by neufer » Mon Jun 20, 2016 9:07 pm
Chris Peterson wrote:Guest2 wrote:
How can the UV be strong enough to cause significant reaction at that distance and temperature? Does not seem likely.
The temperature is largely irrelevant. And all the distance does is reduce the intensity, not the energy of the photons that cause the reactions. The reduced intensity simply means the reaction rate is reduced. The Sun at Pluto is about 1500 times fainter than it is at Earth. So figure, to a first approximation, that photolytic reactions will occur about 1500 times slower. In reality, the number is probably a lot smaller than this, since the Earth's atmosphere considerably reduces the amount of UV that makes it to the surface. So given Pluto's fairly stable surface and lack of significant weathering (except for space weathering), it's easy to understand how solar UV radiation can alter the surface, particularly over geological time spans.
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20150703-2 wrote:
<<What color is Pluto? The answer, revealed in the first maps made from New Horizons data, turns out to be shades of reddish brown.
Experts have long thought that reddish substances are generated as a particular color of ultraviolet light from the sun, called Lyman-alpha (UVC = 121.567 nm), strikes molecules of the gas methane (CH4) in Pluto's atmosphere, powering chemical reactions that create complex compounds called tholins.
The tholins drop to the ground to form a reddish "gunk."
Recent measurements with New Horizons' Alice instrument reveal that a diffuse Lyman-alpha glow falling on Pluto from all directions in interplanetary space is strong enough to produce almost as much tholin as the direct rays of the sun. "This means Pluto's reddening process occurs even on the night side where there's no sunlight, and in the depths of winter when the sun remains below the horizon for decades at a time," said New Horizons co-investigator Michael Summers, George Mason University, Fairfax, Virginia.>>
[quote="Chris Peterson"][quote="Guest2"]
How can the UV be strong enough to cause significant reaction at that distance and temperature? Does not seem likely.[/quote]
The temperature is largely irrelevant. And all the distance does is reduce the intensity, not the energy of the photons that cause the reactions. The reduced intensity simply means the reaction rate is reduced. The Sun at Pluto is about 1500 times fainter than it is at Earth. So figure, to a first approximation, that photolytic reactions will occur about 1500 times slower. In reality, the number is probably a lot smaller than this, since the Earth's atmosphere considerably reduces the amount of UV that makes it to the surface. So given Pluto's fairly stable surface and lack of significant weathering (except for space weathering), it's easy to understand how solar UV radiation can alter the surface, particularly over geological time spans.[/quote][quote=" http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20150703-2"]
[float=right][img3="[size=135][b][color=#BF00BF]All UVC is blocked by diatomic oxygen (from 100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in Earth's atmosphere.[/color]
[color=#00BF00]The ozone layer then blocks most UVB (from 280–315 nm).[/color][/b][/size]"]https://upload.wikimedia.org/wikipedia/commons/c/cb/Ozone_altitude_UV_graph.svg[/img3][/float]<<What color is Pluto? The answer, revealed in the first maps made from New Horizons data, turns out to be shades of reddish brown.
[b][color=#BF00BF]Experts have long thought that reddish substances are generated as a particular color of ultraviolet light from the sun, called Lyman-alpha (UVC = 121.567 nm), strikes molecules of the gas methane (CH[sub]4[/sub]) in Pluto's atmosphere[/color][/b], powering chemical reactions that create complex compounds called tholins. [url=https://en.wikipedia.org/wiki/Bartholomew_and_the_Oobleck]The tholins drop to the ground to form a reddish "gunk."[/url]
[b][u][color=#BF00BF]Recent measurements with New Horizons' Alice instrument reveal that a diffuse Lyman-alpha glow falling on Pluto [size=150]from all directions in interplanetary space[/size] is strong enough to produce almost as much tholin as the direct rays of the sun.[/color][/u][/b] "This means Pluto's reddening process occurs even on the night side where there's no sunlight, and in the depths of winter when the sun remains below the horizon for decades at a time," said New Horizons co-investigator Michael Summers, George Mason University, Fairfax, Virginia.>>[/quote]