Monday, September 29, 2008

It Snows on Mars

Mars Lander Sees Falling Snow, Soil Data Suggest Liquid Past "A laser instrument designed to gather knowledge of how the atmosphere and surface interact on Mars, detected snow from clouds about 2.5 miles above the spacecraft's landing site. Data show the snow vaporizing before reaching the ground."


Richard said...

Rain that doesn't reach the ground is called Virga. Is there a similar word for snow that doesn't reach the ground (at all, not as rain, sleet or freezing rain)? Does that even happen on Earth? The article didn;t say exactly what the "snow" was. Was it water ice or something else?

Howard said...

Even the NASA release doesn't say. I assume they don't know or it's water.

On Earth, if snow fell but vaporized before hitting the ground, wouldn't it go through a liquid stage and therefore be called rain? Isn't rain or snow differentiated by what form it's in when it hits the ground, since it all starts as ice crystals in clouds? Hence the need for a word like virga, but calling it rain that doesn't hit the ground isn't quite right.

Richard said...

If it was colder than the freezing point of water and very dry then I could imagine a situation where the snow sublimed before it hit the ground but did not melt first. I am not sure that it would do that fast enough or that if those conditions existed that you would have snow in the first place. I am also to lazy to pull out a chemical engineering book and try to figure it out.

We will need words for these phenomena when we visit other planets and the things that fall out of the sky are not water but some other compounds like carbon dioxide which sublimes, or methane, or nitrogen if it is really cold. Maybe lead if it is really hot.