Lecture for Friends of the RAS: The changing atmospheres of Uranus and Neptune

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FRIENDS LECTURE: Tuesday 25 November, 13:00-14:00 in the RAS Lecture Theatre
The changing atmospheres of Uranus and Neptune
Professor Patrick Irwin The 'Ice Giants' of our solar system, Uranus and Neptune, occupy a unique position in our solar system, lying as they do with mass and radius intermediate between Jupiter and Saturn (the 'Gas Giants') and the terrestrial rocky inner planets. However, prior to their observation by instruments on board Voyager 2 in 1986 and 1989 very little was known of the atmospheres of these distant, dark worlds. We now know that both planets have highly dynamic atmospheres with very strong east-west winds that flow with rates of several hundred metres per second and are retrograde at the equator (i.e. are blowing against the direction of planetary rotation) but strongly prograde at mid-latitudes. Although Uranus seemed almost featureless during the 1986 Voyager 2 flyby, its atmosphere has since been seen to become very much more active leading up to its northern spring equinox in 2007. We now believe that the quiescent nature of its atmosphere in 1986 was due to the flyby of Voyager 2 coinciding with Uranus' southern summer solstice, combined with its enormous obliquity of 98? and an almost complete absence of any residual heat of formation. Currently, Uranus and Neptune are observed regularly with HST and ground-based telescopes using the latest imaging and spectroscopic technologies that challenge even the Voyager observations. Both planets are seen to be highly active and dynamic worlds, with storm clouds appearing and disappearing over timescales of days. Professor Patrick Irwin is a planetary atmospheric scientist with over 20 years' experience in remote sensing of planetary atmospheres from satellite and ground-based observations. His undergraduate and graduate degrees were at Oxford, and he was appointed as a University Lecturer in 1996. His main research interests are 1) Radiative transfer modelling of planetary atmospheres (in the Solar System and exoplanets) using thermal emission and scattering models and 2) Development and application of multivariate retrieval methods. Professor Irwin was a member of the Galileo Near Infrared Mapping Spectrometer (NIMS) team and is a Co-Investigator of the Cassini Composite Infrared Spectrometer (CIRS) and also the Visible Infrared Thermal Imaging Spectrometer (VIRTIS) on both the ROSETTA and Venus Express missions. He was also a Consultant Scientist to the Long Wave Spectrometer team of the Infrared Space Observatory. In addition to space missions, Professor Irwin has an active programme of ground-based near-infrared spectroscopic observations (and interpretation) of the Solar System Giant Planets, using UKIRT, IRTF, Gemini-N, ALMA and VLT, and also has experience of mid-IR ground-based observations. Professor Irwin is the principal author or co-author of over 100 papers published, or in press, in the open literature. The talk will be followed by a wine reception in the Library.