Planetary Lunch Seminar – Prajwal Niraula (MIT)

The Grand Opacity Challenge: Opacity-driven Biases in Exoplanet Atmospheric Characterization.

Abstract: Remote sensing enables the study of worlds beyond Earth’s neighborhood by leveraging the dependence of light-matter interaction to local conditions to gain insights into, e.g., local composition. The remote sensing of exoplanet atmospheres is currently limited by instruments. With the upcoming generation of observatories, the instrumental contribution to the overall uncertainty budget will decrease. Here, we report on the share of opacity models in this future budget. We perform a sensitivity analysis using red{nine} different opacity cross-sections representative of standard assumptions and find that despite differences in the cross-sections, most of the retrievals produce harmonious fits owing to compensations in the form of $>$5$sigma$ biases on the derived atmospheric parameters. These biases reveal an accuracy wall at $sim$0.5-1.0 dex (i.e., 3 to 10$times$), which is an order of magnitude above the precision targeted by textit{JWST} Cycle 1 programs and needed for, e.g., red{meaningful C/O-ratio constraints and biosignatures identification}. We suggest a two-tier approach to alleviate this problem involving a new retrieval procedure and guided improvements in opacity data, their standardization and optimal dissemination.

About this Series: The MIT Planetary Lunch Seminar [PLS] is a weekly seminar series organized within the EAPS department. Colloquia topics span the range of research interests of the department’s planetary sciences research program. The seminars take place on Tuesdays from 12:30–1:30 pm, unless otherwise noted (term-time only). Speakers include members of the MIT community and visitors. Talks are intended to appeal to graduate students, postdocs, research scientists, and faculty with a background in planetary science. Contact: planetary-org@mit.edu.