More than 15 years ago, the Mars Express probe identified gigantic deposits beneath the Medusae Fossae formation, considered the largest source of dust on Mars. At that time there were doubts about their composition. New observations in 2022 show that these deposits are actually made of water ice, making them the largest amount of water ever found in this part of the planet.
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More than 15 years ago, the European Space Agency's (ESA) Mars Express probe observed the Medusae Fossae formation at the planet's equator. This region of Mars is considered to be the largest sediment deposit on the planet. It stretches discontinuously for more than 5,000 kilometers and covers an area equivalent to the area of India. It consists of several wind-sculpted geological structures hundreds of kilometers in diameter and several kilometers high. These formations lie on the boundary between the highlands and lowlands of Mars and are probably the largest source of dust on Mars and one of the most extensive deposits on the planet.
Enigmatic nature of the deposits beneath the Medusae Fossae Formation
Radar data at the time showed massive deposits up to a depth of 2.5 kilometers. However, the data was not clear enough to determine exactly what it consisted of. Although it was thought that these could be ice deposits, scientists did not rule out that they were actually huge accumulations of dust, volcanic ash or wind-blown sediment.
In 2023, the same team observed this fascinating region of Mars again. She came to a conclusion that leaves little doubt about the nature and composition of these subterranean deposits.
Using new Marsis radar data, scientists discovered that the Medusae Fossae deposits were “even thicker than previously thought: up to 3.7 kilometers thick,” says Thomas Watters of the Smithsonian Institution, lead author of both studies. He added that it is “interesting to note that the radar signals are consistent with what we expect from ice layers and are similar to the signals we see from the polar ice caps of Mars, which we know to be very rich in ice “. The new results instead suggest layers of dust and ice, all covered by a protective layer of dry dust or ash several hundred meters thick.
Gigantic amounts of water
We're talking about a gigantic amount of ice. If all of the trapped ice were to melt, it would actually cover the entire planet with a layer of water 1.5 to 2.7 meters high: the largest amount of water ever found in this part of Mars, and enough to fill Earth's Red Sea to fill. This new data also casts doubt on the 2007 conclusions. Given the thickness of the deposits beneath Medusae Fossae, we would expect that they would collapse under their own weight if they were just giant piles of dust, volcanic ash, or wind-blown sediment. ” says co-author Andrea Cicchetti of the Italian National Institute of Astrophysics. This would create something much denser than what we actually see at MarsisMarsis. And when we modeled the behavior of various materials without ice, nothing could mimic the properties of the Medusae Fossae Formation : We need ice cream. »
Implications and new themes in the history of the water cycle on Mars
Although Mars appears to be a barren world today, the planet's surface is full of signs that water was once plentiful, including dry river channels, ancient sea and lake beds, and valleys carved by water. “Water.” We also discovered significant reserves of water ice on Mars, such as the giant polar ice caps, buried glaciers closer to the equator, and near-surface ice embedded in the Martian soil.
Not surprisingly, this latest analysis “challenges our understanding of the formation of Medusae Fossae and raises as many questions as answers,” says Colin Wilson, ESA scientist on the Mars Express missions and the Trace Gas Orbiter. If they were water ice, “these massive deposits would transform our understanding of Mars' climate history and would be a fascinating target for human and robotic exploration of Mars.” For those who want to find out where the water that flowed on the Mars flowed, these deposits are part of the answer!
Although Mars appears dry today, the discovery sparks interest in the planet's past water and raises questions about its climate history. However, these deposits, buried beneath hundreds of meters of dust and sediment, are currently inaccessible and pose a challenge for future research.