A Sandy Sea

Sand dunes and yardangs on Titan. Credit: NASA/JPL-Caltech/ASI/ESA. Click to enlarge.


Mar 29, 2017

Giant dune formations are found on Titan.

A previous Picture of the Day noted that there is no flowing liquid on Saturn’s moon, Titan, and that the so-called “river valleys” discovered by the Cassini orbiter are probably the remains of electric discharge effects. Electric Universe advocates predicted at the time of discovery that the rilles would ignore the topography, traveling uphill as well as downhill—nothing like a moving stream.

“Sinuous rilles” occur on most rocky planets and moons. Although they superficially resemble river systems on Earth, there are no catchment areas or feeder streams and the tributaries are short, often meeting the main channel at right angles. Also, the flat depressions on Titan could have been etched out by energetic plasma discharges.

Titan is an electrically charged body: there is a particle fountain flowing out of its poles and a torus of charged particles encircling it. Streams of charged particles are circling Titan in the same way that electrons and positive ions circle Earth in opposite directions: a plasma ring surrounds Titan, influencing its geology and its weather.

A recent press release announced that the large deposits of sand on Titan are “electrically charged”, which is why they can move around the moon and collect in vast dune fields. Titan’s average wind speed is less than 20 kilometers per hour, so the accumulation of sand into drifts 100 meters high is hard to explain. The dunes also appear to be entrained, with no evidence for movement over the years.

Quoting from the article:

“Titan’s extreme physical environment requires scientists to think differently about what we’ve learned of Earth’s granular dynamics. Landforms are influenced by forces that aren’t intuitive to us because those forces aren’t so important on Earth. Titan is a strange, electrostatically sticky world.”

Dunes are found in four places: Earth, Mars, Venus, and Titan. On Earth, the average temperature is approximately 16 Celsius, with plenty of liquid water. On Mars, the average temperature is minus 50 Celsius with no liquid water at all. While Venus, a scalded lava planet, averages 460 Celsius. The surface temperature on Titan averages minus 180 Celsius. It is so cold that water is like rock, so it does not contribute to any chemistry. What creates heaps of particles, some hundreds of meters high, despite the disparity in environments?

On Titan, the dunes are well-defined, almost solid-looking waves, that bury craters and surround large “yardangs”. They follow the prevailing wind pattern, but they also have some unusual characteristics that may mean they are not generated by wind in the conventional sense. Many of them look like fingerprint patterns that are crisscrossed by other ripples, similar to dune fields found along the coast of Namibia.

Sand grains and dust must be able to slide freely over one another for dunes to pile up and move. Strong winds are usually required to move the sand. In some places, sand dunes cover thousands of square kilometers, but they are fossilized and immobile. Whenever the sand appeared, it was never able to move again, so the dunes are crusted over, providing shelter for plants and animals.

When the Huygens probe landed on Titan, it sank slightly into a friable surface. NASA described it alternately as “wet snow”, “loose clay”, or “dry sand”. There was some detectable methane in the area surrounding the probe, but it quickly dissipated—presumably because of the lander’s heat. Mission specialists believe that Titan is covered in liquid methane. However, if Titan is wet, the winds would not be able to consolidate material. With such minimal wind speeds, it stands to reason that Titan is dry, despite claims from NASA that there are “lakes” of liquid ethane and methane on its surface.

There are craters on Titan, with folded rims and flat bottoms, or concentric basins. Parallel fractures and large domes are similar to those on Venus, while Lichtenberg figures (called river channels by the Cassini team) are seen cut into the terrain. A better explanation for what happened to Saturn’s planet-sized moon might be found by considering Mars.

On Mars, dunes are identified with electric arcs that blew the sand upward along the path of charge flow. It then fell away, forming what planetary scientists call, “wind streaks.” Dust most likely carries electric charge on Mars, so particles are attracted or repelled from one another, depending on their polarity. Therefore, they align in the same way that iron filings align with a magnetic field. It is possible that that is the mechanism behind the dune structures on Titan, as well.

Stephen Smith

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