Solar system

Abstract:

Jupiter’s Oval BA undergoes recurrent colour changes whose physical origin remains uncertain. Radiative transfer retrievals indicate that these changes occur in the upper chromophore haze of the vortex annulus, around and above the 0.2–bar level, and are primarily associated with a decrease in optical depth, with no significant change in particle size or haze altitude. We apply a one-dimensional microphysical model to this haze layer, constrained by the retrieved aerosol properties of the red annulus in 2016 and the whiter annulus in 2020, and use it to reproduce the observed colour-change timescale of approximately 0.5 years. Our results indicate that this transition is best reproduced by changes in tropospheric vertical transport within a subsiding annulus, corresponding to preferred downwelling velocities of order 10−4–10−3 m s−1 at chromophore-bearing pressures. These small vertical velocities may help explain why no clear dynamical signature has yet been identified.

Abstract:

Abstract The Hubble Space Telescope collected imaging data spanning the full lifetime of Neptune's dark spot NDS‐2018, which is the sixth large, persistent dark spot seen in the planet's atmosphere. Neptune's dark spots are thought to be anticyclonic vortices, although internal flows have never been directly measured to confirm their rotation. Previous reports covered the formation and evolution of the mature NDS‐2018, while here we report that the contrast weakened over the 2021 to 2022 period, while the feature rapidly drifted equatorward from 14 deg N to 6–7 deg N planetographic latitude. The persistence of the spot so close to the equator is surprising, and represents a challenge for numerical models which find anticyclones to be disrupted within 15 deg of the equator. The changing contrast of the dark spot constrains changes in the aerosols over time, but the link between dynamical and microphysical properties of dark vortices is not known.

Abstract:

Cassini observed Jupiter during its 2000–2001 gravity-assist flyby, acquiring a valuable set of Visible and Infrared Mapping Spectrometer (VIMS) observations over a wide range of viewing geometries and observing conditions. These data comprise visible and infrared spectral cubes covering the VIS channel from 0.35 to 1.05 µm and the IR channel from 0.9 to 5.1 µm. We present a calibrated catalog of these Jupiter VIMS observations,  excluding satellite-targeted observations, designed to provide a homogeneous and validated set of spectral products for future Jovian studies.Starting from the raw archive cubes, we developed a processing workflow that combines ISIS/SPICE-based geometry recovery with dedicated radiometric calibration procedures for both VIMS channels. The final products are delivered as multi-extension FITS files containing calibrated I/F spectral cubes, wavelength and FWHM vectors, and geometry backplanes for incidence, emission, and phase angles, planetocentric latitude, positive-east longitude, pixel resolution, and azimuth angle. The workflow also addresses several issues affecting the original data set, including saturation, VIS pointing-related offsets between radiometric cubes and geometric backplanes, channel-dependent dark-signal artifacts, and a subset of IR approach-phase for which the standard ISIS calibration pipeline can produce over-scaled reflected spectra.The resulting catalog provides a uniform, documented, validated, and publicly available set of Cassini/VIMS Jupiter products. By combining calibrated VIS and IR cubes with wavelength information and geometry backplanes, these products facilitate a wide range of applications in the study of Jupiter and its atmosphere.

Abstract:

JWST-NIRSpec observations are providing our first detailed view of the Ice Giants in the 5-micron spectral window [1]. Observations of Jupiter and Saturn (see Figure) at 5 microns have historically revealed important insights into their tropospheric composition, along with striking images of clouds silhouetted against the glowing thermal emission from deeper atmospheric layers [2]. Comparable observations of the colder Ice Giants, however, have long remained beyond observational reach—until now.In this talk, we present JWST-NIRSpec 5-micron observations of the Ice Giants and discuss their implications. We examine what these observations reveal about the tropospheric temperatures, clouds, and composition of Uranus and Neptune, as well as what they may imply for current radiative transfer models at these wavelengths.In particular, we find that the JWST data may suggest sub-adiabatic temperature gradients near the cloud layers, resulting in colder temperatures in the deeper atmosphere. However, these conclusions depend sensitively on the scattering properties of Ice Giant clouds and on accurate modelling of the gaseous opacity, both of which, we argue, remain uncertain under these conditions.Figure: Saturn at 5 microns (left, in red) from Cassini, with hazes shown in green (Image credits: NASA/JPL-Caltech/University of Arizona), compared to Uranus at 5 microns from JWST-NIRSpec [1].[1] Roman, M.T., et al., The Infrared Spectrum of Uranus Revealed with JWST (submitted)[2] Wong, M.H., Bjoraker, G.L., Goullaud, C., Stephens, A.W., Luszcz-Cook, S.H.,1047Atreya, S.K., Pater, I., Brown, S.T.: Deep clouds on jupiter. Remote Sensing104815(3), 702 (2023)