Back in 2018, scientists reported the discovery of a huge lake of liquid water below the ice sheet of the south pole of Mars. A new research has now refuted this hypothesis and called it a 'mirage'.
Is there liquid water under the polar caps of Mars?
Some landforms on Mars, such as river beds and lake beds, indicate that there was once water on the surface of the planet. A small amount of water is still present in the thin Martian atmosphere, and the poles of Mars are covered with ice caps.
The first assumption about the presence of liquid water under the polar caps of Mars appeared about 30 years ago. However, it has not yet been possible to confirm or refute them, just as it has not been possible to detect stable accumulations of liquid water on Mars. There is enough frozen water on Mars: for example, in 2016, a frozen lake was found at a depth of up to 10 meters under the Utopia plain.
In 2018, researchers reported that they had discovered a subglacial reservoir with a diameter of about 20 kilometers at the south pole of Mars – they claimed it was the first convincing evidence of the presence of water in a liquid state on the planet.
The team used the MARSIS radar aboard the European Mars Express orbiter for observations from May 2012 to December 2015. It surveyed the 200-kilometer region of the Southern Plateau (Planum Australe), a relatively flat and topographically unremarkable region of the Martian south pole.
On 29 images, they were able to detect an area where the radar signal changed dramatically – for the instrument, this place looks about the same as the subglacial lakes of Greenland and Antarctica.
The authors of the study believed that the object they found is a layer of liquid water at a depth of about 1.5 kilometers. Scientists estimate the diameter of the reservoir at 20 kilometers, the resolution of the instrument is not enough to accurately outline its contours. Its depth is at least several tens of centimeters.
Theoretically, the increase in the signal that the lake is suspected of could result in a layer of frozen carbon dioxide or simply low-temperature water ice, but the authors rejected these assumptions, as these options do not agree well with observational data.
Although the temperature in the lake is most likely negative, scientists suggested that the water in it is liquid – as on Earth, impurities in the water and the pressure of the ice mass can reduce its freezing point.
NASA’s Mars lander “Phoenix” found magnesium, calcium, and sodium perchlorates in the soil at the north pole – the presence of these compounds, firstly, supports the hypothesis of liquid water under polar ice and, secondly, explains why it does not freeze.
New research, published on January 24, 2022, argues that the existence of present-day Martian groundwater is a mirage.
Scientists refuted the hypothesis for a subsurface lake on Mars
Here is what researchers said about their recent work:
“For water to be maintained so close to the surface, not only is a very saline environment needed, but also a strong local heat source. However, this does not correspond to what we know about this region. Our conclusion that the hypothetical lake is actually buried volcanic rock seems the most plausible.”
The south polar mirage dissipated when scientists “covered” Mars with an imaginary global ice sheet and simulated its radar map. The simulation showed what the landscape of the Red Planet would look like if Mars Express looked at it through a 1.5-kilometer layer of ice.
Then, by comparing feature profiles across Mars with those found under the south polar cap, scientists noticed the same bright reflections but scattered across all latitudes. At the same time, they coincided with the location of the volcanic plains.
“On Earth, iron-rich lava flows can leave behind structures that similarly reflect radar. Or perhaps we see mineral deposits in dry riverbeds. In any case, finding out what they are could answer important questions about the history of Mars,” concluded Cyril Grima, lead author of the study from the Institute of Geophysics at the University of Texas (USA).
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Sources:
• Carpineti, D. A. (2022, January 24). Those underground liquid lakes on Mars may have been just a Mirage. IFLScience.
• Crane, L. (2022, January 24). Mars ‘lake’ may actually be volcanic rocks buried beneath the ice cap. New Scientist.
• Grima, C., Mouginot, J., Kofman, W., Hérique, A., & Beck, P. (2022, January 24). The basal detectability of an ice‐covered Mars by marsis. AGU Journals.
• Orosei, R., Lauro, S. E., & Pettinelli, E. (2018, July 25). Radar evidence of subglacial liquid water on Mars. Science.
• Panagopulos, C. (2022, January 24). Hope for present-day martian groundwater dries up. UT News.
