Liquid water on Mars! Lake discovered under Martian ice cap
Meteorologist/Science Writer
Wednesday, July 25, 2018, 10:00 AM - After decades of trying to answer the question of whether Mars has liquid water, scientists appear to have found the answer, and the implications of their discovery could be huge.
Depending on where and how you look, you can find plenty of water on Mars.
Satellites and telescopes have shown us ice deposits at the planet's polar regions. Orbiters have also revealed immense glaciers residing just under the surface, potentially accessible to any future explorers or even colonists that go there in the future. Robotic landers and rovers have uncovered evidence that there were once flowing streams and rivers on the surface, and even freshwater lakes that would have been safe for us to drink.
All of that water is either locked up in solid form, however, or locked away in the distant past.
What about liquid water, on Mars, right now, giving us some possibility that the Red Planet could harbor life?
Based on new research, published in the journal Science on Wednesday, there really is liquid water on Mars - a 20-kilometre-wide lake of it, at least a metre deep, buried under a kilometre-and-a-half of south polar ice!
"We discovered water on Mars," says Roberto Orosei, a researcher with the Italian National Institute for Astrophysics (INAF).
According to Orosei, who led the team that made this discovery, they detected the lake using a ground-penetrating radar instrument on the European Space Agency's Mars Express orbiter, known as the Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS.
Artistic impression of the Mars Express spacecraft probing the southern hemisphere of Mars, superimposed to a color mosaic of a portion of Planum Australe. The study area is highlighted using a THEMIS IR image mosaic. Subsurface echo power is color coded and deep blue corresponds to the strongest reflections, which are interpreted as being caused by the presence of water. Credits: USGS Astrogeology Science Center, Arizona State University, ESA, INAF.
From May 2012 to December 2015, the spacecraft made 29 passes over this one region on Mars, allowing the research team to scan the area with MARSIS, and then combine those scans into a profile of the layers under the surface.
"MARSIS was able to detect echoes from beneath the southern polar cap of Mars, that were stronger than surface echoes," Orosei explained. "This condition on Earth happens only when you observe subglacial water, like in Antarctica, over places like Lake Vostok."
Lake Vostok is a persistent lake of freshwater, some 4 kilometres below the surface of the East Antarctica ice sheet. The lake is very likely warmed from below by geothermal heat, while at the same time is insulated from the cold at the surface by the ice itself. This keeps the lake at just below freezing temperatures, and it maintains a liquid state due to the immense weight of the ice above pressing down on it.
In the case of this subsurface lake of water on Mars, the researchers say that it is likely stays liquid partly due to magnesium, calcium and sodium salts, which are common in Mars rocks. This would lower the water's freezing temperature, and combined with the pressures exerted by the 1.5 kilometres of ice above it, it would be prevented from freezing solid.
Watch below as Roberto Orosei walks us through this amazing discovery:
DETECTING A SUBSURFACE LAKE FROM SPACE
So, how did MARSIS find this lake?
Geophysicist Cassie Stuurman, who was not involved in this particular discovery, but who did discover the Lake Superior-sized glacier under Mars' surface, reported back in 2016, explained that the way ground penetrating radar works is by sending out radio waves, and then measuring the return waves that are reflected off the surface, and off boundaries between different materials under the surface.
"So, if there's a boundary between air and ice, or ice and dust, or ice and water, we get a reflection back," Stuurman said.
The reason for the reflections at these boundaries has to do with the electrical properties of the materials, and according to Stuurman, liquid water has radically different electrical properties than rock or ice.
"It sticks out like a sore thumb in the radar data," she said.
Artistic impression of the Mars Express spacecraft probing the southern hemisphere of Mars. A radar cross section of the southern polar layered deposits is shown as a detail. The radar cross section has been tilted 90°. The rightmost white line is the surface radar echo, while the light blue spots along the basal radar echo highlight areas of very high reflectivity, interpreted as being caused by the presence of water. Credit: Credits: ESA, INAF. Graphic rendering by Davide Coero Borga – Media INAF
"What the paper found is a region in the south polar layered deposits with unusually high reflective properties," Stuurman explained. "And when they modelled the electrical properties of this region, using what we know about radar reflections and different Martian materials, they found a result that is consistent with the presence of liquid water."
Even more to the point, Stuurman said that - based on what the satellite measured - there is no other likely alternative explanation for the detection, other than liquid water.
HUGE IMPLICATIONS
There is, and probably will continue to be, debate about the findings of this paper, simply because the implications of this discovery are immense.
"It's an exciting discovery, if it's true," said Tanya Harrison, Professional Martian and Director of Research for Arizona State University's Space Technology and Science Initiative, who was also not involved in this discovery, "since we know that life can survive in subglacial lakes, and brine pockets inside glaciers, here on Earth."
Indeed, scientists have found bacteria and other simple forms of life living in these kinds of extreme environments on our own planet, which use chemical reactions with salts and minerals to get the energy they need to live.
There is already speculation about the presence of these 'extremophiles' in the salty subsurface oceans discovered inside some of the icy moons in our solar system. Data from NASA's Cassini orbiter, even though the mission ended in 2017, continues to provide researchers with evidence of organics under the ice of Saturn's moon Enceladus, although they can't yet tell if geology or biology produced those organics (Cassini simply wasn't equipped to give scientists what they need to tell the difference).
This discovery of a salty subsurface lake, on an object much closer to the Sun, and much larger than a moon, is even bigger news.
There is already ample evidence that Mars likely had an environment that would have been friendly to life as we know it, long in the past.
This, however, is the best evidence to date of an environment on Mars that could be friendly to known forms of life - these 'extremophile' bacteria - right now.
To know for certain if this lake actually exists is not going to be easy, Orosei says. Right now, they have a subsurface radar detection, where the very best interpretation from experts in the field is that it comes from some form of liquid water. Verifying that result, beyond any shadow of a doubt, however, will take more.
"It will require flying a robot there, which is capable of drilling through 1.5 kilometres of ice," he explained. "This will certainly require some technological developments that, at the moment, are not available."
