A screengrab from animation of the Martian poles with ice caps.
Now, the big question for a lot of people will be: If this probe is so old... why are we just now figuring this out?
"This is the place on Mars where you have something that most resembles a habitat, a place where life could subsist", said planetary scientist Roberto Orosei of Istituto Nazionale di Astrofisica in Italy, who led the research published in the journal Science.
Between May 2012 and December 2015, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (or "MARSIS" for short) surveyed the region of Mars known as the Planum Australe, a 200-kilometer area on the planet's southern polar plain, which is composed of water ice, Carbon dioxide ice, and admixed dust.
Artistic impression of the Mars Express spacecraft probing the southern hemisphere of Mars. The study area is highlighted using a THEMIS IR image mosaic. Credit: USGS ASTROGEOLOGY SCIENCE CENTER, ARIZONA STATE UN. Although they pass relatively unscathed through most substances, these pulses reflect back up to the spacecraft each time they encounter boundaries between different materials, such as the interface of ice and bedrock.
Between May 2012 and December 2015, Dr. Cicchetti and colleagues used MARSIS to survey a region called Planum Australe, located in the southern ice cap of Mars. It isn't 100% certain, but it's likely that they really have found a pocket of liquid water - either a cluster of underground pools, or a layer of liquid water mixed in with the soil.
They spent at least two years examining the data to make sure they'd detected water, not ice or another substance. That's because it's well below the freezing point of water; the only thing stopping it from turning to ice is a mix of toxic salts. "The problem is that this water is located 1.5km underneath the South Pole, so there is an terrible lot of ice to be drilled to before you reach this liquid water", he added.
So, how did MARSIS find this lake?
Several years into the mission, MARSIS scientists began to see small, bright echoes under the south polar ice cap-so bright that the reflection could indicate not just rock underlying the ice, but liquid water. The depth of the water is not known.
Mars’s southern polar ice cap
Lakes might even turn up at lower, warmer latitudes-a location more suitable for a martian microbe, says Valèrie Ciarletti of the University of Paris-Saclay, who is developing a radar instrument for Europe's ExoMars rover, due to launch in 2020. The radar cross section has been tilted 90°. This strong radar reflection was interpreted by the study's authors as liquid water - one of the most important ingredients for life in the Universe.
"The presence of a body of liquid water beneath Mars's south polar cap has various implications, opening new possibilities for the existence of microorganisms in the Martian environment", says Sebastian Lauro, a study co-author based at Roma Tre University in Rome. With the stunning findings, that debate is likely to be put to bed.
Finding that much water could be a great signpost in our search for life on Mars, but the results should be taken with a grain of salt.
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. There have even been reports of ice being locked up deep below the Mars surface. But Clifford holds out hope subsurface geothermal hotspots like those that power volcanoes and hot springs on Earth could sufficiently heat portions of the Martian underworld to allow liquid reservoirs to exist there without the need for life-sabotaging salt levels.
Michael Meyer believes the more we study Mars, the more we will learn how life could be supported and where there are resources to support life in the future.
There is another satellite orbiting Mars right now, but it hasn't detected what MARSIS did.
Needless to say, the findings reported by the MARSIS team are incredibly exciting, despite my cautious reporting.
"It will require flying a robot there, which is capable of drilling through 1.5 kilometres of ice", he explained.
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