Rosie E. Johnson

Cassini VIMS observations of H3+ emission on the nightside of Jupiter

We present the first detailed analysis of H3+ nightside emission from Jupiter, using Visual and Infrared Mapping Spectrometer (VIMS) data from the Cassini flyby in 2000–2001, producing the first Jovian maps of nightside H3+ emission, temperature, and column density. Using these, we identify and characterize regions of H3+ nightside emission, compared against past observations of H3+ emission on the dayside. We focus our investigation on the region previously described as “mid-to-low latitude emission,” the source for which has been controversial. We find that the brightest of this emission is generated at Jovigraphic latitudes similar to the most equatorward extent of the main auroral emission but concentrated at longitudes eastward of this emission. The emission is produced by enhanced H3+ density, with temperatures dropping away in this region. This emission has a loose association with the predicted location of diffuse aurora produced by pitch angle scattering in the north, but not in the south. This emission also lays in the path of subrotating winds flowing from the aurora, suggesting a transport origin. Some differences are seen between dayside and nightside subauroral emissions, with dayside emission extending more equatorward, perhaps caused by the lack of sunlight ionization on the nightside, and unmeasured changes in temperature. Ionospheric temperatures are hotter in the polar region (~1100–1500 K), dropping away toward the equator (as low as 750 K), broadly similar to values on the dayside, highlighting the dominance of auroral effects in the polar region. No equatorial emission is observed, suggesting that very little particle precipitation occurs away from the polar regions.

The Great Cold Spot in Jupiter's upper atmosphere

Abstract Past observations and modeling of Jupiters thermosphere have, due to their limited resolution, suggested that heat generated by the aurora near the poles results in a smooth thermal gradient away from these aurorae, indicating a quiescent and diffuse flow of energy within the subauroral thermosphere. Here we discuss Very Large Telescope‐Cryogenic High‐Resolution IR Echelle Spectrometer observations that reveal a small‐scale localized cooling of ~200 K within the nonauroral thermosphere. Using Infrared Telescope Facility NSFCam images, this feature is revealed to be quasi‐stable over at least a 15 year period, fixed in magnetic latitude and longitude. The size and shape of this “Great Cold Spot” vary significantly with time, strongly suggesting that it is produced by an aurorally generated weather system: the first direct evidence of a long‐term thermospheric vortex in the solar system. We discuss the implications of this spot, comparing it with short‐term temperature and density variations at Earth.

Jupiter's polar ionospheric flows: High resolution mapping of spectral intensity and line‐of‐sight velocity of H3+ ions

We present a detailed study of the H3+ auroral emission at Jupiter, which uses data taken on the 31 December 2012 with the long-slit echelle spectrometer CRIRES (ESO-VLT). The entire northern auroral region was observed using significantly more slit positions than previous studies, providing a highly detailed view of ionospheric flows, which were mapped onto polar projections. Previous observations of ionospheric flows in Jupiters northern auroral ionosphere, using the long-slit echelle spectrometer CSHELL (NASA-IRTF) to measure the Doppler shifted H3+ ν2 Q(1,0-) line at 3.953 μm, showed a strongly sub-rotating region that was nearly-stationary in the inertial magnetic frame of reference, suggesting an interaction with the solar wind. In this work, we observe this stationary region coincident with a polar region with very weak infrared emission, typically described as the dark region in UV observations. Although our observations cannot determine the exact mechanisms of this coupling, the co-incidence between solar wind controlled ionospheric flows and a region with very low auroral brightness may provide new insights into the nature of the solar wind coupling. We also detected a super-rotating ionospheric flow measured both at and equatorward of the narrow bright portion of the main auroral emission. The origin of this flow remains uncertain. Additionally, we detect a strong velocity shear poleward of the peak in brightness of the main auroral emission. This is in agreement with past models which predict that conductivity, as well as velocity shear, plays an important role in generating the main auroral emission.

The quest for H-3(+) at Neptune: deep burn observations with NASA IRTF iSHELL

This work was supported by the UK Science and Technology Facilities Council (STFC) Grant ST/N000749/1 for HM and TSS. LNF was supported by a Royal Society Research Fellowship at the University of Leicester. REJ and PTD were supported by STFC studentships. Support for JO’D. comes from an appointment to the NASA Postdoctoral Program at Goddard Space Flight Center, administered by Universities Space Research Association under contract with NASA. LM was supported by NASA under Grant NNX17AF14G issued through the SSO Planetary Astronomy Program. HM, REJ, and TSS are Visiting Astronomers at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration.

Mapping H3+ Temperatures in Jupiter's Northern Auroral Ionosphere Using VLT‐CRIRES

We present a detailed study of the H3 auroral emissions at Jupiter, using data taken on 31 December 2012 with the long-slit Echelle spectrometer CRIRES (ESO-VLT). From this data set the rotational temperature of the H3 + ions in Jupiter’s upper atmosphere was calculated using the ratio of the ν2 Q(1,0 !) and ν2 Q(3,0 !) fundamental emission lines. The entire northern auroral region was observed, providing a highly detailed view of ionospheric temperatures, which were mapped onto polar projections. The temperature range we derive in the northern auroral region is ~750–1000 K, which is consistent with past studies, although the temperature structure differs. We identify two broad regions which exhibit temperature changes over a short period of time (~80 minutes). We propose that the changes in temperature could be due to a local time change in particle precipitation energy, or they could be caused by dynamic temperature changes generated in the neutral thermosphere due to the magnetospheric response to a transient enhancement of solar wind dynamic pressure, as predicted by models. By comparing the H3 + temperature, column density, total emission, and line-of-sight velocity, we were unable to identify a single dominant mechanism responsible for the energetics in Jupiter’s northern auroral region. The comparison reveals that there is complex interplay between heating by impact from particle precipitation and Joule heating, as well as cooling by the H3 + thermostat effect. Plain Language Summary This study focuses on Jupiter’s northern lights (aurora) and the temperature of the molecules which create them. A charged molecule, H3 , which exists in Jupiter’s upper atmosphere, emits at infrared wavelengths. Using the Very Large Telescope, situated in Chile, we can observe Jupiter’s infrared aurora. The telescope has an instrument that splits up the wavelengths of the aurora, creating spectra fromwhich we can calculate the temperature, column density, and total emission of Jupiter’s upper atmosphere. The whole polar region is observed, and maps of these parameters were created. By comparing these parameters, as well as the velocity of the charged molecules, which were calculated in our previous study, we can investigate the heating and cooling processes of Jupiter’s upper atmosphere. This study is the first to measure temperature differences in Jupiter’s aurora over short periods of time. These temperature changes could be caused by variations that happen during Jupiter’s day or they could be caused by the response of Jupiter’s magnetic field to a process external to the Jupiter system.