Saturn ring rain: Model estimates of water influx into Saturn’s atmosphere

Moore, Luke; O’Donoghue, James; Müller‐Wodarg, I. C. F.; Galand, M.; Mendillo, M.

doi:10.1016/j.icarus.2014.08.041

Cited by 38 publications

(69 citation statements)

References 86 publications

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“…Drossart et al 1989;Baron et al 1991;Trafton et al 1993;Rego 2000;Stallard et al 2008;Miller et al 2010), not only allowing determination of H + 3 densities and temperatures, but also providing valuable constraints for ionospheric models (e.g. Moore et al 2015). However, H + 3 emissions have never been detected from an exoplanetary atmosphere, and the predicted emission levels are too low to be detected from planets orbiting stars of similar type and age to the Sun (Shkolnik et al 2006;Koskinen et al 2007).…”

Section: Introductionmentioning

confidence: 99%

EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

Chadney

Galand

Koskinen

et al. 2016

A&A

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The composition and structure of the upper atmospheres of extrasolar giant planets (EGPs) are affected by the high-energy spectrum of their host stars from soft X-rays to the extreme ultraviolet (EUV). This emission depends on the activity level of the star, which is primarily determined by its age. In this study, we focus upon EGPs orbiting K-and M-dwarf stars of different ages -Eridani, AD Leonis, AU Microscopii -and the Sun. X-ray and EUV (XUV) spectra for these stars are constructed using a coronal model. These spectra are used to drive both a thermospheric model and an ionospheric model, providing densities of neutral and ion species. Ionisation -as a result of stellar radiation deposition -is included through photo-ionisation and electron-impact processes. The former is calculated by solving the Lambert-Beer law, while the latter is calculated from a supra-thermal electron transport model. We find that EGP ionospheres at all orbital distances considered (0.1−1 AU) and around all stars selected are dominated by the long-lived H + ion. In addition, planets with upper atmospheres where H 2 is not substantially dissociated (at large orbital distances) have a layer in which H + 3 is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H + 3 undergo significant diurnal variations, with the maximum value being driven by the stellar X-ray flux. In contrast, densities of longer-lived H + show very little day/night variability and the magnitude is driven by the level of stellar EUV flux. The H + 3 peak in EGPs with upper atmospheres where H 2 is dissociated (orbiting close to their star) under strong stellar illumination is pushed to altitudes below the homopause, where this ion is likely to be destroyed through reactions with heavy species (e.g. hydrocarbons, water). The inclusion of secondary ionisation processes produces significantly enhanced ion and electron densities at altitudes below the main EUV ionisation peak, as compared to models that do not include electron-impact ionisation. We estimate infrared emissions from H + 3 , and while, in an H/H 2 /He atmosphere, these are larger from planets orbiting close to more active stars, they still appear too low to be detected with current observatories.

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Section: Introductionmentioning

confidence: 99%

EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

Chadney

Galand

Koskinen

et al. 2016

A&A

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“…The strong variations in TEC are matched by similar variations in NmS2, and they are driven primarily by the ring-derived water influxes estimated from model comparisons with the latitudinal variations of H 3 + emissions ( O' Donoghue et al, 2013;. Note that the Moore et al (2015) simulations were performed for comparisons with a specific day of H 3 + observations (17 April 2011), and therefore cannot be compared directly with the variations in electron density derived from the radio occultations summarized in Fig. 3 which were obtained over a wide range of seasonal and solar conditions.…”

Section: Sources Of Variability At Middle Latitudes: Intrusions Of Lomentioning

confidence: 65%

“…8 of Moore et al (2015) . Moore et al (2015) estimated that, based on ground-based observations of H 3 + ring rain signatures, the ring-derived water flux could vary by more than an order of magnitude over only a few degrees of latitude. The strong variations in TEC are matched by similar variations in NmS2, and they are driven primarily by the ring-derived water influxes estimated from model comparisons with the latitudinal variations of H 3 + emissions ( O' Donoghue et al, 2013;.…”

Section: Sources Of Variability At Middle Latitudes: Intrusions Of Lomentioning

confidence: 98%

“…[The mean value itself (6461 e − /cm 3 ) has an errorof-the mean of ∼15%, computed from σ / √ n, where n = number of observations.] From the model calculations of Moore et al (2015) , this NmS2 average electron density corresponds to a water flux of ∼4 × 10 6 cm −2 s −1 . Variability of ∼ 84% about the mean NmS2 could be explained by a range of water flux from roughly (2 -50) x 10 6 cm −2 s −1 .…”

Section: Source Of Variability At Low Latitudes: Models Of Changing Wmentioning

confidence: 98%

“…10 , which shows modeled TEC versus latitude based on the water fluxes derived in Fig. 8 of Moore et al (2015) . Moore et al (2015) estimated that, based on ground-based observations of H 3 + ring rain signatures, the ring-derived water flux could vary by more than an order of magnitude over only a few degrees of latitude.…”

Section: Sources Of Variability At Middle Latitudes: Intrusions Of Lomentioning

confidence: 99%

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Comparative ionospheres: Terrestrial and giant planets

Mendillo

Trovato

Moore

et al. 2018

Icarus

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a b s t r a c tThe study of planetary ionospheres within our solar system offers a variety of settings to probe mechanisms of photo-ionization, chemical loss, and plasma transport. Ionospheres are a minor component of upper atmospheres, and thus their mix of ions observed depends on the neutral gas composition of their parent atmospheres. The same solar irradiance (x-rays and extreme-ultra-violet vs. wavelength) impinges upon each of these atmospheres, with solar flux magnitudes changed only by the inverse square of distance from the Sun. If all planets had the same neutral atmosphere-with ionospheres governed by photochemical equilibrium (production = loss)-their peak electron densities would decrease as the inverse of distance from the Sun, and any changes in solar output would exhibit coherent effects throughout the solar system.Here we examine the outer planet with the most observations of its ionosphere (Saturn) and compare its patterns of electron density with those at Earth under the same-day solar conditions. We show that, while the average magnitudes of the major layers of molecular ions at Earth and Saturn are approximately in accord with distance effects, only minor correlations exist between solar effects and day-to-day electron densities. This is in marked contrast to the strong correlations found between the ionospheres of Earth and Mars. Moreover, the variability observed for Saturn's ionosphere (maximum electron density and total electron content) is much larger than found at Earth and Mars. With solar irradiance changes far too small to cause such effects, we use model results to explore the roles of other agents. We find that water sources from Enceladus at low latitudes, and 'ring rain' at middle latitudes, contribute substantially to variability via water ion chemistry. Thermospheric winds and electrodynamics generated at auroral latitudes are suggested causes of high latitude ionospheric variability, but remain inconclusive due to the lack of relevant observations.

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Redetection of the Ionospheric Signature of Saturn's “Ring Rain”

O’Donoghue

Moore

Connerney

et al. 2017

Geophysical Research Letters

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In April 2011 Saturn's midlatitude ionospheric normalH3+ emissions were detected, exhibiting anomalous (nonsolar) normalH3+ latitudinal variations consistent with the transport of water from specific locations in Saturn's rings, known as “ring rain”. These products, transported to the planet along the magnetic field, may help to explain the unusual pattern of peaks and troughs in electron densities discovered in Saturn's ionosphere by spacecraft flybys. In the present study, we analyzed normalH3+ emissions recorded on 23 April 2013, showing for the first time since the original detection that Saturn's midlatitude normalH3+ emissions are indeed heavily modified. Although the 2013 emissions are dimmer by almost a factor of 3.7, the latitudinal contrast is greater and uncertainties are lower. Increased normalH3+ intensities were found near planetocentric latitudes of 43°, 51°, and 63°, previously identified with sources at the inner edge of the B ring, A ring, and the orbit of Enceladus and associated E ring.

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Saturn ring rain: Model estimates of water influx into Saturn’s atmosphere

Abstract: 9Recently H 3 + was detected at Saturn's low-and mid-latitudes for the first time (O'Donoghue et 10

Cited by 38 publications

References 86 publications

EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

Comparative ionospheres: Terrestrial and giant planets

Redetection of the Ionospheric Signature of Saturn's “Ring Rain”

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