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Séminaire du jeudi 14 septembre 2017

The spring magnetosphere of Uranus

Laurent Lamy (LESIA)
Thursday September 14th - 11am
IRAM Seminar Room - IRAM

The redetection of ultraviolet Uranus’ aurorae with the Hubble Space Telescope (HST) in 2011, 4 years past equinox and during episodes of active solar wind, opened a new window in the study of the asymmetric Uranian magnetosphere, so far restricted to the single observations of Voyager 2 which flew by the planet in 1986. The atypical geometry of the magnetosphere (60° tilt between the rotation and magnetic axes) make it particularly sensitive to solar wind conditions (strength and orientation), over timescales ranging from a planetary rotation (17.24h) up to seasonal variations (a Uranian revolution lasts for 84 years). The auroral features identified in 2011 were hot spots with short lifetimes, possibly produced by magnetic reconnexion between the planetary and interplanetary magnetic fields on the dayside magnetopause. In this seminar, I will present the results of more recent HST observations of Uranus’ aurorae, obtained in 2012 and in 2014 during quiet and active solar wind conditions, predicted in advance with several MHD propahation models. These observations reveal new auroral detections, whose properties both resemble and differ from those of 2011 and suggest a major role of solar wind in driving auroral precipitations. The longitudinal fit of the 2014 data also enabled us to retrieve the longitude of magnetic poles, lost since 30 years.

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CNRS Université Grenoble Alpes