Planetary and exoplanetary Astronomy Lunch Seminar (PALS) for 2021-09-27

Series: Planetary and exoplanetary Astronomy Lunch Seminar (PALS)
Date: Monday 27-Sep-2021
Time: 11:15-12:15
Location: PSC 1136(!) and via Zoom (link sent out to the PALS distribution list prior to the talk)
Speaker: Michael Zhang (Caltech)
Title: The Atmospheres of Sub-Neptunes: Photoevaporation, JWST, and more

The atmospheres of planets smaller than Neptune remain largely mysterious. A radius gap divides the larger mini Neptunes from the smaller super Earths; under the prevailing theory, photoevaporation in the planet's youth strips some mini Neptunes of their envelopes, turning them into super Earths. We report the first evidence for escaping primordial atmospheres from two young mini Neptunes, and run extensive 1D and 3D hydrodynamic models to explore the complex effects of stellar wind and metallicity upon the observed signals. The absorption is generally weaker than models predict, pointing to suppression mechanisms such as high atmospheric metallicity or magnetic fields.

In the second part of my talk, I focus on rocky planets. These include 55 Cnc e, where our non-detection of escaping helium to deep limits, and our 3D models, both suggest the planet cannot have a primordial atmosphere. They include GJ 367b, an ultra short period sub-Earth for which a JWST phase curve will reveal atmospheric or surface properties. I will describe the JWST programs targeting these planets, what we will learn from them, and how I plan to improve atmospheric modelling with JWST data.

For further information contact PALS coordinators Drs. Quanzhi Ye ( and Matej Malik (


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

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