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© Lucie DELAUCHE / Cécile ENGRAND / Jean DUPRAT / IJCLab / IMPMC / CNRS Photothèque
Particles of cosmic dust from comets or asteroids, known as micrometeorites, have always fallen on our planet. Some of these are spherules, micrometeorites that have totally or partially melted on entering the atmosphere. The spherule shown here has a diameter of 170 micrometres. Its surface reveals pale-coloured, dendritic (tree-like) crystals of magnetite that formed as a result of the interaction of the molten meteorite with oxygen in the atmosphere as it solidified. This cosmic dust grain is just one of some 5 200 tonnes of micrometeorites that reach the Earth’s surface every year. Studying this dust, which was collected in central Antarctica near the French-Italian Concordia Station, sheds new light on how our star and its planets formed, 4.5 billion years ago.