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Dunes on the western edge of Arkhangelsky crater. Credit: Credit: NASA/JPL/University of Arizona


Craters and Dunes
Nov 19, 2010

Why are the bottoms of many craters on Mars filled with so-called "sand dunes"?

The atmospheric density on Mars is less than 1% that of Earth. It is composed almost entirely of carbon dioxide, although nitrogen and argon make up about 3%, with trace elements less than 1/10%. The temperature on Mars varies from a maximum of 20 Celsius to a minimum of -140 Celsius. The atmosphere is so thin that winds blowing at nearly 300 kilometers per hour exert almost no pressure.

Since the winds exert little force, what caused the formation of the many dune fields on Mars? Why do they also appear to be fresh looking and sharply delineated? Many of them are textured with fingerprint-like patterns or, as in the image at the top of the page, with scorch marks. In many cases, the dunes lie on top of quartz deposits that exhibit polygonal fracturing over a wide area.

Finding sand ripples or dunes on other planets incites the assumption that similar activity created what look to be the same kind of formations on Earth. Since sand and dust from wind and water erosion are presumed to have created the dune fields found here, then Mars "must have" had an environment at one time that provided the same conditions for them to form there.

Is projecting an Earth-like environment onto other worlds the right way to go? Should planetary scientists instead use the evidence from other worlds as a guide for what might have happened here?

Most sand dunes and ripples do not move around Mars. Some research has suggested that a small dune on Mars might take more than a thousand years to move a meter. Recent observations from the HiRise camera system do seem to show changes in some dunes, though, possibly due to the action of planet-wide dust storms, but the same press release announcing dune changes also states that some of them in other locations have not moved for 100,000 years.

The observed study area is within Nili Patera, Syrtis Major's so-called "collapsed lava pit." Syrtis Major is a mere nine degrees north of the Martian equator, a region that is sometimes swept by gigantic dust storms.

The Martian atmosphere is 100 times thinner than Earth and 75 degrees colder, on average. However, its dust storms are far larger than those seen on our planet and are accompanied by multi-kilometer high vortices, or "dust devils." When the Viking spacecraft landed on Mars, planetary scientists were surprised by all the suspended dust. They thought the sky would be dark, since the atmosphere is so thin that it should be too weak for small particles to blow around, let alone to raise such monstrous dust devils.

NASA scientists studied the dust devils in Arizona in order to understand what possible causes generate them on Mars. They discovered an electric field of up to 10,000 volts per meter associated with dust devils on Earth. This means that dust devils on both planets are an atmospheric electric discharge phenomenon similar to the electric winds produced by air ionizers. Perhaps it is ionic winds that are changing the shape of the dunes under consideration.

The dunes in Nili Patera are blackened, possibly due to the vast electric discharges that created them.

When electricity passes through a solid body, such as a planet, the current pulls charged material from the surface where the arc makes contact. Neutral dust and stones will be pulled along with the ionized particles as well. Craters formed by the arcs are most often circular because electromagnetic forces cause them to maintain right angles to the impact zone.

Since two or more filaments rotate around the arc axis, it can behave like a drill, excavating steep side walls and "pinching" a rolled rim. Often, the filaments will leave behind a central peak. Minerals in the crater will be electrically heated, scorched, and melted. This explains the scorch marks found on the Arkhangelsky crater dunes shown at the top of the page.

As Electric Universe proponent Wal Thornhill suggested, a positively charged surface will be melted, while the electromagnetic forces within the arc might lift the surface to form a "lightning blister,” called a fulgamite. Olympus Mons demonstrates the results of such a discharge: a gigantic mound with several overlapping craters at the top and a vertical drop off at its edge.

If the surface is negatively charged, an arc will travel, sometimes eroding elongated craters, like the enigmatic "boot-shaped" crater recently discussed in several press releases. The arc might also jump from high point to high point. Smaller craters on the rims of larger ones point to this phenomenon. A series of craters in a line, otherwise called a "crater chain," is another sign of arcing to a negatively charged substrate.

The advantage of the electrical interpretation is that it directly explains the nature of the topography dominating the craters on Mars. Electromagnetic forces between Birkeland currents constrained to a surface will force them into alignment. Ionic winds can lift material and carry it along in the direction of the current flow. Where a discharge channel bifurcates, the branches tend to remain parallel to each other and may rejoin. Orthogonal coronal discharges from parallel Birkeland currents generate the dune ripples.

It is most likely electrical effects that carved the craters on Mars and in so doing formed the drifts of finely pulverized debris that lie at their bottoms.

Stephen Smith


“The Thunderbolt that Raised Olympus Mons”



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