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A Water Vapor Measurement Amid a Largely Quiescent Environment on Europa
Wednesday, May 27, 2020 - 3:30pm PDT
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Previously detected local anomalies in Europa's atmosphere advanced the idea of possible water plumes on the Jovian moon – an exciting possibility our team wanted to investigate further. Through a global survey with the Keck Observatory, we were able to detect a direct (3.1-sigma) line emission from water at infrared wavelengths on one out of 17 observing dates in 2016 and 2017. The non-detections on the 16 other dates resulted in sensitive upper limits for water abundance at various longitudes, providing a reference to the rate of occurrence as well as the to the water abundance limits.
In 2016, we began an observing program aimed at characterizing the chemical composition of Europa's thin atmosphere—particularly water vapor—with the near-infrared spectrograph (NIRSPEC) at the 10-m Keck Observatory. The key advantage of observations at infrared wavelengths is the ability to measure H2O (not H and O), thereby providing a direct and independent assessment of water vapor in Europa's thin atmosphere.
The new results from the infrared survey suggest that outgassing occurs at lower levels than previously estimated, with only rare localized events of somewhat stronger plume activity. During this presentation, I will discuss our observational journey, put our observations in context, and share lessons learned.