From Earth to Mars: mineralogical and geochemical perspective from NASA’s rovers and from a recent discovery in the Aeolian Arc, Sicily

In the last decades, the Martian NASA’s rovers produced an enormous amount of data, in the terms of high-resolution images, chemical and mineralogical composition of the martian soils and rocks. Interesting for mineralogists and geochemists are the Mössbauer data acquired by Spirit and Opportunity, and XRDP carried out by Curiosity. In addition, all the rovers are equipped with an APXS instrument (Alpha-Particle X-Ray Spectrometer) for bulk analysis and a microscopic imaging camera. The collected data re-reading, however, highlights some anomalies. Pyroxenes, olivines and magnetite represent the most diffuse mineral phases besides hematite, goethite and nanophase oxyhydroxides. The average sulfur content in rocks and soils, in the range of 7 %, can reach the remarkable value of 40 %. Most of the identified mineral phases could be closely associated to hydrothermalism. In addition, spherical particles similar in composition to terrestrial ooids have been photographed by all the rovers in some of the detected areas such as Gale Crater (Curiosity), Meridiani Planum (Opportunity) and Gusev Crater (Spirit). For instance, at Meridiani Planum crossed by Opportunity Rover, the soil appears discontinuously covered by iron-rich spherules resembling iron ooids. Here we report, the wide iron-ooids deposit recently discovered off Panarea Island, located on an active submarine hydrothermal system recognised as the responsible for their formation. Emphasis is placed on linking geometric properties to physical mechanisms. The recent terrestrial iron-ooids are millimetre-concentric depositions of primary cryptocrystalline goethite on pre-existing sediment/skeletal particles. Hydrothermal fluids composed of a mixture of thermal waters and CO2-dominated gases vented through the seafloor sediments acted as supplier of iron and builders of the laminated structure due to agitation of loose sediment particles. In this scenario, we provide new insights into the origin of the spherical-grains-bearing deposits of Mars for which several genetic hypotheses (including those involving biological activities) have been proposed. The exceptional recently iron ooid deposit discovered in the SE Tyrrhenian Sea, represents an excellent natural laboratory to relate a hydrothermal system and vents, that on Mars might have harboured life, with structures and mineral compositions that on the surface of Mars seem to be widespread.