Mid-Infrared Mapping of Jupiter's Temperatures, Aerosol Opacity and Chemical Distributions with IRTF/TEXES (1606.05498v2)

Abstract: Global maps of Jupiter's atmospheric temperatures, gaseous composition and aerosol opacity are derived from a programme of 5-20 $\mu$m mid-infrared spectroscopic observations using the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA's Infrared Telescope Facility (IRTF). Image cubes from December 2014 in eight spectral channels, with spectral resolutions of $R\sim2000-12000$ and spatial resolutions of $2-4^\circ$ latitude, are inverted to generate 3D maps of tropospheric and stratospheric temperatures, 2D maps of upper tropospheric aerosols, phosphine and ammonia, and 2D maps of stratospheric ethane and acetylene. The results are compared to a re-analysis of Cassini Composite Infrared Spectrometer (CIRS) observations acquired during Cassini's closest approach to Jupiter in December 2000, demonstrating that this new archive of ground-based mapping spectroscopy can match and surpass the quality of previous investigations, and will permit future studies of Jupiter's evolving atmosphere. We identify mid-infrared signatures of Jupiter's 5-$\mu$m hotspots via simultaneous M, N and Q-band observations, which are interpreted as temperature and ammonia variations in the northern Equatorial Zone and on the edge of the North Equatorial Belt (NEB). Equatorial plumes enriched in NH$_3$ gas are located south-east of NH$_3$-desiccated `hotspots' on the edge of the NEB. Comparison of the hotspot locations in several channels across the 5-20 $\mu$m range indicate that these anomalous regions tilt westward with altitude. Aerosols and PH$_3$ are both enriched at the equator but are not co-located with the NH$_3$ plumes. We find hemispheric asymmetries in the distribution of tropospheric PH$_3$, stratospheric hydrocarbons and the 2D wind field. Jupiter's stratosphere is notably warmer at northern mid-latitudes than in the south in both 2000 and 2014. [Abridged]

Mid-Infrared Mapping of Jupiter's Atmosphere Using IRTF/TEXES Observations

This paper provides a comprehensive paper of Jupiter's atmospheric composition, temperature, and aerosol opacity derived from the mid-infrared spectroscopic observations carried out using the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA’s Infrared Telescope Facility (IRTF). The authors have utilized spectral imaging from December 2014 across eight mid-infrared channels to construct three-dimensional maps of Jupiter's tropospheric and stratospheric temperatures, as well as two-dimensional maps of upper tropospheric aerosol opacity, phosphine (PH$_3$), ammonia (NH$_3$), ethane (C$_2$H$_6$), and acetylene (C$_2$H$_2$). This investigation not only reaffirms the dynamic nature of Jupiter's atmosphere but also provides new insights that complement prior findings from spacecraft and ground-based observations.

Methodology

The paper leverages the TEXES instrument's capacity to produce high-resolution spectral maps in the mid-infrared range (5-20 μm) and utilizes spatially-resolved spectra to examine the variation in the measurement of temperatures and composition. Calibration issues due to variable sky transparency and thermal background, which are intrinsic challenges of ground-based observations, were identified and systematically addressed by comparing results against synthetic spectra produced from Cassini Composite Infrared Spectrometer (CIRS) observations acquired during Cassini’s closest approach to Jupiter in December 2000.

Key Findings

1. Temperature Variability: The TEXES observations revealed notable spatial variability in Jupiter's tropospheric and stratospheric temperatures, such as the presence of cold polar vortices beyond ±60° latitude. These features strengthen prior observations by indicating enhanced radiative cooling driven potentially by polar aerosols.
2. Composition Distribution: The mapping shows marked contrasts in aerosol opacity and gaseous components between belts and zones, with the equatorial zones typically showing higher values in both aerosols and gaseous constituents, like NH$_3$ and PH$_3$, indicative of dynamic atmospheric mixing and chemical processes.
3. Wave Activity and Atmospheric Dynamics: Observations suggest the presence of complex equatorial dynamics characterized by plumes and hotspots. The paper notes a westward tilt of these features with altitude, which has implications for understanding the vertical shear of Jupiter's atmospheric waves.
4. North-South Asymmetry: The paper uncovers north-south asymmetries in tropospheric PH$_3$ distribution and stratospheric hydrocarbon abundances, potentially driven by hemispheric differences in mechanical forcing and wave dynamics rather than seasonal changes given Jupiter’s small axial tilt.
5. Comparison with Historical Data: The variability between the TEXES observations (2014) and Cassini data (2000) supports theories regarding the temporal variability in Jupiter’s atmospheric structure, particularly in relation to the quasi-quadrennial oscillation (QQO) affecting equatorial stratospheric temperatures and winds.

Implications and Future Directions

The paper underscores the importance of continuous ground-based spectroscopy in the complement of spaceborne observations for planetary atmospheric sciences. The TEXES program has demonstrated its utility as a means of bridging observational gaps between major space missions, allowing for monitoring of atmospheric changes over time. Future analyses could benefit from enhanced calibration methods and the integration of TEXES data with emerging data from Juno and subsequent missions to refine models of Jupiter’s atmospheric dynamics and chemistry. Additionally, leveraging larger telescopes for higher spatial resolution observations could elucidate finer details of the atmospheric phenomena described.

Overall, this paper is a significant contribution to the understanding of Jupiter's atmospheric processes, providing critical details on the vertical and horizontal distributions of temperature and chemical species, and highlighting the potential for longitudinal atmospheric patterns and their underlying causes.