Constraining Time Variations in Enceladus’ Water-Vapor Plume With Near-Infrared Spectra from Cassini-VIMS

By Keith Cowing
Status Report
May 14, 2024
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Constraining Time Variations in Enceladus’ Water-Vapor Plume With Near-Infrared Spectra from Cassini-VIMS
Left: Map of the plume’s brightness at 2.70 µm derived from an average of five VIMS cubes (V1511798376, V1511800181, V1511800741, V1511801493, and V1511802247). Note that this brightness is mostly due to reflected sunlight from Enceladus’ lit limb and the plume particles. The image is re-projected on a grid with 19 kilometers per pixel and oriented so that the plume points downward. Right: Map of the water-vapor column density derived from the same averaged image. Column densities were calculated using the average residual values and Equation 1. Note that regions of high column density are visible outside the region where the plume particles are bright, which provides evidence that this signal traces a different plume component. The red circles outline Enceladus and the red rectangles show the pixels used for the spectral analysis — astro-ph.EP

Water vapor produces a series of diagnostic emission lines in the near infrared between 2.60 and 2.75 microns. The Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft detected this emission signal from Enceladus’ plume, and so VIMS observations provide information about the variability of the plume’s water vapor content.

Using a data set of 249 spectral cubes with relatively high signal-to-noise ratios, we confirmed the strength of this water-vapor emission feature corresponds to a line-of-sight column density of order 10^20 molecules/m^2, which is consistent with previous measurements from Cassini’s Ultraviolet Imaging Spectrograph (UVIS).

Comparing observations made at different times indicates that the water-vapor flux is unlikely to vary systematically with Enceladus’ orbital phase, unlike the particle flux, which does vary with orbital phase. However, variations in the column density on longer and shorter timescales cannot be ruled out and merit further investigation.

Katie Denny, Matthew Hedman, Dominique Bockelée-Morvan, Gianrico Filacchione, Fabrizio Capaccioni

Comments: 16 pages, 11 figures, 1 supplemental table (ascii format)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.07428 [astro-ph.EP] (or arXiv:2405.07428v1 [astro-ph.EP] for this version)
Submission history
From: Katie Denny
[v1] Mon, 13 May 2024 02:02:16 UTC (7,588 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻