Starship Asterisk*

http://earthobservatory.nasa.gov/IOTD/view.php?id=6910 wrote:

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[b][color=#0000FF][size=125]Astronaut photograph ISS013-E-65526 was acquired August 8, 2006, with a Kodak 760C digital camera with an 800 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast.[/size][/color][/b]

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Dune Types in the Issaouane Erg, Eastern Algeria
Earth Observatory, September 11, 2006

<<This view from one of the smaller dune seas in the central Sahara Desert shows the complex but regular patterns produced in deserts where wind and sand both abound. The image is centered at 26.9 North, 7.4 East, over eastern Algeria. Geologists now know that dune seas (also called ergs) exhibit at least three orders of dune size. The biggest dunes, called mega-dunes, probably took hundreds of thousands of years to accumulate, starting when the Sahara began turning arid roughly 2.5 million years ago. Rivers became smaller, failed to reach the sea, and deposited their sand load in the desert. Wind did the rest, blowing the sand into aerodynamic dune forms. Superimposed on the mega-dunes are mesoscale dunes (the prefix meso- means “intermediate.”) Whereas the mega-dunes are apparently stationary, studies based on aerial photographs in other parts of the world show that mesoscale dune crests move in the course of decades. The smallest dunes form and reform the fastest, meandering over the backs of the larger dunes.

In this image, the mega-dunes appear as big, rolling lumps that zigzag toward the upper right. The “streets” between these biggest dune chains have been swept clean of sand in places, showing their original surfaces of pale mud and salts. The pale beige-grey of these areas contrasts with the otherwise burnt orange hues. Mesoscale dunes, some of which form octopus-like crests, or star dunes, mark the backs of the mega-dunes. The smallest dunes appear in patches on the eastern sides of the mega-dunes as a tracery of closely spaced crests. Interestingly, the crest orientation of the small dunes differs from the orientation of the mesoscale dunes. This difference is a common effect of local shifts in wind direction, which is influenced by dune height.

The orientation trends in the mega-dunes coincide with two of the four major trends identified in the Great Eastern Sand Sea (or Grand Erg Oriental) immediately to the north. Each orientation shift likely implies a shift in the direction of the dominant wind that formed the dunes, attesting to the climate shifts that have occurred since sand began to accumulate in the central Sahara.>>

stolenmoment wrote:The area at the right edge looks more like a layer of fluff blown across a much flatter surface.

captainwiggins48 wrote:
The seemingly sculpted landscape of Pluto may have been caused by past supernova events
of nearby stars, and/or events from our own sun, all nicely preserved for us to ponder.

MarkBour wrote:When the caption says: "resolves details on the distant world about 1.3 kilometers (0.8 miles) across.", is this a subjective statement, or can it be translated into something more specific, such as "each pixel is 1.3 km"?

At the scale these may be, and with the likelihood that the atmosphere of Pluto has always been super-thin, I am doubtful that wind played much of a role in forming these structures.

MarkBour wrote:
When the caption says: "resolves details on the distant world about 1.3 kilometers (0.8 miles) across.", is this a subjective statement, or can it be translated into something more specific, such as "each pixel is 1.3 km"? I'd be interested in knowing that.

http://www.planetary.org/blogs/emily-lakdawalla/2015/09241425-lose-yourself-in-this-pluto.html wrote:
Lose yourself in this high-resolution portrait of Pluto
Posted By Emily Lakdawalla

<<[New Horizons team member Alex Parker] confirmed that the image had been upsampled (enlarged) by a factor of 2 as a part of his deconvolution process. I'm oversimplifying here, but deconvolution is a step in image processing where you account for the fact that your detector has an inherent blur. Before you send a scientific camera to space, you perform a lot of tests on it to understand very precisely the geometry of that blur. With an excellent model of its geometry, you can take the blur out, sharpening the images in a way that is very specific to your precise understanding of your scientific camera.>>

MarkBour wrote:
<<It would be helpful for the scale to compare this image to a shot of some of the worst badlands on Earth at the same scale. At the scale these may be, and with the likelihood that the atmosphere of Pluto has always been super-thin, I am doubtful that wind played much of a role in forming these structures.>>

MarkBour wrote:When the caption says: "resolves details on the distant world about 1.3 kilometers (0.8 miles) across.", is this a subjective statement, or can it be translated into something more specific, such as "each pixel is 1.3 km"? I'd be interested in knowing that. It would be helpful for the scale to compare this image to a shot of some of the worst badlands on Earth at the same scale. At the scale these may be, and with the likelihood that the atmosphere of Pluto has always been super-thin, I am doubtful that wind played much of a role in forming these structures.

ta152h0 wrote:
So on Pluto they be called " dwarf ergs " ?

https://en.wikipedia.org/wiki/Erg_%28landform%29 wrote:
<<An erg is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover. The term takes its name from the Arabic word ʿarq (عرق), meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than 125 square kilometres of aeolian or wind-blown sand and where sand covers more than 20% of the surface. Smaller areas are known as "dune fields". The largest hot desert in the world, the Sahara, covers 9 million square kilometres and contains several ergs. Ergs are also found on other celestial bodies, such as Venus, Mars, and Saturn's moon Titan.>>

https://en.wikipedia.org/wiki/Hyperion_Cantos wrote:
<<The Hyperion Cantos is a series of science fiction novels by Dan Simmons. Much of the action in the series takes place on the planet Hyperion. It is described as having one-fifth less gravity than Earth[; Pluto has 1/16 g]. Hyperion has a number of peculiar indigenous flora and fauna, notably Tesla trees, which are essentially large electricity-spewing trees.

Hyperion is also a "labyrinthine" planet, which means that it is home to ancient subterranean labyrinths of unknown purpose. Most importantly, Hyperion is the location of the Time Tombs, large artifacts surrounded by "anti-entropic" fields that allow them to move backward through time.>>

Chris Peterson wrote:

. On the other hand, with such a tenuous atmosphere (which implies very low mass density) you could have winds with incredible speeds- hundreds or even thousands of kilometers per hour. And any "snow" that precipitates is likely to be little more than small clumps of molecules. Under such conditions, I'd be hesitant to say that wind might not be very important in shaping the landscape.

OrionEridanus wrote:

Chris Peterson wrote:
On the other hand, with such a tenuous atmosphere (which implies very low mass density) you could have winds with incredible speeds- hundreds or even thousands of kilometers per hour. And any "snow" that precipitates is likely to be little more than small clumps of molecules. Under such conditions, I'd be hesitant to say that wind might not be very important in shaping the landscape.

Windspeed cannot exceed the speed of the sound which is solely dependent on temperature and particle mass. If it did the "wind" becomes a shock wave with all the gas piling up on the shock boundary rather than propagating as a pressure driven flow.

https://en.wikipedia.org/wiki/Triton_%28moon%29#Cryovolcanism wrote:

[b][color=#0000FF][size=125]Dark streaks across Triton's south polar cap surface, thought to be dust deposits left by eruptions of nitrogen geysers[/size][/color][/b]

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<<Triton is geologically active; its surface is young and has relatively few impact craters. Although Triton is made of various ices, its subsurface processes are similar to those that produce volcanoes and rift valleys on Earth, but with water and ammonia lavas as opposed to liquid rock. Triton's entire surface is cut by complex valleys and ridges, probably the result of tectonics and icy volcanism. The vast majority of surface features on Triton are endogenic—the result of internal geological processes rather than external processes such as impacts. Most are volcanic and extrusive in nature, rather than tectonic.

The Voyager 2 probe observed a handful of geyser-like eruptions of invisible nitrogen gas and entrained dust from beneath the surface of Triton in plumes up to 8 km high. Triton is thus, along with Earth, Io, and Enceladus, one of the few bodies in the Solar System on which active eruptions of some sort have been observed.

All the geysers observed were located between 50° and 57°S, the part of Triton's surface close to the subsolar point. This indicates that solar heating, although very weak at Triton's great distance from the Sun, plays a crucial role. It is thought that the surface of Triton probably consists of a translucent layer of frozen nitrogen overlying a darker substrate, which creates a kind of "solid greenhouse effect". Solar radiation passes through the surface ice, slowly heating and vaporizing subsurface nitrogen until enough gas pressure accumulates for it to erupt through the crust. A temperature increase of just 4 K above the ambient surface temperature of 37 K could drive eruptions to the heights observed. Although commonly termed "cryovolcanic", this nitrogen plume activity is distinct from Triton's larger scale cryovolcanic eruptions, as well as volcanic processes on other worlds, which are powered by the internal heat of the body in question. Analogous CO2 geysers on Mars are thought to erupt from its south polar cap each spring.

Each eruption of a Triton geyser may last up to a year, driven by the sublimation of about 100 million cubic metres of nitrogen ice over this interval; dust entrained may be deposited up to 150 km downwind in visible streaks, and perhaps much farther in more diffuse deposits. Voyager 2‍‍ '​‍s images of Triton's southern hemisphere show many such streaks of dark material. Between 1977 and the Voyager 2 flyby in 1989, Triton shifted from a reddish colour, similar to Pluto, to a far paler hue, suggesting that lighter nitrogen frosts had covered older reddish material. The eruption of volatiles from Triton's equator and their deposition at the poles may redistribute enough mass over the course of 10,000 years to cause polar wander.>>