by neufer » Sat Sep 26, 2015 1:34 pm
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.
It seems reasonable to assume that Pluto's ergs are geological remnants of
a past age of denser atmospheres & numerous cryovolcanic eruptions:
https://en.wikipedia.org/wiki/Triton_%28moon%29#Cryovolcanism wrote:
<<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.>>
[quote="OrionEridanus"][quote="Chris Peterson"]
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.[/quote]
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.[/quote]
[c]It seems reasonable to assume that Pluto's ergs are [b][u]geological remnants[/u][/b] of
a past age of denser atmospheres & numerous cryovolcanic eruptions:[/c]
[quote=" https://en.wikipedia.org/wiki/Triton_%28moon%29#Cryovolcanism"]
[float=right][img3="[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]"]https://upload.wikimedia.org/wikipedia/commons/5/58/Voyager_2_Triton_14bg_r90ccw_colorized.jpg[/img3][/float]<<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.>>[/quote]