Pluto Atmospheric Observations: NH Post-Encounter Phase, 1 Aug 2015- TBD Options

[scalbers]

A neat paper by Jonathan Fortney shows this ratio to scale (approximately) with sqrt(Rp/H), with Rp being the planet radius and H the scale height. Both indeed decrease this effect for Pluto.

If we assume the scale height of Pluto's atmosphere is 60km and the aerosols have the same height as the gas, then I was able to get a few numbers in the course of comparing various airmass equations. Earth would be about 39 airmasses in the horizontal and Pluto would be 6.4. These numbers would be doubled when looking at grazing incidence from space as in the NH images. I'd still like to come up with a formula for an isothermal atmosphere (exponential density decrease with height) by integrating the thin shell relationship over height and to compare this with the other formulations in Wikipedia. On the other hand, the isothermal case is within just a few percent of the homogeneous (constant density with height) case.

To check the scale height and see why it is much higher than Earth, we might evaluate this expression for Earth and Pluto:

H = kT/mg

H is scale height
T is temperature (a representative value since this varies with height)
k is Boltzmann's constant
m is molecular mass
g is gravitational acceleration

The Wikipedia link above shows this worked example for Earth:

Taking T = 288.15 K, k = 1.3806488x10-13 J/K, m = 28.9644×1.6605×10−27 kg, and g = 9.80665 m/s2 yields H = 8345m

Roughly speaking, if pluto has .07 Earth's gravity and the same T and similar m we'd get about 120km scale height. If the scale height is 60km, then the temperature would still end up being ~140K. So we can check how much the temperature increases with height over the surface value of 44K.

There are other atmosphere posts in the Near Encounter thread as well (e.g. posts #1238 and #1252).

[Sherbert]

The general conclusion seems to be that Pluto's "sky" would be "space" during the day, but near sunrise and sunset the "haze" of the atmosphere should be discernible. That would be something to see, two "night skies" in one day.

This being the case would "shooting stars" be visible? That is, is the atmosphere "thick" enough to "burn up" incoming debris? Its not very dense, but it is "tall".

Whether visible or not, not all the atmosphere comes from the surface ices. Icy objects entering the atmosphere and "evaporating" could add significantly to Pluto's atmosphere over time. Its not going to replace 500 tonnes per hour thats for sure, but might help maintain the atmosphere's depth and seed ice crystals, via dust and organics, at higher levels of the atmosphere than those materials being transported from the surface reach. Pluto's equivalent of Noctilucent clouds. One might expect atmospheric dynamics would mix the two, but it is very cold and the evidence is that there are distinct layers within the atmosphere.

[Herobrine]

This being the case would "shooting stars" be visible? That is, is the atmosphere "thick" enough to "burn up" incoming debris? Its not very dense, but it is "tall".

Not having done any calculations, personally, I'd be surprised if you could ever get a visible "shooting star" at Pluto. I suppose it wouldn't be too terribly difficult to calculate approximations of how hot/bright a large, stony meteor would get, crossing through the densest part of Pluto's atmosphere at 100,000 m/s or something. I just can't imagine it's enough to generate the heat required for it to become visible to the human eye, even as sensitive as that is.
I remember reading about a meteor believed to have been imaged by one of the Mars rovers, but while Mars' atmosphere is something like 1/100th as dense as Earth's, Pluto's is like a thousand times less dense than that.
If someone does the math and it suggests it's possible, I'll believe it, but in my mind, Pluto's atmosphere is so thin, you could scoop it away at 1,000 km/s with a nix-sized scoop without generating enough heat to really glow.
^{I'm frequently wrong, though.}

[JRehling]

Meteors may appear over Earth at altitudes where the pressure is less than the maximum surface pressure on Pluto, which suggests that visible meteors could be possible (were there anyone there to see them). However, recall that the velocity of meteors running into Pluto should be much less than the velocity of meteors hitting Earth's upper atmosphere. However: Water ice wouldn't remain ice when it was hot enough to glow, and would soon be a puff of vapor.

So, a visible meteor on Pluto would require an anomalously high velocity, and for the speck to be silicate rather than ice. I'll bet it's happened, but rarely.