Scientists at Nasa have discovered evidence that briny water flows on Mars during its warmest months, raising chances that life could exist on the Red Planet.
Recently analysed images from the United States space agency’s Mars Reconnaissance Orbiter satellite show dark, finger-like features that extend down some slopes and crater walls on the planet during its late spring and summer, fading in the Martian winter.
On board the satellite was a device developed by Bern University’s Space Research and Planetary Sciences Division that enabled the Swiss – the only European team involved – to analyse the light in images taken by a special camera.
“These dark features grow and fade on a yearly cycle,” physicist Nicolas Thomas told swissinfo.ch.
“There are numerous possible explanations for that, but we’ve basically come to the conclusion that it has to be water trapped as ice. In spring the sun comes up and melts the ice, the water then flows down a 40-degree slope making the surface dark. That then fades away as you go towards winter as the stuff evaporates and freezes.”
Thomas, a professor at Bern’s Space Research and Planetary Sciences Division, also said scientists were aware of the existence of salts in several places on Mars.
“Salt, as we know from our own experience of chucking it on the roads in winter, tends to sink the freezing point of water. This is why we think these flows are actually a sort of a salty brine mix,” he said.
This would explain why it would not freeze in the planet’s frigid surface temperatures, which can fall to around minus 128 degrees Celsius, or evaporate in its low air pressure.
“So all of this is pointing towards it being liquid water. The difficulty that we’ve got is that we don’t have a spectrometer that can look for water absorption lines that’s been good enough to detect the water directly.”
Best evidence yet
Nasa first found signs of water on Mars more than a decade ago, but earlier indications were that any existing water would be frozen and concentrated at the poles.
“This is the best evidence we have to date of liquid water occurring on Mars,” said Philip Christensen, a geophysicist at Arizona State University and member of a Nasa panel that announced the findings in Washington.
The scientists on Nasa’s panel stressed that liquid water is more likely to sustain life than ice, underscoring the importance of the latest discovery.
Past Nasa discoveries revealed evidence of ancient shorelines and riverbanks on Mars. An analysis of gullies on the Red Planet five years ago turned up fresh mineral deposits that suggested recent water flows but provided no categorical proof of that, scientists said.
Another possibility to account for the periodic darkening in the areas under examination is dust moving along the surface of the planet, said Alfred McEwen of the University of Arizona, Tucson, lead author of a report on evidence of water flows published on Thursday in the journal Science.
But dust avalanches would occur at more random intervals, rather than on a seasonal basis, he said.
Life on Mars?
Scientists on the panel said the latest imaging evidence of flowing water also suggests the existence of liquid water closer to the planet’s equator than previously found.
Any liquid water would likely lie beneath the surface because the atmosphere on Mars is so thin that liquid water above ground would quickly evaporate, they said.
Some organisms on Earth thrive underground with little access to sunlight, and the same thing could be occurring on Mars, said Lisa Pratt, a biogeochemist at Indiana University and participant on the Nasa panel.
Pratt said further research was needed at the seven sites where recurring evidence of flowing water was found.
“It’s our first chance to see an environment on Mars that might allow for the expression of an active biological process, if there is present-day life on Mars,” she said.
Hunt for proof
Swiss media have been getting very excited about the discovery, with tabloid Blick asking on its frontpage whether our grandchildren would be living on Mars. Nicolas Thomas, however, admits to having doubts.
“I’m a sceptic. Some journalists get a bit upset with me because I say ‘be careful’,” he said.
“In this particular case it’s a really interesting result – it’s a really good result – and I’m 80 per cent convinced it’s liquid water, but there’s something sitting in the back of your head saying it just could be that our imagination inside our team isn’t good enough to envisage the process that’s taken place.”
For him, the next step is “clearly nailing down the proof”.
“For the 2016 ExoMars Trace Gas Orbiter mission [see link] we’ve got a couple of experiments that could go some way to solving the riddle,” he said.
“In particular you’d be interested in finding out whether you could see enhanced amounts of water vapour directly above these sites during the summer so you could see the stuff actually boiling off locally,”
Mars is the fourth planet from the sun in the solar system. Its distance from Earth varies greatly, but in 2003 the two planets were separated by a mere 55 million kilometres.
The good news:
The Martian day (24 hours 39 minutes) is very close to Earth's.
Mars has a surface area that is 28.4% of Earth's, only slightly less than the amount of dry land on Earth (29.2% of Earth's surface).
Mars has an atmosphere. While very thin (about 0.7% of Earth's atmosphere), it provides some protection from solar and cosmic radiation.
On the other hand:
The surface gravity on Mars is only a little more than one third that of Earth's. It’s not known whether this level is high enough to prevent the health problems associated with weightlessness.
Mars is much colder than Earth, with an average surface temperature of -63 degrees Celsius and a low of -140.
There are no standing bodies of liquid water on the surface of Mars.
swissinfo.ch and agencies