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JGR Planets - 2022 - King - Global Modeling of Ganymede s Surface Composition Near‐IR Mapping From VLT SPHERE.pdf (3.92 MB)

Global Modeling of Ganymede's Surface Composition: Near‐IR Mapping From VLT/SPHERE

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journal contribution
posted on 2024-01-23, 11:17 authored by Oliver King, Leigh N Fletcher

We present maps of Ganymede's surface composition with almost complete longitude coverage, acquired using high spatial resolution near-infrared (0.95–1.65 μm) observations from the ground-based VLT/SPHERE instrument. Observed reflectance spectra were modeled using a Markov Chain Monte Carlo method to estimate abundances and associated uncertainties of water ices, acids, salts and a spectrally flat darkening agent. Results confirm Ganymede's surface is dominated by water ice in young bright terrain (impact craters, sulci), and low-albedo spectrally flat material in older dark terrain (e.g., Galileo Regio). Ice grain size has strong latitudinal and longitudinal gradients, with larger grains at the equator and on the trailing hemisphere. These trends are consistent with the effects of the latitudinal thermal gradient and global variations in radiation driven sputtering. Sulfuric acid has a low abundance and appears potentially spatially correlated with plasma bombardment, where Ganymede's poles are exposed to the external Jovian magnetic field. Best-estimate abundances suggest a mixture of salts could be present, although their low abundances, spectral degeneracies and associated uncertainties mean individual salt species cannot be detected with confidence. If present, sodium magnesium sulfate and magnesium chlorate appear tentatively correlated with exogenic plasma bombardment, while magnesium chloride and sulfate appear tentatively correlated with younger terrain, implying a possible endogenic origin. MCMC modeling was also performed on Galileo/NIMS data, showing comparable distributions. The high spatial resolution of SPHERE allows the precise mapping of small scale (<150 km) surface features, which could be used along with higher spectral resolution observations to jointly confirm the presence and distribution of potential species.

Funding

Royal Society

University of Leicester

European Union’s Horizon 2020. Grant Number: 723890

History

Author affiliation

School of Physics & Astronomy, University of Leicester

Version

  • VoR (Version of Record)

Published in

Journal of Geophysical Research: Planets

Volume

127

Issue

12

Publisher

American Geophysical Union (AGU)

issn

2169-9097

eissn

2169-9100

Copyright date

2022

Available date

2024-01-23

Language

en

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