Observations of Planetary Aurorae

J. T. Clarke (University of Michigan)

While people have observed the Earth's northern lights throughout recorded history, it is only since the turn of the century that there has been a significant understanding of the physics by which the impressive auroral displays are produced. Ground-based and satellite data have revealed the basic nature of the Earth's aurora, yet debate continues today on the details of the energy generation mechanism(s) and the regions in the Earth's magnetic field where these operate. Over the past 20 years we have gained new insight into the general nature of planetary aurora through measurements of the auroras on all 4 giant planets, with by far the most energetic (and best-observed) aurora on Jupiter. Jupiter's aurora are 100-1000 times more energetic than the Earth's, the input energy likely dominates the global dynamics of Jupiter's upper atmosphere, and there is a unique interaction with Io whichs produces a persistent localized auroral emission at Io's magnetic footprint in Jupiter's atmosphere. This last feature is similar to mass accretion from a companion star onto a neutron star in "AM Her" binary systems. This talk will present an overview of observations and the physics of planetary aurora, concentrating on the auroras at the Earth and the giant planets.