A team of scientists says it has new evidence that indicates salty, liquid water exists on Mars — bringing us one step closer to discovering life on the Red Planet.
"Finding liquid water anywhere on Mars is important because we associate the presence of liquid to the possibility of having environments where life could be found," University of Southern Queensland geophysicist Dr Graziella Caprarelli said.
An team of Italian scientists first picked up signs of a giant liquid water lake beneath Mars' south pole in 2018.
Two years later, Dr Caprarelli was part of an international team that found more evidence that a bright radar reflection could be a salty lake below the ice caps.
But other scientists have disputed their published findings.
"Other groups have run experiments to try to figure out what other materials could be responsible for the reflections," Dr Caprarelli said.
Other scientists believe the reflection may have been caused be volcanic rocks, like other reflective patches scattered across Mars.
Researchers from the University of Austin in Texas recently published a paper in Geophysical Research Letters Journal, in which they labelled the image "a dusty mirage", and suggested volcanic rock under ice — and not liquid salty water — was a more plausible explanation for the reflection.
So, in order to address these alternative theories, Dr Caprarelli's team conducted extensive laboratory experiments on samples of clay, saline ice and brines in sub-zero temperatures.
She said the team's findings, published in the latest issue of Science Direct, provided even stronger evidence of the existence of water on Mars.
"It is generally assumed that the temperature at the base of the solar ice cap is less than -73 degrees Celsius and we know that pure water only exists as solid ice at these sub-zero temperatures," she said.
'Exciting discovery'
The reflection that sparked the initial belief that liquid water may exist on Mars was found with the MARSIS, a scientific instrument on the European Space Agency's Mars Express spacecraft.
"The experiments show that brines alone have the properties consistent with the bright reflections measured by the MARSIS," Dr Caprarelli said.
Professor Gretchen Benedix, a cosmic mineralogist and astrogeologist from Perth's Curtin University, said it was an exciting discovery.
"I think in terms of the more we understand what water in variation looks like on Mars, whether it's ice or liquid and what form it's in, whether it's salty or fresh, that feeds into our capability to try and understand how to eventually make it a liveable planet,” Professor Benedix said.
"That's where we get thinking about how water works on Earth, [but when] we go to Mars, we have a different surface, so finding liquid on Mars is a whole lot harder."
'Number of unknowns'
Perth planetary and space scientist Dr Eriita Jones said there was no guarantee of the existence of salty liquid water on Mars.
"There are still a number of unknowns, one of which is the current sub-surface temperature models which predict the temperatures at the base of the polar cap," Dr Jones said.
But Dr Jones said it was not impossible either and, with further research, proof of the existence of life on Mars could be found one day.
"We know that there are hypersaline sub-zero liquid water environments on Earth in the Arctic and Antarctic that are inhabited by active microorganisms," she said.
"Although the chemical characteristics of potential sub-surface brines on Mars are not yet known, it is entirely plausible they could be able to support microorganisms with similar requirements to some extremophiles on Earth."
For Dr Caprarelli's team, comprising scientists from Italy and the United States, there is still much to explore.
They are submitting a case to the European Space Agency to extend Mars Express, the mission to which MARSIS belongs, until the end of 2025 for the purpose of being able to conduct more observations.
"This will give us ample opportunity to continue acquiring data from the south pole, but also from the north polar cap."
