fall and winter the permanent water-icecap, which forms the bulk of the Martian icecap, gets covered by a mantle of dry ice, settling there as a layer of carbon dioxide snow about six feet thick. With the arrival of spring that dry icecap slowly begins sublimate away entirely.

Using the high resolution camera on Mars Reconnaissance Orbiter (MRO) planetary scientists are monitoring this process, taking pictures periodically.

On June 6, 2019 I had written a detailed story describing the Martian North Pole and outlining the process by which this sublimation of the dry icecap mantle takes place.

When winter ends and the sun reappears at this Arctic location, a small percentage of that sunlight, about 10%, goes through the dry ice and warms the sand that the dry ice mantles. This in turn warms the bottom of the dry ice layer, causing this to sublimate into a gas that is now trapped.

When the pressure builds sufficiently, that gas breaks free at the weakest spots in the dry ice layer, which are either at the dune crest or at its base, or sometimes on its face where cracks form. When it does so the CO2 gas carries with it material from below, which appears dark relative to the bright dry ice on the surface. As the summer season progresses and more dry ice sublimates away, the dark smudges disappear as they slowly blend in with the now-exposed original sand surface.

The first two pictures to the right were posted in that June 6, 2019 story, showing the initial evidence of sublimation on a set of dunes that the scientists have dubbed Buzzell. Below these, I have now added the newest image of the Buzzell dunes, taken on June 4, 2019 and just released in the August MRO image dump.

When this third image was taken, spring was only about two months old. Yet, this sublimation process is clearly accelerating. You can see many more dark patches at the crests and bases of many dunes, especially in the upper left of the image. According to Dr. Candice Hansen of the Planetary Science Institute in Tucson, Arizona, who is requesting these monitoring images, by sometime in October “you’ll see how the entire spring progresses from dunes completely covered with dry ice to the summer when they are just bare sand. Then you could comment on the whole spring series.”

I fully intend to do this. No harm however in providing an interim report or two. Stay tuned to Behind the Black for future on-going and up-to-date reports on the shrinking north pole dry icecap of Mars!

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The Martian North Pole

The Martian North Pole

Since the very beginning of telescopic astronomy, the Martian poles have fascinated. Their changing sizes as the seasons progressed suggested to the early astronomers that Mars might be similar to Earth. Since the advent of the space age we have learned that no, Mars is not similar to Earth, and that its poles only resemble Earth’s in a very superficial way.

Yet, understanding the geology and seasonal evolution of the Martian poles is critical to understanding the planet itself.

This post will focus on the Martian north pole. The map on the right of the north polar regions is based on many satellite images supplemented by a lot of research by planetary scientists. The black circle in the middle is an area with relatively poor image coverage. The green areas are regions of higher elevation where the bulk of the permanent ice cap is located, surrounded by the blue northern lowlands that cover much of Mars’s northern hemisphere and are thought to have once harbored an intermittent ocean.

Olympia Undae dune field
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The reddish regions encircling the permanent ice cap are large seas of sand dunes, with Olympia Undae the largest and most sand-dune-packed. The image on the right, posted initially here on March 25, 2016, was taken by Mars Odyssey and shows the endlessness of this dune sea. Olympia Undae, spanning 120 degrees of longitude, is about 700 miles long, making it bigger than the Grand Canyon. As I noted in that post, “Just imagine trying to travel though this area. It is the epitome of a trackless waste. And without some form of GPS system getting lost forever would be incredibly easy.”

The polar cap itself, surrounded by those sand seas, is 600 miles across and a little less than 7,000 feet deep. It is made up of many seasonal layers, like the icecaps on Earth, with the bulk a mixture of water ice and cemented dust and sand. The very top layers, dubbed the residual icecap, is about three to six feet thick made up of frozen water having a volume about half of Greenland’s icecap. While this water could evaporate away, data suggests it is, like the icecaps on Earth, in a steady state, neither gaining or losing volume with each Martian year.

Above the residual icecap of water is the seasonal icecap made up of carbon dioxide. Unlike the other layers, this seasonal cap of dry ice, also less than six feet thick, comes and goes with the seasons. During the Martian summer it is gone, the carbon dioxide having sublimated away into the atmosphere. As the weather chills however that carbon dioxide begins to freeze again, falling as CO2 snow on the surface at the poles to create a thin cap of dry ice extending down to about 60 degrees latitude and covering practically everything seen in the first map above.

These facts suggest that future Martian colonists will have an interest in this region. While harsher than the rest of the planet, the conditions at the poles are not so much different that it will be impossible to work here. And here they will find a ready supply of carbon dioxide to help their plants grow, as well as a ready supply of water, all easily mined and near the surface.

In order to understand how this dry ice cap comes and goes, scientists have been using the high resolution camera of Mars Reconnaissance Orbiter (MRO) to repeatedly monitor some of the same locations in these sand seas to track the seasonal changes. In my routine review of the new images downloaded from MRO in May, I came across more than a dozen such images, all of which had been requested by Dr. Candice Hansen of the Planetary Science Institute in Tucson, Arizona, and taken just as the Martian winter was ending and spring was beginning. As she explained to me, “The images I’m requesting now follow-up on many of our earlier study sites so that we can study interannual variability. We’re also looking at more places to get a sense of what is similar/different depending on where you are.”

Below are two of these recent images, showing one example of the springtime changes that can be seen on these dunes.
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