Abstract

When a comet nears the Sun, volatile materials near the surface of its nucleus sublimate, releasing gas, which carries dust grains into space that are pushed away from the Sun by the pressure of sunlight alone. The gaseous atoms and molecules are ionized through several processes. The ions then join the solar wind that flows outwards from the Sun, and are visible as the comet’s ion tail. In this presentation, the formation, appearance, and structure of both ion and dust tails will be covered. Much of what has been learnt about these tails derives from unexpected tail crossings by spacecraft not targeted at comets, sometimes occurring at huge distances from the comets’ heads. An overview of these unexpected crossings will be provided, and how more of these events are being sought. Finally, the proposed Comet Interceptor mission is presented. If approved, this European Space Agency project will involve an encounter with a comet nearing the Sun for the first time since the solar system’s formation. If a suitable target is found, the spacecraft could even visit an interstellar object. The talk will be followed by refreshments outside the lecture theatre. The talk will be at 7:30pm at the usual location of Wolfson lecture theatre in the Department of Chemistry. The entrance is the opposite side of the building to Bristol-Myers-Squibb Lecture theatre and is opposite the car park- shown by the red arrow on the map. https://map.cam.ac.uk/Department+of+Chemistry#52.197964,0.125242,18 Tickets are £2 (free for members) and annual membership (£7) and life membership (£12) can also be purchased at the event – please bring cash.