NASA spacecraft may have finally found the mysterious source of gullies on Mars: melting snow.

http://science.nasa.gov/headlines/y2003/19feb_snow.htm?list760961

I thought CO2 was a more likely culprit as of late, given the temperatures were well below 0 centigrade...

must have been hotter then....

I do believe some of the evidence is recent and currently going on.

Else the dust storms would take care of a lot of the signs.

Trying to see if i can post a Mars picturehttp://us.news2.yimg.com/us.yimg.com/p/net/20030220/capt.6155646.jpg



Research suggests that the mysterious gullies on Mars were made by water trickling from the melting of snow that had built up over thousands of years. This July 14, 1999, photo shows gully features apparently carved by seepage and runoff of liquid water on Mars in the geologically recent past. The image was taken by the Mars Orbiter Camera (MOC) aboard NASA's Mars Global Surveyor (MGS). (AP Photo/NASA/JPL/ Malin Space Science Systems)

http://antwrp.gsfc.nasa.gov/apod/image/0302/snowmars_odyssey.jpg

Melting Snow and the Gullies of Mars
Credit: P. Christensen (ASU), THEMIS, Mars Odyssey, NASA

Tantalizing images of gullies on Mars have offered striking evidence for recent flows of liquid water. But Mars is too cold and its atmosphere too thin for liquid water to exist on the surface. Still a new and compelling explanation for gullies carved by liquid water was inspired by this recently released image from the Mars Odyssey spacecraft. Pictured is a section of what is likely a snow covered crater in the Martian southern hemisphere. North is at the top and the scene, illuminated from the left, is about 16 kilometers wide. Patches of smooth snow pack remain along the northern crater wall, while structures resembling the famous Martian gullies appear to be emerging as the snow cover gradually disappears, and are exposed along the crater's western (left) wall. Melting snow, running underneath the snow pack and down the crater walls would be protected from the extreme surface conditions, remaining liquid and eroding the gullies over time. Could life exist in a liquid water environment beneath the Martian snow

Going further...

So was this really snow or just ice? Snow would imply an atmosphere, correct? Or does Mars already have an atmopshere? I dont remember.

A very thin atmosphere, about 1/100th of Earth's I think.

Wet1, I see how maybe pressure and isolation would keep water from instantly freezing, but the next question would be, what's making it melt? Weren't some of the temperates in these areas around -130 degrees C? Seems too cold even for below surface thawing...CO2 on the other hand...

Someone go and see first hand...put this to rest. :)

A very thin atmosphere, about 1/100th of Earth's I think.

Is it made of hydrogen? or O3? Or many different gasses?

What is the gas found on the surface? I havent done alot of Mars research, sorry.

A mixture, primarily CO2...very little Oxygen, so that's one of the things terraformers would have to either get from the water, or import.

Not sure on the exact ratios, or the other gases, like Nitrogen.

It's enough to blow things around during the dust storms, but to do so requires high speeds, being so thin. A storm of 50 mph winds would feel like a gentle Earth breeze to an astronaut standing on the surface.

Mars' atmosphere is mostly CO2, with traces of some other stuff. Strangely enough, it's almost exactly the same composition as Venus' atmosphere, just much much more diffuse.

Check out this Fact Sheet (http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html) To learn more about Mars.

What is making it melt is the low atmospheric pressure that Mars has. Add to that, during the right time of the year the temperature climbs enough to allow melting, depending on the latitude.

Wet1 ...

How does pressure relate to temperature? Based on the previous link to a "fact sheet" it would appear that the average temperature on Mars is always negative (Celsius) which - based on Earth science - would indicate that snow should not be melting there at any time.

I patiently await a science lesson!

E

Lowering the atmospheric pressure will reduce the melting and boiling points accordingly, as raising the pressure will raise them. That's why pressure cookers work or why you have special cooking instructions for high altitudes.

I don't know how low water's melting point would go in 1/100 atms....

Why do they think that it is melting ice and not caused by sand dune 'slippage'?

Is it the ravines which are the evidence?

That's an open-minded point. If inner-planetary warming was a concern that should have been the next point made. Question is -how active is the planet?

What Jaxom mentioned about pressure/temperature relationship is very true.

Freezing and boiling points are greatly affected by pressure. A matter of pounds is of intense interest to manufacturers and chemical makers.

Temperature is another of great interest. As can readily imagined temperature controls a lot of things that happen. One of the uses that come to mind immeadately is that of the tight seal on foods and products. Most of the time time product is put into the container hot. As it cools it helps to lock in place that lid.

Temperature and pressure are intimately related and of great use, to the consumer of products, the manufacturer of those products, and to the determination of physical properties.