Friday 10 Feb 2023: Magnetospheric dynamics and auroras at the outer planets and exoplanets
Johnathan Nichols - University of Leicester
Newman Red 12:30-13:30
Planetary magnetospheres each provide natural laboratories for studying space plasmas, and auroras are "TV screens" that reveal the energetic processes occurring within a magnetosphere. Jupiter possesses the brightest auroras in the solar system, over a thousand times brighter than the Earth's. For over two decades, the standard theory to explain the main auroral emission on Jupiter was as a result of the planet's fast rotation, coupled with emission of many hundreds of kg per second of sulphur and oxygen from the volcanic moon Io. This material is propelled away from Jupiter by the rapidly rotating planetary magnetic field, and as it does so its rotation rate slows due to conservation of angular momentum. Jupiter attempts to keep the material rotating at its rotation rate via a system of electric currents flowing through the planet's ionosphere and magnetosphere, which transfer momentum to the magnetospheric plasma. The electric current flowing out of the planet's atmosphere was thought to drive the auroras, however when Juno arrived at Jupiter, little evidence of an electric current system was reported and the above scenario was questioned. In this talk we discuss the theory of Jupiter's magnetosphere-ionosphere coupling, and compare more recent Hubble Space Telescope observations of the brightness of the main aurora with Juno observations of the amount of current flowing in the magnetosphere. We will go on to examine how theories relating to Earth's and Jupiter's auroral emissions have been applied to objects out of the solar system, e.g. brown dwarfs and exoplanets, and we discuss the detectability of the auroral radio emissions from such objects.