YosemiteSam
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Here's ice in a crater in the northern plains on Mars - the region with the wonderful name Vastitas Borealis.
Many scientists believe this huge plain was an ocean during the Hesperian Epoch, a period of Martian history that stretches from about 3.5 to about 1.8 billion years ago. Later, around the end of the Hesperian, they think about 30% of the water on Mars evaporated and left the atmosphere, drifting off into outer space... part of the danger of life on a planet without much gravity. The oceans then froze. Most of them very slowly sublimated, disappearing into water vapor without ever melting. This water vapor was lost to outer space.
But there's still a lot of water left. The north pole has an ice cap with 820,000 cubic kilometers of ice! That's equal to 30% of the Earth's Greenland ice sheet - enough to cover the whole surface of Mars to a depth of 5.6 meters if it melted, if we pretend Mars is flat. And the south pole is covered by a slab of ice about 3 kilometers thick, a mixture of 85% carbon dioxide ice and 15% water ice, surrounded by steep slopes made almost entirely of water ice. This has enough water that if it melted it would cover the whole surface to a depth of 11 meters!
There's also lots of permafrost underground, and frost on the surface, and bits of ice like this. This picture was taken by the Mars Express satellite:
• Water ice in crater at Martian north pole, ESA, http://www.esa.int/esaMI/Mars_Express/SEMGKA808BE_3.html
https://lh5.***BROKEN***/-MKQ2ftyVmXQ/UHbcZ5TF5dI/AAAAAAAAQig/0HPwmZas9j4/s750/mars_crater_ice.jpg
Many scientists believe this huge plain was an ocean during the Hesperian Epoch, a period of Martian history that stretches from about 3.5 to about 1.8 billion years ago. Later, around the end of the Hesperian, they think about 30% of the water on Mars evaporated and left the atmosphere, drifting off into outer space... part of the danger of life on a planet without much gravity. The oceans then froze. Most of them very slowly sublimated, disappearing into water vapor without ever melting. This water vapor was lost to outer space.
But there's still a lot of water left. The north pole has an ice cap with 820,000 cubic kilometers of ice! That's equal to 30% of the Earth's Greenland ice sheet - enough to cover the whole surface of Mars to a depth of 5.6 meters if it melted, if we pretend Mars is flat. And the south pole is covered by a slab of ice about 3 kilometers thick, a mixture of 85% carbon dioxide ice and 15% water ice, surrounded by steep slopes made almost entirely of water ice. This has enough water that if it melted it would cover the whole surface to a depth of 11 meters!
There's also lots of permafrost underground, and frost on the surface, and bits of ice like this. This picture was taken by the Mars Express satellite:
• Water ice in crater at Martian north pole, ESA, http://www.esa.int/esaMI/Mars_Express/SEMGKA808BE_3.html
https://lh5.***BROKEN***/-MKQ2ftyVmXQ/UHbcZ5TF5dI/AAAAAAAAQig/0HPwmZas9j4/s750/mars_crater_ice.jpg
