Solar system

Abstract:

The Cassini spacecraft observed Titan from 2004 to 2017, capturing key atmospheric features, including the tilt of the middle atmosphere and the formation and breakup of winter polar vortices. We analyze low spectral resolution infrared observations from Cassini’s Composite Infrared Spectrometer (CIRS), which provide excellent spatial and temporal coverage and the best horizontal spatial resolution of any of the CIRS observations. With approximately 4 times higher meridional resolution than previous studies, we map the stratospheric temperature for almost half a Titan year. We determine the evolution of Titan’s stratospheric tilt, finding that it is most constant in the inertial frame, directed 120° ± 6° west of the Titan–Sun vector at the northern spring equinox, with seasonal oscillations in the tilt magnitude between around 2 .° 5 and 8°. Using the high meridional resolution temperature field, we reveal finer details in the zonal wind and potential vorticity. In addition to the strong winter zonal jet, a weaker zonal jet in Titan’s summer hemisphere is observed, and there is a suggestion that the main winter hemisphere jet briefly splits into two. We also present the strongest evidence yet that Titan’s polar vortex is annular for part of its life cycle.

Abstract:

<jats:title>Abstract</jats:title> <jats:p>Using a newly developed ‘holistic’ atmospheric model of the aerosol structure in Uranus’s atmosphere, based upon observations made by HST/STIS, Gemini/NIFS and IRTF/SpeX from 2000 – 2009, we make a new estimate the bolometric Bond albedo of Uranus during this time of A* = 0.338 ± 0.011, with a phase integral of q* = 1.36 ± 0.03. Then, using a simple seasonal model, developed to be consistent with the disc-integrated blue and green magnitude data from the Lowell Observatory from 1950 – 2016, we model how Uranus’s reflectivity and heat budget vary during its orbit and determine new orbital-mean average values for the bolometric Bond albedo of $\overline{A^*} = 0.349 \pm 0.016$ and for the absorbed solar flux of $\overline{P_\mathrm{in}}=0.604 \pm 0.027$ W m−2. Assuming the outgoing thermal flux to be $\overline{P_\mathrm{out}}=0.693 \pm 0.013$ W m−2, as previously determined from Voyager 2 observations, we arrive at a new estimate of Uranus’s average heat flux budget of Pout/Pin = 1.15 ± 0.06, finding considerable variation with time due to Uranus’s significant orbital eccentricity of 0.046. This leads the flux budget to vary from Pout/Pin = 1.03 near perihelion, to 1.24 near aphelion. We conclude that although Pout/Pin is considerably smaller than for the other giant planets, Uranus is not in thermal equilibrium with the Sun.</jats:p>

Abstract:

Saturn’s moon Titan undergoes a long annual cycle of 29.45 Earth years. Titan’s northern winter and spring were investigated in detail by the Cassini–Huygens spacecraft (2004–2017), but the northern summer season remains sparsely studied. Here we present new observations from the James Webb Space Telescope (JWST) and Keck II telescope made in 2022 and 2023 during Titan’s late northern summer. Using JWST’s mid-infrared instrument, we spectroscopically detected the methyl radical, the primary product of methane break-up and key to the formation of ethane and heavier molecules. Using the near-infrared spectrograph onboard JWST, we detected several non-local thermodynamic equilibrium CO and CO2 emission bands, which allowed us to measure these species over a wide altitude range. Lastly, using the near-infrared camera onboard JWST and Keck II, we imaged northern hemisphere tropospheric clouds evolving in altitude, which provided new insights and constraints on seasonal convection patterns. These observations pave the way for new observations and modelling of Titan’s climate and meteorology as it progresses through the northern fall equinox, when its atmosphere is expected to show notable seasonal changes.

Abstract:

The ultramafic and silicic rocks on the lunar surface have played an important role in expanding our knowledge regarding its thermal and magmatic evolution. The surface identification and quantification of these rocks on the global scale can significantly improve our understanding of their spatial extents, relationships and formation mechanisms. Christiansen feature positions using Diviner data have aided in global identification and mapping of relatively silica-rich and silica-poor lithologies on the lunar surface. We have used laboratory thermal infrared spectra of silicic and ultramafic rocks to analyze the variation in Christiansen feature in simulated lunar environment. We have characterized the absolute bulk silica content of the rocks and minerals and their Silica, Calcium, Ferrous iron, Magnesium index. We find that they are linearly correlated to the Christiansen feature despite particle size variations. Furthermore, we find that the Christiansen feature shifts toward longer wavelengths with increase in ilmenite content in the ilmenite-basalt mixtures. We have explored the effect of instrument's spectral band position on the accuracy of the parabolic method that is currently used for the estimation of Christiansen feature position from Diviner data. We find that this method performs poorly for the estimation of the Christiansen feature for ultramafic and silicic rocks and minerals/mineral mixtures. We propose using a machine learning algorithm to estimate the Christiansen feature with higher accuracy for all kinds of silicate compositions on the Moon. This method will lead to increased accuracy in absolute quantification of bulk silicate composition of the lunar surface at varying spatial scales.