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DIX Planetary Science Seminar

Tuesday, April 27, 2021
4:00pm to 5:00pm
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The tidal excitation of Jupiter's dilute core & Photochemistry, Aerosols, and Evolution of Planetary Atmospheres
Ben Idini, Graduate Student, Planetary Science, California Institute of Technology,
Danica Adams, Graduate Student, Planetary Science, California Institue of Technology,

The tidal excitation of Jupiter's dilute core

NASA's Juno mission recently proposed that Jupiter hosts a dilute core with a compositional gradient that could be present as far out as ~0.6RJ, contrary to the traditional view of a compact core. Here we use simple models to evaluate the response of Jupiter's dilute core to tidal excitation. We model Jupiter's interior as a mixture of H-He fluid and heavy elements. The H-He fluid follows an n=1 polytrope, whereas heavy elements follow an empirical equation of state for 'rocky' heavy elements at high pressure. We previously determined a dynamical effect on k2 (the l=m=2 Love number) equal to -4% in the case of Io's tidal excitation of a homogeneous, adiabatic Jupiter model. Our results reported here suggest that a dilute core introduces an additional non-resonant effect close to +2% for a compositional gradient present at ~0.6RJ, leading to a -2% overall fractional correction. Our prediction neglects the dynamical contribution from g-modes trapped in the dilute core, excluding near-resonant effects from our results. The most recent Juno observation (perijove 17) agrees with our results but indicates a k2 uncertainty of 3% (3s), large enough to prevent us from discriminating among competing dilute core models. The uncertainty in the k2 Juno observation is expected to diminish by an order of magnitude at the end of Juno's extended mission (mid 2025), allowing us to test our prediction about the existence or extension of Jupiter's dilute core. Our prediction can provide the first estimate of the static stability in the proposed dilute core, a property capable of stabilizing large scale overturning convection and alter Jupiter's mixing rates and its capability to transport deeply seated heat out into the photosphere.

Photochemistry, Aerosols, and Evolution of Planetary Atmospheres

The "habitable zone" is a general definition commonly used to categorize planetary habitability. While useful in a statistical approach to exoplanet categorization, this definition does not guarantee habitability, as it ignores important atmospheric feedback and weathering cycles, and it cannot inform the prebiotic chemistry critical to the origins of life. A planet being ‘just right' for habitability requires a delicate balance between its atmospheric chemistry, radiation environment, and surface processes. Prebiotic chemistry could begin in the atmosphere, for example via nitrogen fixation or photolysis of methane yielding complex hydrocarbons, and there are abundant worlds (both in and out of the Solar System) that have or have had chemistry that is conducive to the origins of life. Mars is thought to have been warm and wet in its early history, and N- and S- bearing species may have implications for prebiotic synthesis. Early Earth is also known to host interesting nitrogen chemistry important to early life, and Titan has complex hydrocarbon and nitrile chemistry suitable for the production of amino acids. Importantly, planets are not static; they change and evolve through time, and exoplanets are an excellent opportunity to examine planets of different stages in evolution. Studying observable (exo)planets (habitable or not) will improve understanding of planet types for which we have no examples in the solar system (eg, super-Earths, sub-Neptunes, and hot Jupiters) and improve understanding of critical physical and chemical processes (thermochemistry, photochemistry, aerosol microphysics, atmospheric evolution) which will be applicable to interpret future observations of other habitable worlds. This talk will present highlights of my recent work exploring these worlds.

For more information, please contact Aida Behmard by email at abehmard@caltech.edu.