Reflectivity of Venus’s Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns

Reflectivity of Venus's Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52-1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283-800 nm wavelengths. Considerable absorption is present in the 350-450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

Atmospheres under fire: The effects of volcanic and impact induced plumes on the atmospheres of Io and Jupiter, respectively.

Atmospheres Under Fire: The Effects of Volcanic and Impact Induced Plumes on The Atmospheres of Io and Jupiter, Respectively provides a detailed description of the by-products derived from these two common Solar System events. Both direct volcanic venting of SO, SO2, S2 gas, and the subsequent freezing and sublimation of the volcanic SO2 output leads to localized Ionian atmospheres. Additionally, transport from either of these localized sources may contribute to the existence of a tenuous extended Ionian atmosphere. Analysis of consecutive disk-integrated near-ultra violet spectra of Io obtained in 1994 and 1996 indicates that Io's atmosphere is characterized by temporally varying localized and global distributions of SO and SO2 gases. These data provide the first measurement of the temporal variability of Io's atmosphere with respect to Io's location relative to the impinging, self-generated plasma torus. They also provide the first measurement of changes in Io's atmosphere within the two hour time period immediately following eclipse egress indicating that SO gas was depleted during eclipse conditions, and that the extended SO and SO2 gas components increased and decreased, respectively. I also present constraints of the SO, SO2, and S2 gas properties over the Pele volcano derived from spatially and spectrally resolved observations of the Pele plume and its deposit region. The collision of the Shoemaker-Levy 9 fragments with Jupiter represents an equally intriguing, fundamental Solar System phenomenon. This collision resulted in impact-induced plumes that rose to elevations ∼1200 km above the 1 bar level of the Jovian atmosphere, and re-entered the collisional region of the Jovian atmosphere ∼20 minutes subsequent to the initial fragment impacts producing ejecta patterns extending ∼60--12,000 km across the Jovian cloud tops. Based on a detailed ballistic analysis of Hubble Space Telescope Wide Field and Planetary Camera 2 images of the impact phenomena resulting from the collision of the Shoemaker-Levy 9 fragments A, E, G and W with Jupiter, I present an accurate definition of the velocities of the impact-induced ejecta. From these results the energy of the impacts and the potential effect of these kinds of collision events within the Solar System can be assessed.Ph.D.AstronomyPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132189/2/3057978.pd

Simulations of Vertical Profiles of SO and SO2 in Venus’ Mesosphere

The primary reservoir for SO2 on Venus lies in the troposphere, but a pronounced SO2 inversion layer has been consistently observed my multiple instruments since modern observations began in 2004. The Caltech/JPL photochemical model with simplified standard chemistry was used to calculate steady-state vertical profiles for SO2 as a function of solar zenith angle at 58–110 km altitude. Assuming photochemistry ceases at each altitude at the solar zenith angle where the photochemical lifetime equals the zonal transport lifetime, an estimate of the actual non-steady-state vertical profile at the evening terminator has been constructed for the equatorial region. The resultant profile has a factor of two increase in the SO2 mixing ratio from 70 to 80 km altitude. This agrees qualitatively but not quantitatively with the observations, which suggests the interaction of photochemistry and dynamics may be important for creating the observed mesospheric SO2 inversion layer

14 N 15 N detectability in Pluto's atmosphere

Based on the vapor pressure behavior of Pluto's surface ices, Pluto's atmosphere is expected to be predominantly composed of N2 gas. Measurement of the N2 isotopologue 15N/14N ratio within Pluto's atmosphere would provide important clues to the evolutio

Atmospheric chemistry on Venus: An overview of unresolved issues

Venus' atm. is 96.5% CO_2 and 3.5% N_2 with trace abundances of SO_2, OCS, H_2O, HCl, HF, and HBr, as well as their photochem. and lightning-induced products. The global clouds are composed at least partly of concd. sulfuric acid. The surface pressure is 90 atm and surface temps. exceed 700 K. Atm. chem. transitions from ion chem. through photochem. to thermal equil. chem. with heterogeneous chem. likely throughout the atm. Three major chem. cycles have been identified: the carbon dioxide, sulfur oxidn., and polysulfur cycles. The carbon dioxide cycle includes CO_2 photolysis, transport of a significant fraction of CO and O to the night side, prodn. of O_2, and conversion of CO and O_2 to CO_2, possibly via chlorine catalyzed pathways. The sulfur oxidn. cycle comprises transport upward of OCS, SO_2, and H_2O, oxidn. to H_2SO_4, condensation to form the global 30-km thick cloud layers, and sulfuric acid rain. The polysulfur cycle involves the upward transport of OCS and SO_2, disproportionation and prodn. of S_x (x=2-8), and downward transport of S_x to react with CO and SO_3. There is solid evidence for the carbon dioxide and sulfur oxidn. cycles; the polysulfur cycle is more speculative but plausible. Alternatively, sulfur chem. on Venus has been conceptually divided into fast and slow atm. cycles and a geol. cycle. Recent work (Parkinson et al, PSS, 2015) suggests the ternary SO_2-H_2O-H_2SO_4 system may bifurcate depending on the relative abundances of H_2O and SO_2. Despite this general understanding, five decades of spacecraft, and 200 years of observation, numerous significant unresolved issues remain. One is the means by which CO_2 is stabilized over geol. time - models predict O_2 abundances a factor of ten larger than the observational upper limit. Another is the lack of consistency among models of the chem. and microphysics in different regions, esp. in the cloud layers, where the mixing ratios of many important trace species change by orders of magnitude within several vertical scale heights, and at the surface. A third is the mechanism(s) creating an inversion layer in SO_2 abundances in the mesosphere. This talk presents an overview of our current understanding and key unresolved issues