Scientists solve mystery of why comets emit X-rays

The research published considers the longstanding scientific question of how comets are able to radiate X-rays. A conundrum that is particularly puzzling, given that such emission is normally associated with very hot objects like the Sun, and comets are among the coldest objects in the Solar System. When comets travel through the Solar System they interact with Solar radiation, the Solar wind and the Solar magnetic field. This produces a visible atmosphere or 'coma' as well as the observed cometary tail, and in some cases, X-rays. These are generated on the Sun-ward side of the comet where the Solar wind impacts the cometary atmosphere, forming a bow shock. To investigate how the X-rays are generated, a team of scientists from 15 institutes, including the Universities of Arizona, Belfast, Copenhagen, Chicago, Lisbon, London, Osaka, Oxford, Paris, Strathclyde, Taiwan, as well as AWE Aldermaston, ETH Zurich, RAL Chilton, , performed experiments at the LULI laser facility in Paris, where they replicated the interaction of the Solar wind with a comet. The Oxford team was led by Professor Gianluca Gregori, Professor Subir Sarkar and Professor Tony Bell, all at the Department of Physics.