Billions of years ago the atmosphere on Mars was warm enough for flowing rivers, lakes and oceans

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“Using an imaging spectrometer on MRO, researchers detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet. These darkish streaks appear to ebb and flow over time. They darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times,” NASA announced in a press release.

“It took multiple spacecraft over several years to solve this mystery, and now we know there is liquid water on the surface of this cold, desert planet,” Mr. Meyer said in a press release. “It seems that the more we study Mars, the more we learn how life could be supported and where there are resources to support life in the future.”

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“The origin of water forming the Recurring Slope Linae is not understood, given the extreme aridity of Mars’ surface environment. Water could form by the surface/sub-surface melting of ice, but the presence of near-surface equatorial ice is highly unlikely. Water could also form via deliquescence by hygroscopic salts, although it is unclear how the Martian atmosphere can sufficiently supply water vapor every year to create RSL. The absence of concentrated deliquescent salts would rule out this hypothesis. Another hypothesis is seasonal discharge of a local aquifer, which concentrates salt deposits as the brine evaporates, but then lineae emulating from the tops of local peaks are difficult to explain. It is conceivable that RSL are forming in different parts of Mars via different formation mechanisms. The new compositional insights reported here from widely separated sites provide essential new clues.”

http://observer.com/2015/11/new-data...rs-water-went/