Comments on: Frozen pond on Pluto

By: Edward

Edward — Thu, 31 Mar 2016 20:58:19 +0000

Rocco,
In recent decades, scientists have discovered that ice has different characteristics at different temperatures and pressures. You may want to consider looking into the “phases” of ice as a nice distraction from the problems of the day.
https://en.wikipedia.org/wiki/Ice#Phases

I remember the reasoning for the urgency of sending a probe to Pluto, back when they were proposing it.

By: Rocco

Rocco — Thu, 31 Mar 2016 11:18:28 +0000

@Edward
A nice comment on sublimation which btw gives me a push to dig further into the area of sublimation.
And an added thanks for the information about the New Horizons mission to look at the atmosphere of Pluto. Interesting stuff.

By: Edward

Edward — Mon, 28 Mar 2016 00:56:11 +0000

Rocco,
Water sublimation stops below a certain temperature. The vapor pressure drops too low for there to be measurable sublimation. This happens with many substances, such as iron, which does not sublimate at room temperature. If my (faulty) memory (mis)serves me, the temperature at which water stops sublimating is around -150 centigrade.

Because vapor pressure for substances disappears at cold temperatures, the atmosphere for Pluto disappears when it gets too far from the sun, and the New Horizons scientists wanted to send the probe to Pluto before the atmosphere condensed back onto the surface. There was urgency during the proposal, assembly, and launch phases of the project, and it was this urgency that is why Pluto was put ahead of other proposals. Missing the atmosphere this decade would have required another couple of centuries of waiting for the next opportunity to get a look at it. It is also why they chose to use their weight budget for additional instruments rather than a heavier but faster transmitter.

Looking at the atmosphere backlit by the sun is why they chose closest approach on the dark side of Pluto. This allowed them to see the chemical makeup of the atmosphere but hindered their look at the surface.

By: Rocco

Rocco — Sun, 27 Mar 2016 18:57:52 +0000

@Local Fluff
Yes I get the water below the surface may still be around, but against the vacuum it would sublimate off planet. I guess my question is, does Nitrogen sublimate like water when exposed to a vacuum if not already in a solid form?

By: Local Fluff

Local Fluff — Sun, 27 Mar 2016 15:25:09 +0000

@Rocco
Pluto’s air pressure is 1/100,000 of that on Earth. It is vacuum. The atmosphere is only interesting for tiny material transports over geological times. Nitrogen freezes at about 60 Kelvin regardless of pressure. But it doesn’t get very hard, water ice is believed to build up the mountains on Pluto, only covered by nitrogen.

By: Rocco

Rocco — Sun, 27 Mar 2016 12:33:11 +0000

Do we know the surface pressure to keep the Nitrogen in a frozen state? I am wondering about the psi since we know the cold is there and we need both to make a solid form. At least here on Earth anyway.

By: Dick Eagleson

Dick Eagleson — Sat, 26 Mar 2016 23:43:10 +0000

All right! We have a venue for all the skating events of the 2218 Winter Games!