With any luck the atmosphere will continue to warm and thicken as New Horizons makes its pass.
Thoughts?
_______
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."
abc
Full Version: Is Pluto warming up?
QUOTE (ups @ Jul 26 2006, 03:15 PM) 
With any luck the atmosphere will continue to warm and thicken as New Horizons makes its pass.
Thoughts?
Thoughts?
Thanks, ups. This is interesting, though I'd be interested in seeing exactly what Greenhill et al. are claiming and, moreover, what they manage to get through peer review.
That said, it's probably good that this press release didn't come out before New Horizons was launched.
Ah, global warming extending to Pluto, even Greepeace did not expected that 
The curious thing is that the atmosphere seems denser when they expected it would become lighter, from increasing cold. This is perhaps from some cryovolcanic activity. We can imagine a surface layer of frozen volatiles, which would warm up from bottom by geothermal heating. At moments, deep pockets of gasses would erupt to the surface, thickening the atmosphere. And then, they would freeze again, forming surface layers. So the overal frozen gas layer would slowly turn over itself.
The curious thing is that the atmosphere seems denser when they expected it would become lighter, from increasing cold. This is perhaps from some cryovolcanic activity. We can imagine a surface layer of frozen volatiles, which would warm up from bottom by geothermal heating. At moments, deep pockets of gasses would erupt to the surface, thickening the atmosphere. And then, they would freeze again, forming surface layers. So the overal frozen gas layer would slowly turn over itself.
QUOTE (Richard Trigaux @ Jul 27 2006, 04:47 PM)
Ah, global warming extending to Pluto, even Greepeace did not expected that
The curious thing is that the atmosphere seems denser when they expected it would become lighter, from increasing cold. This is perhaps from some cryovolcanic activity. We can imagine a surface layer of frozen volatiles, which would warm up from bottom by geothermal heating. At moments, deep pockets of gasses would erupt to the surface, thickening the atmosphere. And then, they would freeze again, forming surface layers. So the overal frozen gas layer would slowly turn over itself.
The curious thing is that the atmosphere seems denser when they expected it would become lighter, from increasing cold. This is perhaps from some cryovolcanic activity. We can imagine a surface layer of frozen volatiles, which would warm up from bottom by geothermal heating. At moments, deep pockets of gasses would erupt to the surface, thickening the atmosphere. And then, they would freeze again, forming surface layers. So the overal frozen gas layer would slowly turn over itself.
Geothermal heating? In a small icy body 40AU from the sun? Unlike Europa, Enceladus or Triton, Pluto is not in orbit around a large parent capable of invoking tidal forces, and any heat from radioactive decay in its rocky core would be insufficient to drive any appreciable activity. Charon no doubt contributes some tidal heating, but it would surely be negligible.
Having said that, the HST images show striking albedo variations, so clearly the surface demonstrates variety. I expect that we will see evidence of past geological activity, but long since ceased, and of course the expected seasonal frosts waxing & waning with orbital distance.
Can't wait for NH to arrive!!
Lets hope Pluto is more than a distant cousin of boring Rhea! That would be a cause for much grief and a gnashing of teeth 
I'll still put my money on it being a simple case of thermal inertia, i.e., a phase delay between
perihelion and the warmest day. Almost 20 years ago we modelled this effect in a paper
led by Larry Trafton and predcted phase lags of up to 17 years after perihelion (1989.7)
before the cooling begins. The situation is rather anlagous to the reason the hottest days of
summer are some weeks after the summer solstice, but Pluto's 248 year orbital timescale stretches
everything out from weeks to decades.
perihelion and the warmest day. Almost 20 years ago we modelled this effect in a paper
led by Larry Trafton and predcted phase lags of up to 17 years after perihelion (1989.7)
before the cooling begins. The situation is rather anlagous to the reason the hottest days of
summer are some weeks after the summer solstice, but Pluto's 248 year orbital timescale stretches
everything out from weeks to decades.
You beat me to it, Alan, but that was my feeling as well.
Phil
Phil
Just out of interest...I set up a spreadsheet..
All units are just random really - I set up a body with a thermal capacity which was added to at a rate that followed the inverse square of an orbit from 90 to 110 random units..but that energy was lost at a constant rate
The attached shows the 'range' to the sun in blue, and the 'temperature' of the body in pink - and it lags behind the range by quite a bit. I probably screwed up the maths somewhere, but it showed that 'thermal lag' of an object behind the seasonal temperature.
All units are just random really - I set up a body with a thermal capacity which was added to at a rate that followed the inverse square of an orbit from 90 to 110 random units..but that energy was lost at a constant rate
The attached shows the 'range' to the sun in blue, and the 'temperature' of the body in pink - and it lags behind the range by quite a bit. I probably screwed up the maths somewhere, but it showed that 'thermal lag' of an object behind the seasonal temperature.
QUOTE (Big_Gazza @ Jul 27 2006, 05:34 AM)
Charon no doubt contributes some tidal heating, but it would surely be negligible.
Actually, it wouldn't. Pluto and Charon both keep the same face towards the other all of the time, so there wouldn't be any tides in the system at all. With nothing to force Charon's orbit, it would circularize and then stay like that for eons.
On second thought, I've forgotten for the moment about Nyx and Hydra. They'd contribute some tidal action, partly from their own gravity acting on Pluto, and partly from keeping Charon's orbit a bit elliptical (assuming they are in resonance with Charon). But geez, it couldn't amount to much.
As for thermal inertia, methane's a pretty strong greenhouse gas, isn't it?
QUOTE (Alan Stern @ Jul 27 2006, 01:54 AM)
I'll still put my money on it being a simple case of thermal inertia, i.e., a phase delay between
perihelion and the warmest day. Almost 20 years ago we modelled this effect in a paper
led by Larry Trafton and predcted phase lags of up to 17 years after perihelion (1989.7)
before the cooling begins. The situation is rather anlagous to the reason the hottest days of
summer are some weeks after the summer solstice, but Pluto's 248 year orbital timescale stretches
everything out from weeks to decades.
perihelion and the warmest day. Almost 20 years ago we modelled this effect in a paper
led by Larry Trafton and predcted phase lags of up to 17 years after perihelion (1989.7)
before the cooling begins. The situation is rather anlagous to the reason the hottest days of
summer are some weeks after the summer solstice, but Pluto's 248 year orbital timescale stretches
everything out from weeks to decades.
Alan, I'm not sure if you were aboard at the time but other Yahoo! planetary_sciences alumni may recall a rather long thread "The Plutonian Atmospheric Collapse Debate" from 2002, which I started at message #3960. I'll quote that post below verbatim and without any editing, which means I'll probably be embarrassed
Oh, and don't assume the four-year old links still work.QUOTEWell, I just had the chance to re-read:
Emissivity and the Fate of Pluto's Atmosphere
J. A. Stansberry and R. V. Yelle
Icarus Vol. 141, No. 2, October 1, 1999, pp. 299-306
(doi:10.1006/icar.1999.6169)
Abstract http://www.idealibrary.com/links/doi/10.1006/icar.1999.6169
which was offered as support for the recent AAS/DPS press release,
which, while endorsing New Horizons, downplayed the significance of
the criticality of meeting the 2006 JGA launch window in order to
arrive before Pluto's predicted atmospheric collapse. As Bruce noted
in his recent SpaceDaily piece, the DPS's position in this regard is
a minority one; the Pluto SDT and the planetary sciences community at
large have identified Plutonian atmospheric studies *before* collapse
as a Group 1 science objective (i.e., one that is integral to the
mission's justification). However, Stansberry and Yelle [1999] offer
a different view of the predicted Plutonian atmospheric collapse, one
that is at odds with the prevailing one. As the abstract to their
paper indicates, their model is based on "... the potential
importance of the solid-state phase transition between [alpha-
nitrogen] a-N2 and [beta-nitrogen] B-N2 ... [and] shows that under
simplified but not unreasonable assumptions Pluto may have nearly the
same atmospheric pressure at aphelion as it does now, near
perihelion." In other words, no freezing out. At the outset,
Stansberry and Yelle's model assumes that the nitrogen ice on Pluto's
surface has a globally uniform temperature (i.e., is isothermal),
which they label T(N2), or at least does not vary "within a small
fraction of a Kelvin." They base this assumption on the efficiency
in common volatile/energy redistribution processes (e.g.,
sublimation, condensation, atmospheric transport, etc.), which the
presume does not alter the overall energy balance. To this end, they
utilize theoretical models and laboratory studies of the nitrogen a-B
phase transition, which occurs at a temperature (TaB) of 35.6 K, and
note the "sudden change" (or contrast) observed in bolometric
emissivity (thermal reradiation) at TaB. Those who have read the
paper may note that the Stansberry and Yelle [1999] borrows from and
extends the results of an earlier paper in Planetary and Space
Science:
Stansberry, J.A., D.J. Pisano, and R.V. Yelle
The emissivity of volatile ices on Triton and Pluto
Planet. Space Sci. 44, 945-955 (1996).
Abstract
http://www.elsevier.com/gej-ng/10/37/40/36...9/abstract.html
With that said, Stansberry and Yelle [1999] essentially argue that
even as Pluto recedes towards aphelion (i.e., as insolation per unit
area decreases) the equilibrium temperature of the nitrogen surface
ice-nitrogen vapor atmosphere (Teq), which they treat as a single
system, adjusts itself itself to Tab and remains constant. While
this system is treated singly, however, their model assumes the
presence of both phases of solid nitrogen (i.e., a single mixed-
phase) on Pluto's surface. Due to the emissivity contrast between
the two phases at Tab, the resulting latent heat fluxes (from
adsorption and release) tend to move the individual Teq for both
phases (either of which may be enriched locally) towards Tab. Since
Tab (35.6 K) is above the temperature at which the global
distribution of nitrogen ice is predicted to become non-isothermal
(31 K from Spencer et al., 1997 in "Pluto and Charon"), this keeps
the atmosphere from developing pressure (and temperature) gradients.
Stansberry and Yelle state that as long as T(N2)=Tab at aphelion
remains above 31 K, the predicted atmospheric pressure "will always
be larger than 1 ubar, and ... the atmosphere will remain in its
hydrostatic state."
It is an intriguing argument, though admittedly based on a couple of
assumptions: (1) the volatile tranport mechanisms on Pluto are
efficient enough in redistributing energy that imbalances (gradients)
do not arise; (2) though their paper is nominally directed towards
emissivities, as a practical matter (due to the difficulty in working
with and measuring the emissivity of a sufficiently large quantity of
nitrogen ice) their work has to rely on the simpler process of
measuring adorption coefficients combined with radiative transfer
theory.
That said, I believe this a slender reed for the DPS to hang a
cautionary recommendation of launching New Horizons by 2006. Indeed,
even Stansberry and Yelle note in their Icarus paper that other
published models (including one of their own) have different outcomes.
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?
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?
QUOTE (hendric @ Jul 27 2006, 09:44 AM)
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.
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.
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.
Why do you suggest it wouldn't scale to be a longer duration effect with a longer duration orbit?
Doug
Doug
QUOTE
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.
This doesn't make sense to me. If, for the sake of argument, the Earth were in a 44-day orbit, would the warmest day fall at the winter solstice 22 days later? Further, I think not much thermal inertia may be required to account for the Plutonian warming - with temperature differentials between seasons smaller and seasons longer than on Earth, a lesser thermal inertia could account for the effect. Also, nitrogen sublimation into the atmosphere is a cooling effect around perihelion... perhaps this cooling weakens as more polar nitrogen ices are consumed, helping to account for the warming?
The heat capacity of water - the oceans - is much greater than that of liquid nitrogen - also, the heat of evaporation of water is much higher than almost anything else. So as Richard has argued, it is difficult to see how the thermal inertia at pluto could create a significant lag between the heating and cooling cycle.
One other thought on the subject: In the dry artic air of Fairbanks Alaska, the mean temperature peaks earlier in July than in more temperate regions.
http://www.met.utah.edu/jhorel/html/wx/climate/maxtemp.html
One other thought on the subject: In the dry artic air of Fairbanks Alaska, the mean temperature peaks earlier in July than in more temperate regions.
http://www.met.utah.edu/jhorel/html/wx/climate/maxtemp.html
Perhaps Pluto current orbital position may be compared to the earth equivalent of 4:00 pm during the summer -- opposed to noon when the temp is lower though the sun is directly overhead. Here in Texas the temp usually peaks between 5-6 pm during the summer though the sun is lower in the sky -- hopefully New Horizons will be making its pass during Pluto’s orbital equivalent.
Yeah, I like to keep it simple...
Yeah, I like to keep it simple...
QUOTE (djellison @ Jul 27 2006, 08:11 PM)
Why do you suggest it wouldn't scale to be a longer duration effect with a longer duration orbit?
Doug
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)
QUOTE (ermar @ Jul 27 2006, 09:44 PM)
This doesn't make sense to me. If, for the sake of argument, the Earth were in a 44-day orbit, would the warmest day fall at the winter solstice 22 days later?
No. The thermal inertia would simply cancel any difference of temperature, as on Venus. The little remaining seasonal change would be shifted about 90° in phase (summer at autumn equinox). To have an inverted seasonal cycle would require another phenomenon, for instance that a temperature change tend to self-sustain and go beyond the cause. This is not the case with thermal inertia, which don't behave as a mechanical inertia.
A bit of maths: thermal inertia obeys a first order differencial equation, and has for electrical equivalent a resistor with a capacitor. It cannot produce phase shift more than 90°. Look a Doug's curve: the phase angle cannot be more than 90°
QUOTE (ermar @ Jul 27 2006, 09:44 PM)
Further, I think not much thermal inertia may be required to account for the Plutonian warming - with temperature differentials between seasons smaller and seasons longer than on Earth, a lesser thermal inertia could account for the effect. Also, nitrogen sublimation into the atmosphere is a cooling effect around perihelion... perhaps this cooling weakens as more polar nitrogen ices are consumed, helping to account for the warming?
Yes. What may happen is that, after hendric idea, if seasonal warming causes darkening of some zones, and thus more warming, this self-reinforcing effect could account for the 17 years lag on Pluto, as warming would still be increasing when the sun would be decreasing. But it is different of a thermal inertia, it is rather a positive feedback.
being irregular, it would also explain why the atmospheric pressure also varies irregularly.
QUOTE (Richard Trigaux @ Jul 28 2006, 07:57 AM)
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
Aouh! Doug, I did not realized one thing, that I understand from your post: the solstice on Pluto is not the moment where it receives the more/less heat. This would be true (in one hemisphere) if Pluto hat a perfectly circular orbit,as I was reasoning. But if it gets closer from the sun, say, 17 years after the summer solstice, it will receive the most heat at this moment, and be hotter at this moment. This has nothing to do with any kind of thermal inertia or self-increasing heating process with albedo variation. So you are correct with your 17 years lag. And there is no strange phenomenon allowing the thermal inertia to be 40 times that of Earth. Probably Pluto has a thermal inertia of at best some days, or anyway not detectable in a 249 years period.
Sorry, I know well the kind of calculations I was speaking, but you are better at knowing orbits of planets!
Sorry, I know well the kind of calculations I was speaking, but you are better at knowing orbits of planets!
QUOTE (The Messenger @ Jul 27 2006, 03:08 PM)
The heat capacity of water - the oceans - is much greater than that of liquid nitrogen
I'm not sure how that's relevant. There's certainly no liquid nitrogen on Pluto -- the pressure is far too low.
The question would be the thermal inertia of what there is on Pluto, and while we know the gross composition, for all we know there are slabs of solid CH4 covered with a thick layer of N2 frost. In the atmosphere-surface interaction, there may be phase change relationships. I think this is something you can model, but I don't see any definite answers in hand now. Of course, I could be convinced that some bounds could be placed on Pluto's thermal inertia, but do those bounds exclude the ~17 year lag?
Well Richard Trigaux tried to explain why there wouldnt be a 'long warm summer' on Pluto after solistice, or rather the closest pass to the sun which Pluto have gone past now going outward in orbit again.
And I think he did a good attempt at that.
Basic points are that Pluto dont have a thick atmosphere or one ocean that would be one resevoir for the little warming the planet have recieved. In short Pluto should not have any comparatively long 'summer' after the point it have passed closest to the sun but be more in equilibrium to the amount of sunlight it recieves in any point in its orbit.
This brings us back to the question at hand, and my thinking about this warming we see is that its caused by latent heat released when some component of Plutos atmosphere freeze out.
The remaining gasses gets one input of energy, so if this line of thinking are correct this warming is a comparatively transient phenomenon.
And I think he did a good attempt at that.
Basic points are that Pluto dont have a thick atmosphere or one ocean that would be one resevoir for the little warming the planet have recieved. In short Pluto should not have any comparatively long 'summer' after the point it have passed closest to the sun but be more in equilibrium to the amount of sunlight it recieves in any point in its orbit.
This brings us back to the question at hand, and my thinking about this warming we see is that its caused by latent heat released when some component of Plutos atmosphere freeze out.
The remaining gasses gets one input of energy, so if this line of thinking are correct this warming is a comparatively transient phenomenon.
QUOTE (Myran @ Jul 29 2006, 05:55 AM)
Basic points are that Pluto dont have a thick atmosphere or one ocean that would be one resevoir for the little warming the planet have recieved.
But it has mass. It's made of stuff. Stuff can contain thermal energy.
Doug
QUOTE (djellison @ Jul 29 2006, 12:15 AM)
But it has mass. It's made of stuff. Stuff can contain thermal energy.
Doug
Doug
Which only adds to the warming puzzle: If the atmosphere is temperary, ie, not gravitationally bound, it should add adiabatically to the cooling rate.
Why can it not be temporary AND gravitationally bound? Sublimiation and refreeze of various compounds etc.
Doug
Doug
QUOTE (Myran @ Jul 28 2006, 09:55 PM)
Well Richard Trigaux tried to explain why there wouldnt be a 'long warm summer' on Pluto after solistice, or rather the closest pass to the sun which Pluto have gone past now going outward in orbit again.
And I think he did a good attempt at that.
Basic points are that Pluto dont have a thick atmosphere or one ocean that would be one resevoir for the little warming the planet have recieved. In short Pluto should not have any comparatively long 'summer' after the point it have passed closest to the sun but be more in equilibrium to the amount of sunlight it recieves in any point in its orbit.
And I think he did a good attempt at that.
Basic points are that Pluto dont have a thick atmosphere or one ocean that would be one resevoir for the little warming the planet have recieved. In short Pluto should not have any comparatively long 'summer' after the point it have passed closest to the sun but be more in equilibrium to the amount of sunlight it recieves in any point in its orbit.
As a minor point, the issue is not if Pluto can store heat -- it's if it can store cold. If it's cooler at perihelion than one day before perihelion, that's because it's maintaining the cool temperatures of pre-perihelion.
For materials in a constant state, heating and cooling should be symmetric, and dependent only on thermal input and specific heat. If you like, compare Pluto's crust to some other planet (eg, Earth's) atmosphere, and it's not so insubstantial. But the devil's in the details.
QUOTE
JRehling wrote; As a minor point, the issue is not if Pluto can store heat -- it's if it can store cold.
Im certain that the ices and snows of Pluto can store some cold.
In reply to djellison
It would be hard to convince that the crust and snows on the surface of Pluto would be warmed up and so be kept warmed trough half the night like one sunwarmed rock can do on Earth.
What I intended to say was that Pluto would be far closer to "equilibrium to the amount of sunlight it recieves in any point in its orbit" than if it have had one substantial atmosphere or oceans. So I tried to keep my point to the simplest possible.
Now if we speculate that there are some subsurface reservoirs of nitrogen or any other gas, it could change the situation of course. If the little warming from the sun takes time to reach down to that level such could be a sink for heat.
Yet I did not mention the possibility for the simple reason that even if thats the case here, this effect might be so small its could be neglible. Because I know one basic fact, and that's the simple one that ices and snow are very bad conductors of heat.
So I fully agree, the devil's in the details.
I'm a bit confused by this topic and would love if someone would throw some light on things. So to speak.
The standard numbers I've seen for Pluto are that its surface temperature ranges from 40-50K. The Stefan Boltzman law says that the total energy (re)radiated per unit area is emissivity*SBConst*Temp^4.
Assume Pluto is a black body with a uniform temperature across the whole planet for a moment. Then the above gives us average radiation loss \ square metre that ranges from 0.145 to 0.354 watts/m^2.
Pluto ranges from 29.66AU to 49.31AU. The average amount of solar energy per square metre of surface area of a planet is given by - Solar Const at 1 Au /(Dist from Sun in AU)^2 / 4. The 4 comes from the ratio of the area of a circle to the surface area of a sphere and is needed to average the incident radiation across the whole planet.
Interestingly (or maybe not) those numbers come out fairly close to 0.14045 to 0.388194 watts/sq m (those correspond to temperatures of 39.67K and 51.15K respectively.
All of the above are kindo of so far so good bits of data but the real question about the lag between perihelion and maximum surface temperature clearly depends on the base radiation input\output balance but also must factor in instantaneous differences between that input\output energy ratio which some orbital modelling would help with, the thermal inertia of the surface, the effect of the planet's inclination\rotation (122deg, almost horizontal leading to _really_ long and extreme seasons) and finally any complications due to the atmosphere and the phase changes as it freezes out periodically.
The standard numbers I've seen for Pluto are that its surface temperature ranges from 40-50K. The Stefan Boltzman law says that the total energy (re)radiated per unit area is emissivity*SBConst*Temp^4.
Assume Pluto is a black body with a uniform temperature across the whole planet for a moment. Then the above gives us average radiation loss \ square metre that ranges from 0.145 to 0.354 watts/m^2.
Pluto ranges from 29.66AU to 49.31AU. The average amount of solar energy per square metre of surface area of a planet is given by - Solar Const at 1 Au /(Dist from Sun in AU)^2 / 4. The 4 comes from the ratio of the area of a circle to the surface area of a sphere and is needed to average the incident radiation across the whole planet.
Interestingly (or maybe not) those numbers come out fairly close to 0.14045 to 0.388194 watts/sq m (those correspond to temperatures of 39.67K and 51.15K respectively.
All of the above are kindo of so far so good bits of data but the real question about the lag between perihelion and maximum surface temperature clearly depends on the base radiation input\output balance but also must factor in instantaneous differences between that input\output energy ratio which some orbital modelling would help with, the thermal inertia of the surface, the effect of the planet's inclination\rotation (122deg, almost horizontal leading to _really_ long and extreme seasons) and finally any complications due to the atmosphere and the phase changes as it freezes out periodically.
Let me try to put all of this into layman's terms, for all of us who just don't think in terms of watts per square meter...
My understanding of thermal inertia is that this is a property of a body in which it attempts to achieve a thermal equilibrium, and that the time between a change in thermal input *or* output (i.e., changes in insolation or radiation) and reaching that equilibrium is the time in which inertia is holding the body back from achieving equilibrium.
Correct thus far?
All right, then -- from that basic understanding, it seems to me that the inertial rate of delay between a given change in radiation and/or insolation and the body reaching equilibrium is determined more by the rate at which the body either heats up or cools down than by the rate of change of insolation or radiation.
BTW, I know that a change in the rate of radiation is a basic change in how quickly the body heats up or cools down, and therefore affects that rate directly. My point, I guess, is that it seems like the characteristics of the body itself determine the thermal inertia of the body, NOT changes in its insolation.
That's why I can see Richard's point -- just stretching out the change in insolation from weeks to decades doesn't change the rate at which the body heats up or cools down. And, as such, it would seem that a body such as Pluto would have the same thermal inertia (all other forces being equal) if it orbited the Sun in a week or in two and a half centuries.
Of course, the temperatures of the surface and subsurface materials make a lot of difference to exactly how quickly Pluto heats up and cools down, and those materials change state depending on the overall heat budget. Which changes the heating/cooling rate, and thus the body's thermal inertia. If you put Pluto in a tight orbit about the Sun, its thermal inertia would change drastically, because its surface and subsurface materials would change state pretty drastically. But if you could change Pluto's insolation cycle -- not the intensity of insolation, just the rate of change it encounters between aphelion and perihelion -- from decades to weeks, I think that what Richard and others are saying is that since the surface materials would not change drastically, it ought to exhibit the same thermal inertia as it displays now. And that the move to equilibrium should take the same amount of time, regardless of the length of time it takes for the insolation to change from maximum to minimum.
So, please, tell me what I'm getting wrong, here, if indeed a body's thermal inertia is dependent on the rate of change of insolation, as many of you seem to be suggesting...
-the other Doug
p.s. -- it occurs to me that we've only ever seen Pluto while it has an atmosphere. What proof do we have that the atmosphere really *does* freeze out? Are we certain of this, or is it just a theory based on insolation levels and best-guesses as to Pluto's surface composition? Thanks! DVD
My understanding of thermal inertia is that this is a property of a body in which it attempts to achieve a thermal equilibrium, and that the time between a change in thermal input *or* output (i.e., changes in insolation or radiation) and reaching that equilibrium is the time in which inertia is holding the body back from achieving equilibrium.
Correct thus far?
All right, then -- from that basic understanding, it seems to me that the inertial rate of delay between a given change in radiation and/or insolation and the body reaching equilibrium is determined more by the rate at which the body either heats up or cools down than by the rate of change of insolation or radiation.
BTW, I know that a change in the rate of radiation is a basic change in how quickly the body heats up or cools down, and therefore affects that rate directly. My point, I guess, is that it seems like the characteristics of the body itself determine the thermal inertia of the body, NOT changes in its insolation.
That's why I can see Richard's point -- just stretching out the change in insolation from weeks to decades doesn't change the rate at which the body heats up or cools down. And, as such, it would seem that a body such as Pluto would have the same thermal inertia (all other forces being equal) if it orbited the Sun in a week or in two and a half centuries.
Of course, the temperatures of the surface and subsurface materials make a lot of difference to exactly how quickly Pluto heats up and cools down, and those materials change state depending on the overall heat budget. Which changes the heating/cooling rate, and thus the body's thermal inertia. If you put Pluto in a tight orbit about the Sun, its thermal inertia would change drastically, because its surface and subsurface materials would change state pretty drastically. But if you could change Pluto's insolation cycle -- not the intensity of insolation, just the rate of change it encounters between aphelion and perihelion -- from decades to weeks, I think that what Richard and others are saying is that since the surface materials would not change drastically, it ought to exhibit the same thermal inertia as it displays now. And that the move to equilibrium should take the same amount of time, regardless of the length of time it takes for the insolation to change from maximum to minimum.
So, please, tell me what I'm getting wrong, here, if indeed a body's thermal inertia is dependent on the rate of change of insolation, as many of you seem to be suggesting...
-the other Doug
p.s. -- it occurs to me that we've only ever seen Pluto while it has an atmosphere. What proof do we have that the atmosphere really *does* freeze out? Are we certain of this, or is it just a theory based on insolation levels and best-guesses as to Pluto's surface composition? Thanks! DVD
I can see two possible causes for the delayed maximum temperature of Pluto.
One cause is a couple of positive feedbacks amplifying the temeperature change. First, as the bright ice sublimates they uncover darker surface and leave behind the dark materials produced by cosmic radiation. This lowers the albedo causing it to absorb more sunlight. Second the atmosphere creates a greenhouse effect. This traps the extra energy absorbed further amplifying the the warming.
There is also the phase change involved. A phase change should absorb much more energy than would be required just to increase the temperature of an already existing atmosphere or the surface itself. This may delay the formation of a significant atmosphere until after it is closer to perihelion than is necessary to maintain it.
Wanndering a bit off thread, I think there may some similar positve feedbacks may be involved in how the earth responds to the Milankovich cycles to produce the Ice Ages. First the increased insolation in the northern hemishpere causes ice caps to melt increasing the albedo of the earth leading to warmer temperatures. Second the carbon dioxide and methane trapped in the permafrost are release as it melts further amplifying the temperature increase. (Ironically this could mean the higher temperatures caused the increase in greenhouse gases that track closely to the temperature. Don't tell Al Gore, his head might explode ) These positive feedbacks may explain why the temperatures increases so fast as the ice age ends. Who know we may learn something about global warming on Earth by studying it on Pluto.
One cause is a couple of positive feedbacks amplifying the temeperature change. First, as the bright ice sublimates they uncover darker surface and leave behind the dark materials produced by cosmic radiation. This lowers the albedo causing it to absorb more sunlight. Second the atmosphere creates a greenhouse effect. This traps the extra energy absorbed further amplifying the the warming.
There is also the phase change involved. A phase change should absorb much more energy than would be required just to increase the temperature of an already existing atmosphere or the surface itself. This may delay the formation of a significant atmosphere until after it is closer to perihelion than is necessary to maintain it.
Wanndering a bit off thread, I think there may some similar positve feedbacks may be involved in how the earth responds to the Milankovich cycles to produce the Ice Ages. First the increased insolation in the northern hemishpere causes ice caps to melt increasing the albedo of the earth leading to warmer temperatures. Second the carbon dioxide and methane trapped in the permafrost are release as it melts further amplifying the temperature increase. (Ironically this could mean the higher temperatures caused the increase in greenhouse gases that track closely to the temperature. Don't tell Al Gore, his head might explode
) These positive feedbacks may explain why the temperatures increases so fast as the ice age ends. Who know we may learn something about global warming on Earth by studying it on Pluto.
QUOTE (JRehling @ Jul 28 2006, 03:27 PM)
I'm not sure how that's relevant. There's certainly no liquid nitrogen on Pluto -- the pressure is far too low.
The question would be the thermal inertia of what there is on Pluto, and while we know the gross composition, for all we know there are slabs of solid CH4 covered with a thick layer of N2 frost. In the atmosphere-surface interaction, there may be phase change relationships. I think this is something you can model, but I don't see any definite answers in hand now. Of course, I could be convinced that some bounds could be placed on Pluto's thermal inertia, but do those bounds exclude the ~17 year lag?
The question would be the thermal inertia of what there is on Pluto, and while we know the gross composition, for all we know there are slabs of solid CH4 covered with a thick layer of N2 frost. In the atmosphere-surface interaction, there may be phase change relationships. I think this is something you can model, but I don't see any definite answers in hand now. Of course, I could be convinced that some bounds could be placed on Pluto's thermal inertia, but do those bounds exclude the ~17 year lag?
Suppose there was nitrogen under the surface of parts of Pluto, with that subsurface nitrogen melting into liquid (except for a surface covering of ices) during the Plutonian summer and freezing out again during the Plutonian winter.
If there was sufficient nitrogen to form (subsurface) pools or lakes (or even oceans) if and when it did melt could this be used to explain the apparent rise in temperate, whether through thermal inertia, venting to the surface now and again, or some other mechanism?
======
Stephen
Pluto's latent heat is a part of the generalized thermal inertia. I think many of you will enjoy
reading, "Why is Pluto Bright?" Icarus, 75, 485-498 (1988). Much of what is being discussed
this weekend is touched on in that almost 20-year old paper. Trafton's 7-17 year phase lag in
albedo reversal, the evidence for atmospheric formation, etc. are all discussed.
reading, "Why is Pluto Bright?" Icarus, 75, 485-498 (1988). Much of what is being discussed
this weekend is touched on in that almost 20-year old paper. Trafton's 7-17 year phase lag in
albedo reversal, the evidence for atmospheric formation, etc. are all discussed.
The full article doesn't seem to be available on Science Direct, possibly because the issue is too old:
http://www.sciencedirect.com/science?_ob=A...a0fa317a229d6eb
I hope you don't mind Alan if I quote the abstract:
So an inactive object that started covered in high albedo CH4 would gradually lose its brightness due to radiation and micrometeorites? I guess that implies that Pluto's dark areas are the old terrain, with the bright areas locations scoured clean by large impacts and/or volcanic activity. Are we starting pools yet on what Pluto will look like?
...And that Charon's dark low-volatile surface covers extends to its depths, since impacts would expose volatile ices, if there were any.
For 2003 UB313, it is so uniformly bright that the current hypothesis is that the atmosphere has frozen out over the entire surface. That just doesn't sound likely to me, given that albedo differences would tend to be amplified over time. Since they would be the warmest areas, darker areas would be covered slowest. This would give them more exposure to radiation etc, and would tend to keep their cover thinner than lighter areas, creating a positive feedback loop. So to get a "white" planet requires some sort of active process that continues overlaying material on darker areas when it is too cold for their albedo to matter, similar to Enceladus. My bet is that we'll eventually find some traces of outgassing.
http://www.sciencedirect.com/science?_ob=A...a0fa317a229d6eb
I hope you don't mind Alan if I quote the abstract:
CODE
Why is Pluto bright? Implications of the albedo and lightcurve behavior of Pluto
S. Alan SternaLaurence M. TraftonbG. Randall Gladstonec
a Department of Astrophysical, Planetary, and Atmospheric Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80309-0392, USA
b Department of Astronomy and McDonald Observatory, University of Texas 78712, USA
c Space Sciences Laboratory, University of California at Berkeley, Berkeley, California 94720, USA
Received 6 October 1987; revised 31 December 1987. Available online 14 October 2002.
Abstract
Methane is abundant on Pluto, however, CH4 rapidly darkens in the Plutonian solar insolation and charged particle environment. We therefore call attention to the fact that Pluto's high albedo is at odds with the observation of methane frost on Pluto's surface. We examine a variety of mechanisms to resolve this dilemma, and conclude that Pluto's surface is being replenished with fresh (bright) volatile frosts. We propose that this replenishment is due to orbitally driven sublimation and freezout of volatiles in the atmosphere. Thus, Pluto's high albedo adds to the case for an atmosphere, and argues for annual volatile transport cycles. Orbitally driven replenishment can also account for the observed secular changes in Pluto's lightcurve. We show that thermally driven sublimation is capable of replacing volatiles lost to escape and photolysis. Our model is consistent with present data on the surface composition, albedo, aldebo distribution, and surface color of Pluto, and presents an explanation of the time variability of Pluto's lightcurve. Charon's darker albedo is consistent with our model because Charon's surface is today devoid of volatiles. We predict that the secular variation in Pluto's rotational lightcurve should reverse 7–17 years after perihelion due to the thermal inertia of Pluto's surface. Based on the minimum mass of CH4 required to cover newly created dark hydrocarbons each Pluto year, we develop a lower limit of 7–70 cm-am on Pluto's maximum atmospheric abundance. Based on the time-lag constraint, we develop a lower limit of between 16 and 45 cm-am on Pluto's present atmospheric abundance. Finally, we discuss a number of observational tests for our model.
S. Alan SternaLaurence M. TraftonbG. Randall Gladstonec
a Department of Astrophysical, Planetary, and Atmospheric Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80309-0392, USA
b Department of Astronomy and McDonald Observatory, University of Texas 78712, USA
c Space Sciences Laboratory, University of California at Berkeley, Berkeley, California 94720, USA
Received 6 October 1987; revised 31 December 1987. Available online 14 October 2002.
Abstract
Methane is abundant on Pluto, however, CH4 rapidly darkens in the Plutonian solar insolation and charged particle environment. We therefore call attention to the fact that Pluto's high albedo is at odds with the observation of methane frost on Pluto's surface. We examine a variety of mechanisms to resolve this dilemma, and conclude that Pluto's surface is being replenished with fresh (bright) volatile frosts. We propose that this replenishment is due to orbitally driven sublimation and freezout of volatiles in the atmosphere. Thus, Pluto's high albedo adds to the case for an atmosphere, and argues for annual volatile transport cycles. Orbitally driven replenishment can also account for the observed secular changes in Pluto's lightcurve. We show that thermally driven sublimation is capable of replacing volatiles lost to escape and photolysis. Our model is consistent with present data on the surface composition, albedo, aldebo distribution, and surface color of Pluto, and presents an explanation of the time variability of Pluto's lightcurve. Charon's darker albedo is consistent with our model because Charon's surface is today devoid of volatiles. We predict that the secular variation in Pluto's rotational lightcurve should reverse 7–17 years after perihelion due to the thermal inertia of Pluto's surface. Based on the minimum mass of CH4 required to cover newly created dark hydrocarbons each Pluto year, we develop a lower limit of 7–70 cm-am on Pluto's maximum atmospheric abundance. Based on the time-lag constraint, we develop a lower limit of between 16 and 45 cm-am on Pluto's present atmospheric abundance. Finally, we discuss a number of observational tests for our model.
So an inactive object that started covered in high albedo CH4 would gradually lose its brightness due to radiation and micrometeorites? I guess that implies that Pluto's dark areas are the old terrain, with the bright areas locations scoured clean by large impacts and/or volcanic activity. Are we starting pools yet on what Pluto will look like?
...And that Charon's dark low-volatile surface covers extends to its depths, since impacts would expose volatile ices, if there were any.
For 2003 UB313, it is so uniformly bright that the current hypothesis is that the atmosphere has frozen out over the entire surface. That just doesn't sound likely to me, given that albedo differences would tend to be amplified over time. Since they would be the warmest areas, darker areas would be covered slowest. This would give them more exposure to radiation etc, and would tend to keep their cover thinner than lighter areas, creating a positive feedback loop. So to get a "white" planet requires some sort of active process that continues overlaying material on darker areas when it is too cold for their albedo to matter, similar to Enceladus. My bet is that we'll eventually find some traces of outgassing.
Horrible thought... suppose that Pluto is setting up for a "planet-wide smog storm" like Mariner 9's "planet wide dust storm" in 1971?
I'm not serious, but the thought did cross my mind...
--Bill
I'm not serious, but the thought did cross my mind...
--Bill
Does Pluto’s atmosphere go through the fast-freeze?
A study of Pluto’s bright frosts suggests that the way the planet cools down is rapid and disorganised. The results were presented at the European Planetary Science Congress in Berlin.
http://www.europlanet-eu.org/index.php?opt...7&Itemid=32
A study of Pluto’s bright frosts suggests that the way the planet cools down is rapid and disorganised. The results were presented at the European Planetary Science Congress in Berlin.
http://www.europlanet-eu.org/index.php?opt...7&Itemid=32
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