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Originally posted by NGC2736
On topic, do we now have proof of NASA playing fast and loose with data? Or is this another example of NASA being too smart to use common sense? Or are we missing something here?
Originally posted by ArMaP
The last data available, from Sol 22, is:
Min. temperature: -80ºC
Max. temperature: -32ºC
Pressure: 8.29 milibar
How can water ice go straight from being a solid to being a gas (sublimation)?
Just like dry ice does here on Earth, water ice goes from solid to gas when the pressure is below 6.1 millibars and it gets heated (like it does in the Martian sun). It can also go straight from solid to gas above 6.1 millibars when the vapor pressure (amount of water vapor in the air) is low enough. This is because the molecules of water in solid form and gas form are not at equilibrium.
You might be surprised to know that the same thing happens here on Earth. If you have a frost-free freezer, you may have noticed that your ice cubes gradually shrink over a period of days. This is sublimation: the fan is constantly sucking water vapor out of the freezer so the ice cubes surrender more and more water molecules to the dry air over time.
The pressure on Mars is about 8 millibars, very close to the "triple point" of water, which is the point where it can easily exist as either a solid, a liquid or a gas (see the chart below). Since the vapor pressure is so low, water can easily sublime in the Martian atmosphere, especially as the surface heats up in the sunshine. When that happens, the soil can often get hotter than the air in the sunshine (think of a lizard sunbathing on a hot rock).
Holy cow. That's what the scientists said when they saw this picture of the ground underneath the lander. The two flat, bright surfaces look like ice, which was the reason Phoenix was sent to the arctic region. These patches, which have been named "Holy Cow," are out of reach of the robotic arm. However, ice should be close to the surface all around the lander and within easy reach.
Photo: NASA Jet Propulsion Laboratory and University of Arizona