AOPP Seminar - What's going on inside Uranus (and Neptune)?

Uranus and Neptune have so far only been briefly visited by the Voyager 2 spacecraft, so much remains to be understood about these worlds. In this talk I will consider two open questions: 1) what constraints can we put on the internal structure; and 2) what constraints can be placed upon the external flux of material and space environment. The atmosphere acts as an interface between the interior and the external environment, so by studying the composition using spectroscopy we can infer constraints on both these open questions. I will focus on observations from the Herschel Space Telescope SPIRE and HIFI instruments which provide the most accurate measurement to-date of stratospheric CO and H2O abundance. These species are key indicators of external and internal fluxes. The implication from these observations is that both Uranus and Neptune have very similar rock-rich interiors with only moderate amounts of ices, suggesting the term 'ice giants' may need revision. I also consider observations from the New Horizons student dust counter instrument that can be used to place additional constraints on the external flux processes. The dust counts and stratospheric H2O abundance should both probe external flux, but are inconsistent at Neptune's orbital distance, suggesting the cometary dust flux at Neptune could have a different make up than predicted by current dynamical models.