[X] My Assistant

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With any luck the atmosphere will continue to warm and thicken as New Horizons makes its pass.

Thoughts?
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Pluto thought to be warming up

Astronomers at the University of Tasmania have found that the solar system's smallest planet is not getting colder as first thought and it probably does not have rings.

Dr John Greenhill has collected observations from last month's event when Pluto passed in front of a bright star, making it easier to study.

French scientists have shared the measurements they took in Tasmania that night, which indicate that the planet is unlikely to have rings.

Dr Greenhill says the results are surprising because they show Pluto is warming up.

"It looks as though the atmosphere has not changed from 2002, which is pretty surprising because we expected the atmosphere would freeze out as the planet moved further away from the Sun," he said.

"But so far, if anything, the atmosphere has gotten even denser."

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[hendric]

Also, Pluto's albedo isn't uniform, so is it possible that as it heads away from perihelion darker parts of the planet are preferred and keeping it warmer longer?

Also, I was wondering if the light/dark albedos could be a self-reinforcing effect? IE, the dark units stay warmer longer, preventing the atmosphere from condensing on them and lightening them up?

[JRehling]

Also, Pluto's albedo isn't uniform, so is it possible that as it heads away from perihelion darker parts of the planet are preferred and keeping it warmer longer?

Could be, although roughly speaking, Pluto has bright poles and a dark equator. You'd think that the equinox would provide maximum exposure of the dark areas, and that progressing towards a solstice would increase the explosure of bright, reflective pole surface. On the third hand ( ), that may defrost a pole out, increase the greenhouse effect, and/or decrease the albedo.

This is a complex dynamical system, and the increase in thickness now makes me a little nervous that there could be a sudden collapse before NH gets there. The more uphills you encounter before reaching your destination, the more downhills are waiting for you in the successive portions of your voyage. Of course, it may be a simple phase shift with the thermal seasons lagging behind the solar seasons.

Just to detail the Earth's continental climates as an example, St. Louis has a maximum average high sometime around July 22 (yes, this week) and low around January 12. Those average to a lag of about 25 days behind the solstice, or 6.8% of the year. The same proportion on Pluto (and there's no reason why it would be the same) would be 17 years. With an equinox at 1988, that would correspond to 2005, and lo, that's the same number Alan mentions and gibes with the sparse data showing that it's warmer in 2006 than 2002. If everything were symmetric, NH's arrival would be isothermal with 1995, and there was no freeze-out then.

[Guest_Richard Trigaux_*]

JRehling, Doug and Alan Stern, thermal inertia is a function of time, not of phase. And I would be very surprised that the small Pluto has a 17 year effect, when in is counted in days on Earth. In more, most of Earth's inertia is caused by the oceans, a very efficient retarder that Pluto don't have (nothing can remain liquid on Pluto surface). If Earth had a 248 years orbit, everything else the same, the lag would still be about 22 days, very far from 17 years.

So we cannot make a proportion in a matter of a fraction of the year (phase angle) but in absolute duration. So if we assume Pluto has the same inertia than earth, it is still 22 day, not 17 years. And even if some process would give a much larger inertia to Pluto than on Earth, 17 years make about four orders of magnitude more than Earth's ocean, I realy wonder what would store that much heat on Pluto than our oceans.

hendric, I think your idea of self reinforcing effect is interesting: dark places would be hotter, thus avoiding the condensation of gasses, while clear places would remain cold.

Eventually the evaporation of gasses could happen by bursts, suddenly cleaning a place from gasses and explaining surges in atmospheric pressure.

Big_Gazza, I still hold to the idea of geothermal heating. Of course Pluto is not Io, and even not Enceladus. But only a very small amount of geothermal heating would be enough to evaporate some frozen gasses in a pocket, in a time scale of centuries. It is much like geothermal melting of Antarctic ice cap, from the bottom, which is very weak, but on all the surface it is enough to form rivers. A geothermal flux as weak as we can imagine (due to a remnant or radioactivity, or tidal heating by the satellites) could, by accumulation over centuries or millenia, evaporate significant amounts of gasses, which could erupt violently, at times. The weaker the geothermal flux, the less eruptions, but the geothermal flux cannot be just zero.

[djellison]

Why do you suggest it wouldn't scale to be a longer duration effect with a longer duration orbit?

Doug

[Guest_Richard Trigaux_*]

Why do you suggest it wouldn't scale to be a longer duration effect with a longer duration orbit?

Doug

Simply because these two things have no relationship. The thermal inertia is the product of the energy necessary to heat a given mass of a body (massic heat), by the mass of this body. The orbit duration is a geometric consequence of the position of a planet in the solar system. Would the Earth be in the place of Pluto, it would still have the same thermal inertia (with a 22 day lag). So the lag would still be 22 day, not 17 years, and the phase angle would be much lower.


And I would be very surprised that the small pluto would have 40 times more thermal inertia than our large Earth. In more, the likely composition of pluto is bodies with a low massic heat, while earth has the largest know massic heat: water. (See The Messenger's post above)

[djellison]

Simply because these two things have no relationship. The thermal inertia is the product of the energy necessary to heat a given mass of a body (massic heat), by the mass of this body. The orbit duration is a geometric consequence of the position of a planet in the solar system. Would the Earth be in the place of Pluto, it would still have the same thermal inertia (with a 22 day lag). So the lag would still be 22 day

I disagree - you're imposing lag derived from a body at 1au through seasonal tilit over a cycle of 1 year, onto lag derived from orbital eccentricity at 30-50Au over 249 years. There's no grounds on which that is valid. I honestly can not understand why you think it is...there's no analogy between the two mechanisms nor the factors that deterime the range of values that derive from the two very different mechanisms.

Pluto will always be attempting to chase whatever would be an equilibrium temperature if it were to 'stop'

Why should Earth's behaviour have anything to do with that? It's a function of the orbital eccentricity, the thermal capacity of the planet itself, and it's ability to absorb heat. I can very very easily understand why that could result in a many year lag for a planet with such an eccentric orbit.

Doug