Observations of Jupiter's low-latitude ionosphere: almost-global maps of H3+ temperature and density

Jupiter's auroral regions are powerful and bright, lending themselves to more readily sharing the secrets of the Jovian ionosphere in which they occur. However, the relatively under-studied non-auroral ionosphere of Jupiter is at least as intriguing. In full ground-based maps of Jupiter's ionosphere and using narrow-band images taken in 1995-2000, H3+ emissions were found to be diminished in a sinusoidal like pattern across the entire planet. This "ribbon" is found to run almost exactly co-aligned with Jupiter's magnetic dip equator - a region where Jupiter's magnetic field runs parallel to the surface. While this coincidence provides a important clues as to the mechanics at play, it remains unknown why H3+ emissions are found to be weaker along it. What we do know is that H3+ emissions only become weaker for two reasons: either a reduced H3+ density or a reduced H3+ temperature, or some combination of both. If the reason for the diminished emissions is a lower density, this suggests a reduction in the ionization rate; alternatively, if the cause is related to low temperatures, this could mean that Jupiter's low-latitude ionospheric heating source (which is also unknown) is being interrupted for some reason. We endeavor in this report to reveal what combination of temperature and density diminution is occurring using spectroscopic observations taken with the Keck telescope in 2016. These Keck observations will show new "almost global" maps of H3+ temperatures and densities of Jupiter for the first time at high spatial resolution ( 10 degree longitude/latitude), and hopefully provide more clues as to how the ribbon is formed.