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One of the countless unsolved mysteries about the red planet is why ancient Mars had liquid water. At the beginning of the planet’s history, Mars only received a third of today’s Earth’s sunlight, which shouldn’t be enough heat to hold water. But in ancient millennia, huge rivers flowed across the planet’s surface, when its atmosphere was denser and warmer, cutting through ravines and canals in the silent and desolate landscape, unchanged for millions of years that are visible today to spaceships in orbit. Scientists have long known that water was abundant on ancient Mars, but there has been no consensus on whether liquid water was common or whether it was largely frozen in ice.
In 2013, planetary scientists from the European Space Agency released 3D images of the surprising upper part of the Reull Vallis region of Mars, revealing a 1,500-kilometer-long river running from the Promethei Terra Highlands to the vast Hellas Basin. Image data from ESA’s Mars Express spacecraft shows that, at some points, the riverbed is seven kilometers wide and 300 meters deep. Stereo cameras on board the satellite have also revealed “numerous tributaries” that feed the gigantic river. The current low atmospheric pressures on the red planet mean that the surface water would evaporate. But recent discoveries reveal that water does not survive frozen in polar caps and underground ice deposits, but also in a massive network of ancient buried lakes.
Mars in a Billion – “Rainstorms and Huge Flowing Rivers”
In January 2020, Caltech astronomers probed a mysterious feature at the South Pole of Mars: a massive deposit of CO2 ice and water ice in alternating layers, like layers of a cake, shown on top of the page, which extend to a depth of one kilometer, buried under a thin layer of CO2 ice. This strange feature was preceded in 2018 by the discovery of evidence suggesting that deep below the deeply frozen ice sheet at the south pole of Mars is a lake of liquid water, the first to be found on the Red Planet. Detected from orbit using the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) ice-penetrating radar, the finding resembles interconnected bodies of water buried under several kilometers of ice in Greenland and Antarctica, where it has been detected. a network of 400 lakes.
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MARSIS, an instrument on the European Space Agency’s Mars Express orbiter, which was launched in 2003, emits pulses of radio waves and listens for reflections. Some of the waves bounce off the surface, but others penetrate up to 3 kilometers and can be reflected by abrupt transitions in buried layers, such as going from ice to rock.
Several years after the mission, MARSIS scientists began to see small, bright echoes under the South Pole ice sheet, so bright that the reflection could indicate not just rocks under the ice, but liquid water. However, the researchers doubted that the signal was real because it appeared in some orbital passes but not others.
“Ice Age Mars”: challenge a red planet that was once ‘hot and humid’
The spacecraft’s computer was averaging pixels to reduce the size of large data streams and, in the process, smoothing out bright anomalies. “We weren’t seeing what was right under our noses,” says Roberto Orosei, MARSIS Principal Investigator (PI) at the Italian National Institute for Astrophysics in Bologna.
“It’s a very exciting result – the first indication of a brackish aquifer on Mars,” said geophysicist David Stillman of the Southwest Research Institute in Boulder, Colorado. The findings, if confirmed, would mark the detection of the largest mass of liquid water on Mars, Marina Koren reported in The Atlantic.
Huge lake detected under the south pole of Mars: “We weren’t seeing what was right under our noses”
A lake of liquid water surrounded by smaller ponds may be buried under 1,400 meters of ice near the south pole of Mars, Nature reports. New measurements offer more evidence for its existence, according to Elena Pettinelli of the Roma Tre University in Italy and her colleagues who used the MARSIS radar instrument and then applied criteria that were used to search for buried lakes in Greenland, where new research has increased the number of known lakes lurking beneath the ice sheet from just four to a total of 60, to survey an area called Ultima Scopuli near the South Pole of the Red Planet.
The researchers saw a liquid lake measuring about 20 by 30 kilometers, along with at least three smaller ponds, each a few kilometers wide. But the resolution of the radar measurements was not high enough to determine its depth.
“It was probably originally a larger wet area, and this is the remnant of that in smaller ponds,” says Pettinelli. For the water to remain liquid at cold temperatures, his team suggests that it is most likely a salty brine.
“There are bacteria that can live in very uncomfortable situations,” says Pettinelli. “In Antarctica, they found bacteria living happily in underground lake water and among ice crystals, and Antarctica is our closest analog to Mars.”
The Daily Galaxy through science, nature, new scientists, the Atlantic
Image credit at the top of the page: The ice-covered Martian South Pole, represented here by the Mars Express spacecraft that also carries the MARSIS radar instrument. (ESA / DLR / FU Berlin / Bill Dunford)
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