At the Origin Of Ceres Phyllosilicates (Planetary Science)

In a study published in Nature Communication – which also involves Marco Ferrari, Maria Cristina De Sanctis and Simone De Angelis of INAF in Rome – the results of laboratory experiments that simulate the physical and chemical environments of Ceres are reported, with the goal of understanding the origin and formation mechanisms of ammonia phyllosilicates present on the dwarf planet

The surface mineralogy of the dwarf planet Ceres is rich in ammonium (NH + ) containing phyllosilicates , i.e. silicates characterized by a tetrahedral symmetrical layered structure, in which each tetrahedron tends to bind with three others via oxygen bridges.

The widespread presence of ammonia phyllosilicates is closely linked to the history of the evolution of the dwarf planet. However, the origin and formation mechanisms of ammonia phyllosilicates on the surface of Ceres are still not well understood.

The ammonia minerals on the surface of Ceres may have originated from the reaction of clay minerals with ammonia (NH 3 ), present in the form of ice or organic matter containing ammonia. These processes may have been triggered by thermal alterations or spatial weathering , through exposure of Ceres’ surface to solar wind and galactic cosmic rays on geological time scales.

Recently, it has been proposed that the formation of ammonium salts on the surface of comets occurs through acid-base reactions induced by thermal processes of ice. Although the surface compositions of comets and that of Ceres are different, a presumably similar heat treatment may have initiated proton transfer reactions, along with nucleophilic addition reactions , during the evolution of Ceres.between ammonia and phyllosilicate clays. Curiously, space erosion could also facilitate the joining of ammonia with minerals to form ammonium ions. However, the lack of fundamental low-temperature laboratory experiments on transforming ammonia-coated minerals into ammonia silicates under realistic Solar System conditions leaves open the question of the source of the spectroscopic signatures of ammonia minerals on Ceres’ surface.

In a study recently published in Nature Communication , which also involves Marco Ferrari , Maria Cristina De Sanctis and Simone De Angelis of the Institute of Space Astrophysics and Planetology of INAF in Rome, the results of laboratory experiments that simulate the physicists and chemists of Ceres, with the aim of better understanding the source of ammonia minerals on the surface of the dwarf planet.

Scientists observed that at low temperatures (54 K) proton exchange reactions between phyllosilicates and ammonia could be triggered, leading to the genesis of ammonia minerals. The study revealed the thermal (300 K) and radiation stability of ammonia phyllosilicates on a time scale of at least about 500 million years .

These experimental investigations confirm the possibility that Ceres formed in a place where the ammonia ice on the surface would have been stable. However, the possibility cannot be ruled out that Ceres’ place of origin approximates its current location, and that it accumulated ammonia-rich material afterwards.«The origin of the presence of ammonium on Ceres is still a matter of debate and several experiments have been conducted to understand the processes that originated the ammonia phyllosilcates. Experiments such as those discussed in this article “, explains Maria Cristina De Sanctis,” indicate an alternative path to the more well-known processes involving the circulation of solutions of water and ammonia. This experiment proposes a process without water in liquid form and suggests a process that is possible not only on Ceres but also on other bodies that are at very low temperatures ».

Featured image: Occator crater on Ceres. Credits: Nasa / Jpl-Caltech / Ucla / Mps / Dlr / Ida

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Provided by INAF

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