Planetary atmosphere observation analysis

Abstract:

<jats:title>Abstract</jats:title> <jats:p>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 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 600) channels showing the emissions of CH<jats:sub>4</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>6</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>4</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>6</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>8</jats:sub>, C<jats:sub>4</jats:sub>H<jats:sub>2</jats:sub>, HCN, HC<jats:sub>3</jats:sub>N, and CO<jats:sub>2</jats:sub>. 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 <jats:italic>μ</jats:italic>m 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 <jats:italic>μ</jats:italic>m range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 <jats:italic>μ</jats:italic>m 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 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 1500–3500). We also highlight gaps in the current spectroscopic knowledge of molecular bands, including candidate trace species such as C<jats:sub>60</jats:sub> and detected trace species such as C<jats:sub>3</jats:sub>H<jats:sub>6</jats:sub>, that could be addressed by theoretical and laboratory study.</jats:p>

Abstract:

Uranus and Neptune, the Ice Giants, are the unique planets in the Solar System that have not received a dedicated mission. However, studying these planets is crucial for understanding the formation and evolution of our planetary system and the outer systems, for which the ice planet systems are very common.Our current knowledge comes from Earth and space telescope limited observations and from the brief encounter with the Voyager 2 spacecraft almost three decades ago. The recent decadal survey [1] has established a flag mission to Uranus as the following strategic priority for the Nasa exploration program (apart from the ongoing missions to Mars and Europa). From ESA&#8217;s perspective, the outcomes from the Voyage 2050 [2] are also in alignment, recommending the agency&#8217;s participation in a future mission in a collaboration framework, as established in previous successful partnerships like Cassini-Huygens.Several reference missions have been proposed during the last decade [3-4], most of them suggesting an orbiter plus a descent probe configuration. For the orbiter, the scientific priorities should be to study the planet's bulk composition and internal structure, magnetic field, atmosphere circulation, rings, and satellite system. In the case of the descent probe, its primary mission should be to obtain the atmospheric noble gas abundances, noble gas isotope ratios, and the thermal structure of the atmosphere using a mass spectrometer and a meteorological package.Understanding the thermal structure and dynamics of Uranus&#8217; atmosphere requires studying the vertically distributed aerosols (hazes and clouds) and their microphysical and scattering properties. Indeed, aerosols affect the absorption and reflection of solar radiation, directly affecting the energy balance that drives the planet. In this work we present a lightweight radiometer, as a part of the descending probe, dedicated to studying Uranus&#8217;s aerosols. The principle of measurement is based on the vertical variation of the solar radiance at different wavelengths and geometries of observations as the probe falls using photodetectors, field-of-view masks, and interferential filters. From these observations, information on the vertical structure of clouds and hazes, particle size, or scattering properties could be derived.The radiometer takes its heritage from previous missions for Mars exploration [7-9] where its technology has demonstrated its endurance for extreme environments of operation, using limited resources in terms of power consumption, mass and volume footprints, and data budget. These characteristics make this instrument a valuable complementary probe&#8217;s payload for studying Uranus&#8217; atmosphere with a high scientific return.&#160;[1] Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032.&#160; [2] Linda J. Tacconi, Christopher S. Arridge, et al, Voyage2050 Final recommendations from the Voyage 2050 Senior Committee. [3] Christopher S. Arridge, et al.. 2012. [4] Sushil K.AtreyaaMark, et al.,2019 [5] Ian J. Cohen et al 2022 P [6] Athul Pradeepkumar Girija.&#160; 2023&#160;[7] I. Arruego et al. 2017. [8] Apestigue, V. et al 2022 [9] P&#233;rez-Izquierdo, J., Sebasti&#225;n et al, 2016.

Abstract:

We present first results from the James Webb Space Telescope (JWST) observations of Uranus, which provide the first spatially resolved, infrared spectra of the planet&#8217;s atmosphere spanning from 1.66 to 28.6 &#181;m. We evaluate these unprecedented JWST NIRSpec (1.66&#8211;3.05 &#181;m, 2.87&#8211;5.14 &#181;m) and MIRI (4.9-28.6 &#956;m) spectra in the context of existing observations and questions concerning Uranus&#8217; stratospheric chemistry and thermal structure [1].Owing to its frigid atmospheric temperatures, Uranus&#8217; infrared spectrum is extremely weak. Much of the spectrum has never been spatially resolved before, while some had never been clearly observed at all.From the ground, spatially resolved observations of Uranus&#8217; mid-infrared emission are limited to imaging observations targeting the brighter regions of the infrared spectrum (i.e. ~13 &#181;m emission from stratospheric acetylene, and 17-25 &#181;m from the H2 continuum). Images from the Very Large Telescope VISIR instrument at 13 &#181;m show a stratospheric structure distinct to Uranus, with elevated radiance at high latitudes. The physical nature of this structure&#8211;-whether produced by chemical or thermal gradients&#8211;-is unclear given previously available data [1]. From space, the Spitzer Space Telescope observed Uranus' mid-infrared spectrum between ~7 and 36 &#181;m, but it lacked the spatial resolution necessary to resolve potential thermal and chemical structure across the disk [2].Now, with its exceptional sensitivity and outstanding spatial and spectral resolution, JWST reveals Uranus&#8217; stratospheric temperature and chemistry with exquisite new detail, placing new constraints on hydrocarbon abundances and temperature structure across the disk.With a projected lifetime of over a decade, JWST promises to continue providing exciting new insights into the atmospheric structure, composition, and variability of the ice giants for years to come.[1] Roman, M.T, et al. "Uranus in northern..." AJ 159.2 (2020): 45.[2] Rowe-Gurney, N., et al. "Longitudinal variations..." Icarus 365 (2021): 114506.