On the origin and evolution of the material in 67P/Churyumov-Gerasimenko

International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects

The role of the thymus in multiple sclerosis

The presence of numerous changes in T lymphocyte activity found in MS patients points to the involvement of the thymus in multiple sclerosis. The etiophathogenetic mechanism of MS is probably an autoimmune reaction that is triggered by a viral infection caused by one or more viruses and that perpetuates itself, causing the disease to progress. It has been proved that the thymus maintains its immunocompetence even in adulthood and that it has a role in the pathogenesis in several autoimmune diseases. In exacerbations of MS there is a decrease in T suppressor lymphocytes while histological and lymphocyte subset changes have been demonstrated in the thymus of MS patients. The lymphocyte response to mitogens is also depressed in MS. The clinical results of thymectomy in MS are not uniform and are on the whole inconclusive, probably through the lack of criteria of selection of patients for surgical treatment. We consider that the morphological and functional study of the thymus biopsy specimen should supply the appropriate criteria of suitability for surgical treatment