PlanetMapper: A Python package for visualising, navigating and mapping Solar System observations

PlanetMapper is an open source Python package to visualise, process and understand astronomical observations of Solar System objects, such as planets, moons and rings. Astronomers can use PlanetMapper to ‘navigate’ observations by calculating coordinate values (such as latitude and longitude) for each pixel in an observed image, and can map observations by projecting the observed data onto a map of the target body. Calculated values are exportable and directly accessible through a well documented API, allowing PlanetMapper to be used for custom analysis and processing. PlanetMapper can also be used to help generate publication quality figures, and has a Graphical User Interface to significantly simplify the processing of astronomical data. PlanetMapper can be applied to a wide range of datasets, including both amateur and professional ground-based observations, and data from space telescopes like Hubble and JWST.  </p

Compositional Mapping of Europa Using MCMC Modeling of Near-IR VLT/SPHERE and Galileo/NIMS Observations

We present maps of surface composition of Europa’s anti-Jovian hemisphere acquired using high spatial resolution IFU multispectral data from the SPHERE instrument on the Very Large Telescope (0.95–1.65 μm) and the NIMS instrument on the Galileo orbiter (0.7–5.2 μm). Spectral modeling was performed using a Markov Chain Monte Carlo method to estimate endmember abundances and to quantify their associated uncertainties. Modeling results support the leading–trailing hemisphere difference in hydrated sulfuric acid abundances caused by exogenic plasma bombardment. Water-ice grains are found to be in the 100 μm–1 mm range, with larger grains present on the trailing hemisphere, consistent with radiation-driven sputtering destroying smaller grains. Modeling best estimates suggest a mixture of sulfate and chlorinated salts, although uncertainties derived from the MCMC modeling suggest that it is difficult to confidently detect individual salt abundances with low spectral resolution spectra from SPHERE and NIMS. The high spatial resolution offered by SPHERE allows the small-scale spatial distribution (<150 km) of potential species to be mapped, including ground-based detection of lineae and impact features. This could be used in combination with other higher spectral resolution observations to confirm the presence of these species.</p

Custom JWST NIRSpec/IFU and MIRI/MRS Data Reduction Pipelines for Solar System Targets

We present custom JWST data reduction pipelines for JWST NIRSpec/IFU and MIRI/MRS observations of solar system objects. The pipelines simplify the process of reducing the JWST observations, and include custom steps to significantly improve the data quality. Our custom processing routines include a "desaturation" routine to reduce the effect of saturation while still maintaining high signal-to-noise ratio, and custom flat field correction code to remove the significant artifacts found in MIRI/MRS observations. The pipelines also automatically generate a series of quick look plots and animations to simplify exploration of a dataset. These custom JWST pipelines can be downloaded from https://github.com/JWSTGiantPlanets/pipelines.</p

Giant Planet Atmospheres: Dynamics and Variability from UV to Near-IR Hubble and Adaptive Optics Imaging

Each of the giant planets, Jupiter, Saturn, Uranus, and Neptune, has been observed by at least one robotic spacecraft mission. However, these missions are infrequent; Uranus and Neptune have only had a single flyby by Voyager 2. The Hubble Space Telescope, particularly the Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) instruments, and large ground-based telescopes with adaptive optics systems have enabled high-spatial-resolution imaging at a higher cadence, and over a longer time, than can be achieved with targeted missions to these worlds. These facilities offer a powerful combination of high spatial resolution, often <0.05”, and broad wavelength coverage, from the ultraviolet through the near infrared, resulting in compelling studies of the clouds, winds, and atmospheric vertical structure. This coverage allows comparisons of atmospheric properties between the planets, as well as in different regions across each planet. Temporal variations in winds, cloud structure, and color over timescales of days to years have been measured for all four planets. With several decades of data already obtained, we can now begin to investigate seasonal influences on dynamics and aerosol properties, despite orbital periods ranging from 12 to 165 years. Future facilities will enable even greater spatial resolution and, combined with our existing long record of data, will continue to advance our understanding of atmospheric evolution on the giant planets.</p

Spitzer IRS Observations of Titan as a Precursor to JWST MIRI Observations

In this work, we present for the first time infrared spectra of Titan from the Spitzer Space Telescope (2004–2009). The data are from both the short wavelength–low resolution (SL; 5.13–14.29 μm, R ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 μm, R ∼ 600) channels showing the emissions of CH4, C2H2, C2H4, C2H6, C3H4, C3H6, C3H8, C4H2, HCN, HC3N, and CO2. We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the 16.35–19.35 μm wavelength range observed by the SH channel but impacted by higher noise levels in the CIRS observations. We use the SH data to provide estimated haze extinction cross sections for the 16.67–17.54 μm range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 μm wavelength range that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument (5.0–28.3 μm, R ∼ 1500–3500). We also highlight gaps in the current spectroscopic knowledge of molecular bands, including candidate trace species such as C60 and detected trace species such as C3H6, that could be addressed by theoretical and laboratory study.</p

Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and Polar Vortices With VLT/VISIR

Using images at multiple mid‐infrared wavelengths, acquired in 2018 May using the Very Large Telescope Imager and Spectrometer (VISIR) instrument on ESO's Very Large Telescope (VLT), we study Jupiter's pole‐to‐pole thermal, chemical and aerosol structure in the troposphere and stratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones and warm cloud‐free cyclonic belts persists throughout the mid‐latitudes, up to the polar boundaries, and evidence a strong correlation with the vertical maximum windshear and the locations of Jupiter's zonal jets. At high latitudes, VISIR images reveal a large region of mid‐infrared cooling poleward ∼64°N and ∼67°S extending from the upper troposphere to the stratosphere, co‐located with the reflective aerosols observed by JunoCam, and suggesting that aerosols play a key role in the radiative cooling at the poles. Comparison of zonal‐mean thermal properties and high‐resolution visible imaging from Juno allows us to study the variability of atmospheric properties as a function of altitude and jet boundaries, particularly in the cold southern polar vortex. However, the southern stratospheric polar vortex is partly masked by a warm mid‐infrared signature of the aurora. Co‐located with the southern main auroral oval, this warming results from the auroral precipitation and/or joule heating which heat the atmosphere and thus cause a significant stratospheric emission. This high emission results from a large enhancement of both ethane and acetylene in the polar region, reinforcing the evidence of enhanced ion‐related chemistry in Jupiter's auroral regions.</p

Radiative-convective models of the atmospheres of Uranus and Neptune: Heating sources and seasonal effects

Context. The observations made during the Voyager 2 flyby have shown that the stratosphere of Uranus and that of Neptune are warmer than expected by previous models. In addition, no seasonal variability of the thermal structure has been observed on Uranus since Voyager 2 era and significant subseasonal variations have been revealed on Neptune. Aims. In this paper, we evaluate different realistic heat sources that can induce sufficient heating to warm the atmosphere of these planets and we estimate the seasonal effects on the thermal structure. Methods. The seasonal radiative-convective model developed by the Laboratoire de Météorologie Dynamique was used to reproduce the thermal structure of these planets. Three hypotheses for the heating sources were explored separately: aerosol layers, a higher methane mole fraction, and thermospheric conduction. Results. Our modelling indicates that aerosols with plausible scattering properties can produce the requisite heating for Uranus, but not for Neptune. Alternatively, greater stratospheric methane abundances can provide the missing heating on both planets, but the large values needed are inconsistent with current observational constraints. In contrast, adding thermospheric conduction cannot warm the stratosphere of both planets alone. The combination of these heat sources is also investigated. In the upper troposphere of both planets, the meridional thermal structures produced by our model are found inconsistent with those retrieved from Voyager 2/IRIS data. Furthermore, our models predict seasonal variations should exist within the stratospheres of both planets while observations showed that Uranus seems to be invariant to meridional contrasts and only subseasonal temperature trends are visible on Neptune. However, a warm south pole is seen in our simulations of Neptune as observed since 2003.</p

Water‐Ice Dominated Spectra of Saturn's Rings and Small Moons From JWST

JWST measured the infrared spectra of Saturn's rings and several of its small moons (Epimetheus, Pandora, Telesto, and Pallene) as part of Guaranteed Time Observation program 1247. The NIRSpec instrument obtained near‐infrared spectra of the small moons between 0.6 and 5.3 microns, which are all dominated by water‐ice absorption bands. The shapes of the water‐ice bands for these moons suggests that their surfaces contain variable mixes of crystalline and amorphous ice or variable amounts of contaminants and/or sub‐micron ice grains. The near‐infrared spectrum of Saturn's A ring has exceptionally high signal‐to‐noise between 2.7 and 5 microns and is dominated by features due to highly crystalline water ice. The ring spectrum also confirms that the rings possess a 2%–3% deep absorption at 4.13 microns due to deuterated water ice previously seen by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft. This spectrum also constrains the fundamental absorption bands of carbon dioxide and carbon monoxide and may contain evidence for a weak aliphatic hydrocarbon band. Meanwhile, the MIRI instrument obtained mid‐infrared spectra of the rings between 4.9 and 27.9 microns, where the observed signal is a combination of reflected sunlight and thermal emission. This region shows a strong reflectance peak centered around 9.3 microns that can be attributed to crystalline water ice. Since both the near and mid‐infrared spectra are dominated by highly crystalline water ice, they should provide a useful baseline for interpreting the spectra of other objects in the outer solar system with more complex compositions.</p

Water‐Ice Dominated Spectra of Saturn's Rings and Small Moons From JWST

JWST measured the infrared spectra of Saturn's rings and several of its small moons (Epimetheus, Pandora, Telesto, and Pallene) as part of Guaranteed Time Observation program 1247. The NIRSpec instrument obtained near‐infrared spectra of the small moons between 0.6 and 5.3 microns, which are all dominated by water‐ice absorption bands. The shapes of the water‐ice bands for these moons suggests that their surfaces contain variable mixes of crystalline and amorphous ice or variable amounts of contaminants and/or sub‐micron ice grains. The near‐infrared spectrum of Saturn's A ring has exceptionally high signal‐to‐noise between 2.7 and 5 microns and is dominated by features due to highly crystalline water ice. The ring spectrum also confirms that the rings possess a 2%–3% deep absorption at 4.13 microns due to deuterated water ice previously seen by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft. This spectrum also constrains the fundamental absorption bands of carbon dioxide and carbon monoxide and may contain evidence for a weak aliphatic hydrocarbon band. Meanwhile, the MIRI instrument obtained mid‐infrared spectra of the rings between 4.9 and 27.9 microns, where the observed signal is a combination of reflected sunlight and thermal emission. This region shows a strong reflectance peak centered around 9.3 microns that can be attributed to crystalline water ice. Since both the near and mid‐infrared spectra are dominated by highly crystalline water ice, they should provide a useful baseline for interpreting the spectra of other objects in the outer solar system with more complex compositions.</p

Super-adiabatic temperature gradient at Jupiter's equatorial zone and implications for the water abundance

The temperature structure of a giant planet was traditionally thought to be an adiabat assuming convective mixing homogenizes entropy. The only in-situ measurement made by the Galileo Probe detected a near-adiabatic temperature structure within one of Jupiter's 5μm hot spots with small but definite local departures from adiabaticity. We analyze Juno's microwave observations near Jupiter's equator (0– 5 oN) and find that the equatorial temperature structure is best characterized by a stable super-adiabatic temperature profile rather than an adiabatic one. Water is the only substance with sufficient abundance to alter the atmosphere's mean molecular weight and prevent dynamic instability if a super-adiabatic temperature gradient exists. Thus, from the super-adiabaticity, our results indicate a water concentration (or the oxygen to hydrogen ratio) of about 4.9 times solar with a possible range of 1.5– 8.3 times solar in Jupiter's equatorial region