Tuesday 21 September at 2:30pm

Steve Miller - UC London

"The Role of H3+ in Planetary Atmospheres"

ABSTRACT: "In the decade since its first detection in the auroral regions of Jupiter, the fundamental molecular ion H3+ has been used to probe the physical and chemical properties of the upper atmospheres of the outer planets. There it is formed either by high energy particle precipitation or by solar EUV ionisation of the predominantly molecular hydrogen atmosphere. H3+ is thus a sensitive probe of energy inputs and coupling between planets and their magnetospheres. "H3+ emits strongly in the infrared: in the L and L' windows in particular, its fundamental vibrational spectrum has many strong transitions; in the K window, the overtone spectrum is a high temperature diagnostic. Thus the Mauna Kea observatories - especially UKIRT, IRTF and CHFT - have led the world in H3+ studies of the planets. "Jupiter is by far the most studied of the outer planets; infrared H3+ imaging has proved essential to improving models of the planet's giant magnetic field. This talk, however, will concentrate on what has been learned from spectroscopic studies using CGS4 on UKIRT and CSHELL on the IRTF. It will discuss the implications of temperature, column density and emission results for the thermal balance of the upper atmosphere. "Recent results show that H3+ spectroscopy can be an important probe of the dynamics of the atmosphere. High velocity ionospheric winds may prove to be the key to identifying missing energy sources which account for the unusually high jovian temperature. UCL's Jovian Ionosphere Model (JIM) and the results of simulating high energy ionosphere/thermosphere inputs will be discussed in the light of new dynamic models. "Uranus and Saturn are much less studied. But they show how each of the planets is unique in terms of its H3+ activity (as is the case with so many other of their properties). And we will speculate on the possibility that H3+ may hold the key to directing planets outside of our own solar system directly."