Evidence From Rocks and Minerals
Today, it is accepted that Mars had abundant water very early in its history. Today, all large areas of liquid water have disappeared. A fraction of this water is however retained on modern Mars as both ice and locked into the structure of abundant water-rich materials, including clays and sulfates.
Despite this, olivine is widespread on Mars, which readily weathers to iddingsite in the presence of water. Iddingsite is observed on Mars, confirming that water has been present at times, and this might enable scientists to determine when there was last liquid water on the planet. However the abundance of olivine alongside it demonstrates that Mars' surface has not been pervasively altered by water. Studies of hydrogen isotopic ratios indicate that asteroids and comets from beyond 2.5 AU provide the source of Mars' water, which currently totals 6% to 27% of the Earth's present ocean.
Since several missions (Mars Odyssey, Mars Global Surveyor, Mars Reconnaissance Orbiter, Mars Express, Opportunity rover and Curiosity rover) are still sending back data from Mars, discoveries continue to be made.
Read more about this topic: Water On Mars
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