Pluto is Much Colder Than Expected

IZ Reloaded writes "Any would be travellers to Pluto should bring extra winter gear. The new temperature on Pluto according to scientists is 43 degrees Kelvin. That's 10 degrees Kelvin colder than expected. From CNN: "Astronomers think Pluto's colder than expected temperature reading involves interactions between nitrogen ice on the planet's surface and the nitrogen gas that makes up its atmosphere...Pluto is a dynamic example of what we might call an anti-greenhouse effect...""

Comments

Not degrees

[whmac33]

Could I be the first to point out that it's just 10 Kelvin? no degrees here

For the lazy

[krunoce]

43 kelvin

= -382.27 degrees Fahrenheit
= -230.15 degrees Celsius

= really fucking cold outside.

Sensational + by someone without a science degree

[Dzimas]

The correct use is "43 kelvins." Unlike degrees Celsius or degrees Fahrenheit (both adjectives), it is a noun, and the correct pluralization is kelvins.

I'm sure some newspaper will soon start running headlines about how Pluto is "23% colder than anticipated." In the real world, 10 K isn't that much, although it would be nice to know why our estimates are off. For reference, water freezes at 273.15 K, and the deepest darkest nook of outer space registers about 2.7 K, thanks to some background microwave radiation.

Re:hmm

[Vellmont]

I don't understand why it would require so much more insulation. Isn't heat transfer proportional to the difference in temperature of each side? So if you wanted to maintain your equipment at 0c, that's 273K-43K = 230 vs 273K-53K= 220. The heat transfer of the material is a constant, so 230/220 = 1.045, so about 4.5% thicker insulation.

Re:In other words

[techno-vampire]

Maybe the dark side of Mercury would be more feasible.

What "dark side of Mercury?" It's been known for over twenty years that Mercury rotates in 2/3 of the time it takes to orbit the sun rather than having its day equal to its year. It's just that the best times to observe the planet by telescope come about 2/3 or 4/3 of an orbit apart. (Not sure which one, but in either case, the same side was always lit when we could observe it. It took doppler radar to find out what was really going on.)

Re:About this anti-greenhouse effect...

[craXORjack]

No. Pluto only has an atmosphere during its summer which it is currently in. (It is closer to the sun at 30AU than it will be again for a very long time) During the winter the atmosphere will give up it's heat and fall to the surface as solid nitrogen snow where it will sit for a couple hundred years until the sun once again turns it from solid to gas. But the surface will always stay at the same temperature. This is the same effect seen when you measure the temperature of water with ice cubes in it. The water will stay at 32 degrees until all the ice is gone even if you put a flame underneath. The added heat would merely make the ice melt faster rather than raise the water temperature.

Re:hmm

[gauge boson]

Actually, the electronics needs to work also during the trip, where the temperature is about 2.7 K.

Not really. The temperature of the heliosphere is actually rather high -- don't remember exactly offhand, but it's higher than the interstellar medium, which is somewhere around 7000K (give or take a couple thousand Kelvins). It's just that it stores almost no heat, since there's so little matter. (This is slightly sloppy wording, but close enough.) The upshot is that there is almost no heat conduction in either direction and almost all heat transfer occurs by blackbody radiation, which is amazingly inefficient. Even though Pluto doesn't have an atmosphere, touching the surface changes this entirely by providing a material to transfer heat to -- that's why a probe landing on Pluto would need a lot of insulation that a non-landing probe (e.g., V'ger) wouldn't.

Re:hmm

[gauge boson]

That's not the temperature of the interstellar medium, it's the temperature of the cosmic background radiation -- they are completely different. I can see where the confusion could come from, though. Short version:

• Cosmic Microwave Background: The residual heat of the big bang, redshifted (cooled) by ~13 billion years of expansion. This temperature is given in terms of the Stefan-Boltzmann relation (blackbody temperature), and basically represents the average temperature of the whole universe, including the vast, cold, empty intergalactic regions.
• Interstellar Medium: A very diffuse (though still dense compared to the intergalactic regions) cloud of ionized gas filling the whole galaxy. These ionized particles move around very quickly, i.e., they're very hot (Maxwell-Boltzmann distribution). 7000K +/- 2000K according to this synopsis, at least for regions near the heliosphere.
• Heliosphere: The gaseous bubble surrounding the sun out to about 100AU (Voyager 1 hit the termination shock where it meets the ISM at 94AU). It's hotter and denser than the interstellar medium, and it's where any space probe we launch would be travelling. Of course, since there is so little gas in even the heliosphere (its pressure would be considered a hard vacuum on Earth), these temperatures have very little effect on any spacecraft.