Discovery Story: Salty Water Flows on Mars Today, Boosting Odds for Life
The announcement that liquid, salty water has been found flowing on the surface of Mars came as no real surprise to astronomers. Mars is full of water, mostly in the form of ice at the poles and under the surface. Also, Martian air is surprisingly humid: up to 100 percent humidity on cold winter nights.
The clearest evidence for liquid water on Mars comes from dark streaks known as recurring slope linnea (RSL). These streaks form in the spring and disappear later in the Martian year.
Spectroscopic analysis showed that the streaks are hydrated perchlorate, a briny liquid of perchlorate salt with water trapped in its crystals.
The salt causes water to remain liquid at much lower temperatures than on Earth. Perchlorate brine can stay liquid down to minus 94 degrees Fahrenheit (minus 70 degrees Celsius). The brine boils at 75 degrees F (24 degrees C), close to the highest summertime temperature on the surface of Mars.
Scientists estimate that 4.3 billion years ago, Mars had a huge ocean covering its entire northern hemisphere. This ocean would have contained more water than Earth’s Arctic Ocean.
Indications are that some of Mars' water is still there, frozen beneath the surface. A giant slab of ice as big as California and Texas combined, and as deep as a 13-story building, lies beneath the surface of Mars between the planet's equator and north pole, researchers say.
The Mars rover Curiosity weather station shows that the thin Martian air is surprisingly humid. Curiosity's measurements range from about 5 percent humidity on summer afternoons to up to 100 percent (saturation point) on autumn and winter nights.