Current State of Knowledge of the Magnetospheres of Uranus and Neptune 28 July 2014 Abigail Rymer
[email protected] What does a ‘normal’ magnetosphere look like? . N-S dipole field perpendicular to SW . Solar wind driven circulation system . Well defined central tail plasmasheet . Loaded flux tubes lost via substorm activity . Trapped radiation on closed (dipolar) field lines close to the planet. …but then what is normal…. Mercury Not entirely at the mercy of the solar wind after all . Jupiter . More like its own little solar system . Sub-storm activity maybe totally internally driven …but then what is normal…. Saturn Krimigis et al., 2007 What is an ice giant (as distinct from a gas giant) planet? Consequenses for the magnetic field Soderlund et al., 2012 Consequenses for the magnetic field Herbert et al., 2009 Are Neptune and Uranus the same? URANUS NEPTUNE Equatorial radius 25 559 km 24 622 km Mass 14.5 ME 17.14 ME Sidereal spin period 17h12m36s (retrograde) 16h6m36s Obliquity (axial tilt to ecliptic) -97.77º 28.32 Semi-major axis 19.2 AU 30.1 AU Orbital period 84.3 Earth years 164.8 Earth years Dipole moment 50 ME 25 ME Magnetic field Highly complex with a surface Highly complex with a surface field up to 110 000 nT field up to 60 000 nT Dipole tilt -59º -47 Natural satellites 27 (9 irregular) 14 (inc Triton at 14.4 RN) Spacecraft at Uranus and Neptune – Voyager 2 Voyager 2 observations - Uranus Stone et al., 1986 Voyager 2 observations - Uranus Voyager 2 made excellent plasma measurements with PLS, a Faraday cup type instrument.