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Dix Planetary Science Seminar

Tuesday, June 2, 2020
4:00pm to 5:00pm
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Online Event
Benjamin Idini, Graduate Student, Geophysics, Caltech,
Yayaati Chachan, Graduate Student, Planetary Science,
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Yayaati Chachan

Title: Hazy Spectra, Mass Loss Histories, and Formation of 'Super-Puffs'

Abstract: Extremely low density planets (‘super-puffs') are a small but intriguing subset of the transiting planet population. With masses in the super-Earth range (1—10 M$_{\oplus}$) and radii akin to those of giant planets (>4 R$_{\oplus}$), their large (10s of % by mass) envelopes may have been accreted beyond the water snow line and many appear to be susceptible to catastrophic mass loss. Both the presence of water and the importance of mass loss can be explored using transmission spectroscopy. However, despite being promising candidates for transmission spectroscopy, they seem to possess featureless near-infrared spectra. Here, we present newHST WFC3 spectroscopy and updated Kepler transit depth measurements for the super-puff Kepler-79d. Although we do not detect any molecular absorption features in the 1.1-1.7 $\mu$m WFC3 bandpass, the combination of Kepler and WFC3 data reveals the presence of a scattering signature. We use a microphysical haze model to show that photochemical hazes offer an attractive explanation for the observed properties of super-puffs like Kepler-79d, as they simultaneously render the near-infrared spectrum featureless and reduce the inferred envelope mass loss rate by moving the measured radius (optical depth unity surface during transit) to lower pressures. We revisit the broader question of mass loss rates for super-puffs and find that the age estimates and mass loss rates for the majority of super-puffs can be reconciled if hazes move the photosphere from the typically assumed pressure of ~10 mbar to ~10 $\mu$bar. Finally, we use dust evolution models to show that the protoplanetary disk conditions required for the acquisition of large envelopes by super-puffs may be realized beyond the water snow line. We conclude by discussing some ongoing work on the location dependence of envelope accretion by planetary cores and its consequences for planet formation.

Benjamin Idini

Dynamical tides in the Jovian System as revealed by Juno

Abstract: Since 2016, the Juno orbiter has been collecting measurements of Jupiter's gravity field with an exquisite accuracy not seen before in the exploration of any other giant planet. Preliminary analysis of doppler shifts from Juno's trajectory over 17 perijove passes suggest the presence of a non-hydrostatic component in the amplitude of the tides that the Galilean moons raise on Jupiter. In this presentation I will propose dynamical tides as a candidate to reconcile Juno measurements of Jupiter's gravitational field with tidal theory. Part of our analysis suggests that Europa and Io may be at resonance with inertial modes in Jupiter's interior. Furthermore, I will discuss our progress on using the measured non-hydrostatic component of tides to infer the extension of Jupiter's potentially diluted core.

For more information, please contact Shreyas Vissapragada by email at svissapr@caltech.edu.