Solar system

Abstract:

Venus is home to thousands of volcanoes, with a wide range of volumes and sizes. Its surface is relatively young, with a temperature of approximately 735 K and an atmosphere of 92 bar. Past and possible ongoing volcanic outgassing is expected to provide a source to the sustenance of this massive atmosphere, dominated by CO2 and SO2. The lower atmosphere can be investigated in the near-infrared transparency windows on the nightside, such as the 2.3μm thermal emission window, which provides a chance of detection of species with volcanic origin, such as water vapor. The Planetary Spectrum Generator was used to simulate the nightside 2.3μm thermal emission window of Venus. We simulated the effect of a volcanic gas plume rising to a ceiling altitude, for species such as H2O, CO, OCS, HF and SO2. The sensitivity of the radiance spectrum at different wavelengths was explored as an attempt to qualitatively access detection for future measurements of both ground-based and space-instrumentation. We conclude from our qualitative analysis that for the H2O, CO and OCS plumes simulated there is potential to achieve a detection in the future, given a minimum required signal-to-noise ratio of 50. For SO2 and HF plumes, a higher signal-to-noise ratio would be needed.

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:

Titan, Saturn’s largest satellite, maintains an atmosphere composed primarily of nitrogen (N2) and methane (CH4) that leads to complex organic chemistry. Some of the nitriles (CN-bearing organics) on Titan are known to have substantially enhanced 15N abundances compared to Earth and Titan’s dominant nitrogen (N2) reservoir. The 14N/15N isotopic ratio in Titan’s nitriles can provide better constraints on the synthesis of nitrogen-bearing organics in planetary atmospheres as well as insights into the origin of Titan’s large nitrogen abundance. Using high signal-to-noise ratio (>13), disk-integrated observations obtained with the Atacama Large Millimeter/submillimeter Array Band 6 receiver (211–275 GHz), we measure the 14N/15N and 12C/13C isotopic ratios of acetonitrile (CH3CN) in Titan’s stratosphere. Using the NEMESIS, we derived the CH3CN/13CH3CN ratio to be 89.2 ± 7.0 and the CH3CN/CH313CN ratio to be 91.2 ± 6.0, in agreement with the 12C/13C ratio in Titan’s methane and other solar system species. We found the 14N/15N isotopic ratio to be 68.9 ± 4.2, consistent with previously derived values for HCN and HC3N, confirming an enhanced 15N abundance in Titan’s nitriles compared with the bulk atmospheric N2 value of 14N/15N = 168, in agreement with chemical models incorporating isotope-selective photodissociation of N2 at high altitudes.