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Dix Planetary Science Seminar

Tuesday, February 11, 2020
4:00pm to 5:00pm
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South Mudd 365
"Overturning Ocean Circulations in Ocean Worlds" and "Observations of Exoplanetary Mass Loss with Ultra-Narrowband Helium Photometry"
Shreyas Vissapragada & Ana Lobo, Graduate Students, Planetary Science, Caltech,

"Overturning Ocean Circulations in Ocean Worlds"

Ana Lobo

Graduate Student – Planetary Sciences


Abstract: Liquid water oceans within our solar system provide intriguing laboratories for the coupled interaction between physical, chemical and biological processes needed to support life. Both the ocean's stratification and its ability to distribute heat and tracers along and across density surfaces is critical for understanding the relationship between a global ocean and the planetary energy budget, including the dissipation of tidal heating and the transport of geothermal heat from the interior to the ice surface. Similar to Earth's ocean, the circulation dynamics of oceans such as those on Enceladus, Europa, and Titan and the subsequent heat and salt distributions are likely to be controlled by processes occurring at the ocean boundaries. Variations in the ice shell thicknesses of these bodies, which were recently inferred from Cassini observations for Enceladus and Titan, are valuable diagnostics for distinguishing circulation properties of various ocean worlds. Here, we focus on horizontal convection driven by equator-to-pole buoyancy differences that could be caused by latitudinal ice transport at the ocean surface, as well as the impact of a freshwater layer formed by ice melting, and the consequences of an imposed surface slope due to varying ice thickness.

"Observations of Exoplanetary Mass Loss with Ultra-Narrowband Helium Photometry"

Shreyas Vissapragada

Graduate Student – Planetary Sciences


Abstract: Infrared observations of metastable 2$^3$S helium absorption with ground- and space-based spectroscopy are rapidly maturing as unique probes of exoplanet atmospheres. The transit depth in the triplet feature (with vacuum wavelengths near 1083.3 nm) can be used to constrain the temperature and mass loss rate of an exoplanet's upper atmosphere. Here, we present a new photometric technique to measure metastable 2$^3$S helium absorption using an ultra-narrowband filter (full-width at half-maximum of 0.635 nm) coupled to a beam-shaping diffuser installed in the Wide-field Infrared Camera (WIRC) on the 200-inch Hale Telescope at Palomar Observatory. We use telluric OH lines and a helium arc lamp to characterize refractive effects through the filter and to confirm our understanding of the filter transmission profile. We show observations of WASP-69b and WASP-52b that benchmark this experimental setup and demonstrate that ultra-narrowband photometry can reliably quantify absorption in the metastable helium feature, allowing for constraints on exoplanetary mass loss.

For more information, please contact Shreyas Vissapragada by email at [email protected].