Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1408.1746

Saturn's upper atmosphere during the Voyager era: Reanalysis and modeling of the UVS occultations

Ronald J. Vervack Jr.·Julianne I. Moses
View original source ↗Read source document ↗Export metadata ↓

Abstract

The Voyager 1 and 2 Ultraviolet Spectrometer (UVS) solar and stellar occultation dataset represents one of the primary, pre-Cassini sources of information that we have on the neutral upper atmosphere of Saturn. Despite its importance, however, the full set of occultations has never received a consistent, nor complete, analysis, and the results derived from the initial analyses over thirty years ago left questions about the temperature and density profiles unanswered. We have reanalyzed all six of the UVS occultations (three solar and three stellar) to provide an up-to-date, pre-Cassini view of Saturn's upper atmosphere. From the Voyager UVS data, we have determined vertical profiles for H2, H, CH4, C2H2 , C2H4, and C2H6, as well as temperature. Our analysis also provides explanations for the two different thermospheric temperatures derived in earlier analyses (400-450 K versus 800 K) and for the unusual shape of the total density profile noted by Hubbard et al. (1997). Aside from inverting the occultation data to retrieve densities and temperatures, we have investigated the atmospheric structure through a series of photochemical models to infer the strength of atmospheric mixing and other physical and chemical properties of Saturn's mesopause region during the Voyager flybys. We find that the data exhibit considerable variability in the vertical profiles for methane, suggesting variations in vertical winds or the eddy diffusion coefficient as a function of latitude and/or time in Saturn's upper atmosphere. The results of our reanalysis will provide a useful baseline for interpreting new data from Cassini, particularly in the context of change over the past three decades.

Explore related subjects

astro-ph.EP

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Ronald J. Vervack Jr., Julianne I. Moses. 2014-08-08. Saturn's upper atmosphere during the Voyager era: Reanalysis and modeling of the UVS occultations. https://doi.org/10.1016/j.icarus.2015.06.007

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Bridging magnetothermal winds and photoevaporation to model discs dispersal

Protoplanetary disc dispersal is driven by two processes usually modelled separately: photoevaporative and magnetohydrodynamic (MHD) disc winds. Global simulations indicate that in the inner disc these are not distinct outflows but a single magnetothermal wind. We assemble a closed-form, two-phase model that respects it. A single-field-line wind, whose base is fixed by the irradiated temperature and penetration column, supplies the launch and feeds a secular evolution, with photoevaporation convolved on as a sink. The flux closure $B_z\proptoΣ^q$ is self-limiting: for $q\le1/2$ depletion alone cannot demagnetise the disc, so dispersal requires independent flux loss, parameterised by the magnetic Reynolds number $\mathcal{R}_m$. Integrating the coupled system yields two regimes. Efficient flux loss ($\mathcal{R}_m\lesssim1$) lets the magnetisation front recede by over an order of magnitude and opens a photoevaporative gap. Flux retention ($\mathcal{R}_m\gg1$) drives the front outward, sustains accretion, and defers dispersal by $\approx2.7$~Myr. Deriving the base from stellar irradiation instead of prescribing it, we find that the cold-launch approximation is valid during the early stages of disc evolution: anchoring the base at plasma equipartition ($β_{\rm base} \sim 1$) confines irradiation's influence on the magnetic lever arm to the magnetothermal annulus, decoupling the peak accretion rate from the incident flux. Both regimes clear the disc inside-out, through either a photoevaporatively amplified cavity wall or an expanding magnetothermal front.

astro-ph.EP↗
arXiv2026

Faithful Neural Embeddings for 3D Exoplanet Climate Modeling

With the rapid advancement of telescopes like JWST and Ariel, there is an urgent need for efficient 3D climate models to interpret observations of exoplanet atmospheres. Traditional 3D general circulation models (GCMs) are computationally intensive, prompting the development of machine learning (ML) emulators to accelerate simulations. Recent work, such as that by Plaschzug et al. 2026 \cite{plaschzug2026accelerating}, uses a dense neural network (DNN) to predict local gas temperatures and winds from input parameters, including local gas pressure, spatial coordinates (longitude and latitude), and global temperature. However, this model relies on predicting individual temperature values (points) at specific grid points, which can be limited by the resolution and constraints of the training grid. In this work, we investigate a couple of alternative frameworks based on latent-space representations of local gas temperature ($\text{T}_{\text{gas}}$) to obtain a faithful, low-dimensional representation of these profiles. This represents the first step toward developing a latent space regression model, offering a structurally cohesive alternative to the existing point-wise prediction method \cite{plaschzug2026accelerating}. By capturing the optimal embedding space of atmospheric data, our proposed framework can produce simulated profiles while maintaining computational efficiency, making it suitable for large-scale exoplanet ensemble studies.

astro-ph.EP↗
arXiv2026

Some challenges for the long-term survival of Naiad, Neptune's innermost moon

The Naiad-Thalassa 73:69 mean-motion resonance implies these moons have co-existed for $\gtrsim$1 Gyr, raising the question of how they survived to the present day. We examine three challenges to Naiad's long-term survival: tidal disruption, heliocentric bombardment, and runaway collisional erosion by planetocentric debris. We constrain Naiad's internal strength requirements from its nominal density and shape, compute present-day impact rates on Neptune's inner moons from heliocentric bombardment, and use $N$-body simulations to model the fate of ejecta produced by non-disruptive impacts. First, Naiad's nominal density of ${\sim}0.8\text{ g cm}^{-3}$ and elongated shape suggest it cannot be held together by self-gravity alone, implying a cohesive strength of $\gtrsim10$ kPa to avoid tidal disruption, although this constraint is relaxed if Naiad has a higher density of ${\gtrsim}1.3\text{ g cm}^{-3}$. Second, we show that Naiad may have been disrupted in the last 1 Gyr by heliocentric bombardment, although this depends sensitively on the size-frequency distribution of Kuiper Belt objects at small sizes and on Naiad's catastrophic disruption threshold, both of which are poorly constrained. Third, and most notably, we find that even small, non-disruptive impacts can trigger runaway collisional erosion by planetocentric debris on extremely short timescales. Avoiding this ``sesquinary catastrophe'' requires that Naiad has a collisional strength of at least several MPa, which is difficult to reconcile with being a reaccumulated ``rubble pile'', leftover from the capture of Triton and the subsequent cataclysm of Neptune's primordial satellite system. Together, these results suggest that Naiad may be a physically unusual object among small ring-moons -- possibly a largely coherent, monolithic fragment -- and that our understanding of Neptune's inner satellite system leaves much to be explained.

astro-ph.EP↗