Ganymede's UV Reflectance From Juno‐UVS Data

Molyneux, Philippa M.; Greathouse, Thomas; Gladstone, G. R.; Versteeg, M. H.; Hue, V.; Kammer, Joshua A.; Davis, Michael W.; Bolton, S. J.; Giles, Rohini; Connerney, J. E. P.; Gérard, Jean‐Claude; Grodent, Denis

doi:10.1029/2022gl099532

Cited by 7 publications

(4 citation statements)

References 59 publications

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“…However, differences in the two studies such as geometry, sunlit versus nightside observations, a focus in this study on specifically the auroral regions and not disk averages, as well as extremely short integrations times by UVS (17 ms per spin) compared to almost half hour integrations from HST make comparing the results in the two studies complicated. For more detail about the dayside reflected emissions see Molyneux et al (2018Molyneux et al ( , 2022. Detailed models (e.g., Duling et al, 2014;Jia et al, 2009;Saur et al, 2015) along with the results of Eviatar et al (2001) suggest that the polar-most boundary of the auroral emissions is the position of the last closed field lines of Ganymede's magnetosphere.…”

Section: Pj34 Encountermentioning

confidence: 99%

UVS Observations of Ganymede's Aurora During Juno Orbits 34 and 35

Greathouse

Gladstone

Molyneux

et al. 2022

Geophysical Research Letters

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On 7 June 2021, Juno‐UVS mapped Ganymede's auroral emissions near a closest approach altitude of 1,046 km. The high spatial resolution map exhibits bright, 200–1,000 R, oxygen emissions organized into northern and southern auroral ovals. Though the map has incomplete global coverage, UVS observed longitudinal structure similar to that described by McGrath et al. (2013), https://doi.org/10.1002/jgra.50122 and latitudinal and vertical structure never before resolved. The mapped auroral emissions (a) display an intense narrow auroral curtain with a sharp poleward boundary, (b) have a more slowly decreasing equatorial edge on the leading hemisphere, (c) appear to originate near the surface with a vertical extent of 25–50 km, and (d) are slightly brighter in the north than the south. Additionally, we present UVS observations from the more distant Juno Ganymede flyby on 20 July 2021. We describe the observations, compare them to previous Hubble Space Telescope observations and current model predictions of the open‐closed‐field line‐boundary.

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Section: Pj34 Encountermentioning

confidence: 99%

UVS Observations of Ganymede's Aurora During Juno Orbits 34 and 35

Greathouse

Gladstone

Molyneux

et al. 2022

Geophysical Research Letters

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“…Visible images from the SRU and JunoCam reveal detail at higher resolution, in stereo, and with better quality in the imaged region than the best of the existing Voyager and Galileo coverage, enabling improvements to the geologic and topographic maps (Becker et al., 2022 ; Ravine et al., 2022 ). Albedo mapped at ultraviolet wavelengths shows latitudinal trends in composition and ice grain size (Molyneux et al., 2022 ). Sputtering rates to evaluate energetic particle weathering of Ganymede's surface have been computed (Paranicas et al., 2022 ).…”

Section: Science Results Summarymentioning

confidence: 99%

Juno's Close Encounter With Ganymede—An Overview

Hansen

Bolton

Sulaiman

et al. 2022

Geophysical Research Letters

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Jupiter's moon Ganymede is the largest moon in the solar system and the only moon with its own intrinsic, permanent magnetic field that extends far beyond its surface to form a magnetosphere (Gurnett et al., 1996;Kivelson et al., 1996Kivelson et al., , 2002. The first missions to investigate Ganymede in detail were the Voyager flybys of Jupiter in 1979, and the Galileo mission, which orbited Jupiter from 1995 to 2003 and executed a series of six close Ganymede flybys (summarized by Volwerk et al., 2022). Key findings of these missions, combined with Earth-based observations from facilities such as Hubble and ALMA, are as follows.Ganymede has a fully differentiated interior including a metallic core (Anderson et al., 1996; Hussmann et al., 2022). A subsurface liquid salt-water ocean forms a global layer, the top of which can be no more than 330 km below the icy surface (Kivelson et al., 1999;Saur et al., 2015Saur et al., , 2018. Ganymede is slightly larger and denser than, and forms a class with, the two other large solar system moons Callisto and Saturn's Titan. However, Ganymede's complex geologic history, which includes tectonic and/or volcanic production of grooved terrain well after the moon's formation, cutting through ancient heavily cratered terrain, shows a very different formation and evolution history than the other large moons (Schenk et al., 2022).Ganymede's neutral molecular oxygen exosphere (Hall et al., 1998), sourced from sputtering, radiolysis, and sublimation of surface ice, is ionized by photo-ionization and electron impact on open field lines. O, H, and H 2 O have also been detected (

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“…In addition to the aforementioned satellites, recent measurements using the Jovian Infrared Auroral Mapper (JIRAM) on NASAʼs Juno spacecraft show evidence for a spectral feature at 2.22 μm on Ganymede, which has been postulated to be due to one of several different salts, including + NH 4 -bearing salts (Tosi et al 2024). Ganymede provides an exciting test for the thermally driven chemistry demonstrated here not only because both NH 3 (Molyneux et al 2022) and O 3 (Noll et al 1996;Hendrix et al 1999) have been tentatively detected on the surface, in addition to the O 3 precursor O 2 (Spencer et al 1995;Trumbo et al 2021), but also because the surface temperatures are considerably warmer on Ganymede (85-145 K; Hanel et al (1979)) than on the Uranian and Plutonian satellites. While Tosi et al (2024) ruled out -NO 3 based on the absence of a strong feature at wavelengths longer than 2.5 μm, the NO -3specific NH 4 NO 3 features appear outside of the wavelength range probed by JIRAM (6.5-7.5 μm).…”

Section: Astrophysical Implicationsmentioning

confidence: 88%

Thermal Oxidation Reaction between NH₃ and O₃: Low-temperature Formation of an NH4+ -bearing Salt

Tribbett,

Loeffler

2024

Planet. Sci. J.

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NH3 has long been predicted to be an important component of outer solar system bodies, yet detection of this compound suggests a low abundance or absence on many objects where it would be expected. Here, we demonstrate that a thermally driven oxidation reaction between ammonia (NH3) and ozone (O3) in a H2O + NH3 + O3 mixture may contribute to the low abundance of NH3 on some of these objects, as this reaction efficiently occurs at temperatures as low as 70 K. We determined the overall activation energy for this reaction to be 17 ± 2 kJ mol−1, which is consistent with other chemical systems that react at cryogenic temperatures. The loss of these two compounds coincides with the formation of NH 4 + and NO 3 − at low temperatures, both of which are observable with infrared spectroscopy. Warming our H2O + NH3 + O3 mixtures through sublimation, we find a number of higher-temperature phases, such as ammonia hemihydrate, nitric acid, and ammonium nitrate (NH4NO3). The most stable of these is NH4NO3, which remains on the substrate until temperatures near 270 K. The salt product within this sample contains near-infrared spectral features between 2.0 and 2.22 μm, which is a spectral region of interest for several outer solar system objects, including the Uranian satellites Miranda, Ariel and Umbriel, and Pluto's satellite Charon.

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Ganymede's UV Reflectance From Juno‐UVS Data

Cited by 7 publications

References 59 publications

UVS Observations of Ganymede's Aurora During Juno Orbits 34 and 35

UVS Observations of Ganymede's Aurora During Juno Orbits 34 and 35

Juno's Close Encounter With Ganymede—An Overview

Thermal Oxidation Reaction between NH₃ and O₃: Low-temperature Formation of an NH4+ -bearing Salt

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Ganymede's UV Reflectance From Juno‐UVS Data

Cited by 7 publications

References 59 publications

UVS Observations of Ganymede's Aurora During Juno Orbits 34 and 35

UVS Observations of Ganymede's Aurora During Juno Orbits 34 and 35

Juno's Close Encounter With Ganymede—An Overview

Thermal Oxidation Reaction between NH3 and O3: Low-temperature Formation of an NH4+ -bearing Salt

Contact Info

Product

Resources

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Thermal Oxidation Reaction between NH₃ and O₃: Low-temperature Formation of an NH4+ -bearing Salt