The answer to one of the questions that has greatly puzzled scientists for years comes from the great depths of the Antarctic glaciers: the presence of water on the Red Planet. An international study carried out by researchers from Italy, USA, UK and Hong Kong and led by the Glaciology group at the University of Milano-Bicocca (Giovanni Baccolo, Barbara Delmonte, and Valter Maggi) has enabled the identification, for the first time, of the formation of the mineral jarosite (hydrous sulphate of iron and potassium) at great depths in Antarctic glaciers. This result confirms the hypothesis that the jarosite-rich sediments detected on the surface of Mars by NASA’s Rover Opportunity are related to the presence of large ice caps that covered part of the red planet in the ancient geological past. The results of the study have been published in the “Nature Communications” journal (“Jarosite formation in deep Antarctic ice provides a window into acidic, water-limited weathering on Mars”).
The discovery of extensive jarosite deposits on Mars was a key scientific achievement at the time because the formation of this mineral requires the presence of liquid water; it was still unclear, however, how these deposits were created. One of the possible explanations, consistent with the size and characteristics of these deposits, predicts that there are large, dust-rich ancient ice caps on Mars in different regions of the planet. Today this hypothesis was directly confirmed for the first time by the study conducted at the University of Milano-Bicocca’s EUROCOLD LAB Glaciology laboratory, in close collaboration with the NASA Houston Laboratory (USA), the Diamond Light Source synchrotron (UK), the National Institute of Nuclear Physics, the University of Roma Tre and the University of Hong Kong.
Through the joint application of several cutting-edge analytical techniques (X-ray absorption spectroscopy, X-ray fluorescence, and scanning and transmission electron microscopy), the formation of jarosite crystals was observed in the deepest part of the ice core drilled at the Talos Dome site (East Antarctica). This drilling, directed by Professor Massimo Frezzotti of the Department of Science at Roma Tre University, reached a depth in the ice of over 1600 meters, spanning a time interval of at least 300,000 years. The ice core was recovered between 2004 and 2007 as part of the Italian-led TALDICE project (www.taldice.org), funded by the European Union with the support of the National Research Program in Antarctica.
The researchers showed that the mechanism that could explain the formation of jarosite at Talos Dome is the chemical and mineralogical transformation of mineral dust trapped in the deep ice, at a depth of over 1000 metres where the temperature is about -10°C. Under these conditions, the liquid water necessary for the precipitation of jarosite is present in the form of concentrated acid solutions whose freezing point is much lower than the freezing temperature of pure water.
“The TALDICE drilling ice samples,” explains Massimo Frezzotti, “in addition to reconstructing the climate of the last 300,000 years, have allowed us to hypothesize the climatic conditions of Mars in the distant past.”
“The discovery,” says Giovanni Baccolo, “will revolutionize how we interpret the origin of the widespread deposits containing jarosite on Mars. Although they have now disappeared, it appears that the ancient Martian glaciers and the mineral dust trapped within them have left an evident geological trace on the Red Planet, testifying to climatic events that occurred in the remote past.”