Liquid water on Mars can and DOES exist - but only for a few hours every day in the spring and summer, claim scientists
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Most of our studies of Mars so far have focused on whether water could have once existed on its surface millions or billions of years ago.
But now researchers at the University of Michigan say small amounts of liquid water could form on the planet today - despite its below-freezing temperatures.
To come to the conclusion they created chambers that mimic the conditions on Mars, and found that they were able to make liquid water form for brief periods of time.
Researchers at the University of Michigan have created the conditions on Mars to show that liquid water can exist on its surface - for brief periods of time. Here PhD student and researcher Erik Fischer sets up the Mars Atmospheric Chamber in the Space Research Building
Liquid water is an essential ingredient for life as we know it, and Mars is one of the very few places in the solar system where scientists have seen promising signs of it.
EVIDENCE OF WATER ON MARS
Evidence of water on Mars dates back to the Mariner 9 mission, which arrived in 1971. It revealed clues of water erosion in river beds and canyons as well as weather fronts and fogs.
Viking orbiters that followed caused a revolution in our ideas about water on Mars by showing how floods broke through dams and carved deep valleys.
Mars is currently in the middle of an ice age, so liquid water cannot exist on its surface at the present time. However, the planet seems to have been warmer and wetter in the past.
In June last year, Curiosity found Powerful evidence that water good enough to drink once flowed on Mars. In September, the first scoop of soil analysed by Curiosity revealed that fine materials on the surface of the planet contain two per cent water by weight.
This includes gullies down crater rims, instrument readings and in self-portraits taken by the Phoenix lander several years ago that appeared to show wet beads on the lander's leg.
No one has directly detected liquid water beyond Earth, though; the U-M experiments are among the first to test theories about how it could exist in a climate as cold as that on Mars.
The researchers found that a type of salt present in Martian soil can readily melt ice it touches - just like salts do on Earth's slippery winter walkways and roads.
'For me, the most exciting thing is that I can now understand how the droplets formed on the Phoenix leg,' said Dr Nilton Renno, a professor of atmospheric, oceanic and space sciences who led the research.
In 2008, Dr Renno was the first to notice strange globules in photos Phoenix sent back.
Over several weeks, the globules seemed to grow and coalesce.
While Dr Renno deemed them water and suggested that salts on the planet's surface might make it so, many of his colleagues disagreed. Salts had never been found on Mars.
But then they were. Among those that Phoenix detected is calcium perchlorate, a mixture of calcium, chlorine and oxygen that's found in arid places like the Atacama Desert in Chile.
Years later, the Curiosity rover found it elsewhere on Mars. Now scientists believe it and other salts are sprinkled across the planet's surface.
In 2008, Dr Renno was the first to notice strange globules in photos Nasa's Phoenix lander sent back from Mars. Over several weeks, the globules seemed to grow and coalesce. He deemed them water and suggested that salts on the planet's surface might make it so, which has now been confirmed
Nasa's stationary Phoenix lander touched down on the surface of Mars on 25 May 2008. It was the first successful landing in a Martian polar region and remained operational until November 2008, during which time it dug into the ground to research the history of water on Mars
In the case of Phoenix, Dr Renno believes the craft's landing thrusters blasted away the topsoil, exposing the ice and melting it.
That formed muddy saltwater that splashed on the lander's leg as it touched down in the northern polar region.
The salts allowed the droplets to remain liquid. Their existence and stability, Renno says, tipped scientists off to a cycle that doesn't need always need help from an Earth-borne spacecraft.
The U-M researchers recreated the Phoenix landing site conditions in their lab in metal cylinders two feet (0.6 metres) high and five feet (1.5 metres) long.
The late Martian spring and early summer temperatures in the chambers ranged from -120 to -20°C (-185 to -5°F).
Atmospheric pressure hovered around 1 per cent of Earth's while relative humidity varied, but for most experiments it was set to 100 per cent.
This image shows the team's successful attempt to create water in a Mars-like environment. On the left is salt by itself, during which time no water formed. If salt was placed on top of water ice, however, as shown on the right, they found that liquid water was able to form
They tested two scenarios: salt by itself and salt on top of water ice.
In the salt-only experiments, they put millimeter-thick layers of salt on a temperature-controlled plate to simulate Mars-like soil.
Even after more than three hours, no liquid water formed.
When the researchers placed salty soil directly on ice three millimetres (0.12 inches) thick, however, drops of liquid water formed within minutes when the chambers reached -73°C (-100°F).
That is well within the range of conditions observed at the Phoenix landing site.
The findings show how small amounts of liquid water could exist across a large swath of Mars' surface and shallow subsurface, from its polar regions to its mid-latitudes, for several hours a day during the spring and early summer.
Such a cycle could form gullies, Dr Renno says, that flow, freeze, thaw and flow again. Water could also form just beneath the surface.
The chamber simulates the atmospheric conditions of Mars, usually at -50°C/-50°F (shown), in hopes of producing water through the interaction of salt with the atmospheric conditions simulated by the chamber. The resulting research allows Astrobiologists to postulate about the potential of life on Mars
Dr Renno says the water wouldn't necessarily need to stay liquid indefinitely for it to support microbial life now or have supported it in the past, and even just a tiny droplet of water is enough for bacteria to grab hold of and survive.
'Mars is the planet in our solar system that is most similar to Earth,' added Erik Fisher, first author on the new paper and doctoral student in the epartment of Atmospheric, Oceanic and Space Sciences (AOSS).
'Studies suggest that Mars used to be even more Earth-like in the past, with flowing water on the surface.
'By studying the formation of liquid water on Mars we can learn about possibilities of life outside Earth and look for resources for future missions.'
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