March 17, 2023

The ExoExplorer Science Series presents talks by cohort members Anjali Piette (Carnegie EPL) & Pa Chia Thao (U of North Carolina Chapel Hill) on March 17, 2023, from 11 AM - 12 PM Pacific / 2 PM - 3 PM Eastern. Connection information is below.

Speaker: Anjali Piette (Carnegie EPL)

Title: The Observability of Low-Density Lava World Atmospheres: A Window into Super-Earth Interior Compositions

Abstract: The super-Earth population spans a wide range of bulk densities, indicating a diversity in interior conditions beyond that seen in the solar system. In particular, a growing population of low-density super-Earths may be explained by volatile-rich interior compositions. Among these, lava worlds, with dayside temperatures high enough to evaporate their surfaces, provide a unique opportunity to probe the diverse surface and interior compositions of super-Earths. In this talk, I will discuss the atmospheric observability of low-density lava worlds, whose bulk densities are consistent with volatile-rich interior compositions. Using self-consistent 1D atmospheric models, I explore the atmospheric structures and thermal emission spectra of these planets across a range of mixed rock vapor/volatile compositions. Spectral features due to both volatile and rock vapor species are present in the infrared thermal emission spectra, though the strength of such features - and whether they appear as emission or absorption features - depends on the dayside temperature and atmospheric composition. In order to assess the observability of such features with JWST, I simulate JWST thermal emission observations and perform synthetic atmospheric retrievals for three promising targets. Detecting volatiles in the atmospheres of these evaporating exoplanets would provide new evidence that volatile-rich interiors exist among the super-Earth population.

Speaker: Pa Chia Thao (U of North Carolina Chapel Hill)

Title: Hazy with a Chance of Star Spots: Constraining the Atmosphere of the Young Planet, K2-33b

Abstract: Studying the properties of planets across a wide range of ages will help provide insights into the processes that shape their formation and evolution. While all-sky surveys have discovered dozens of young planets (<1 Gyr), their atmospheres remain largely unknown. In this study, we explore the transmission spectrum of K2-33b, the youngest (10 Myr), transiting exoplanet discovered. Using multi-wavelength data obtained from K2, MEarth, HST, and Spitzer, we found that the optical transit depths were nearly 2 times deeper than the near-infrared depths. This difference holds across multiple data sets taken over two years, ruling out issues of data analysis and unconstrained systematics. While surface inhomogeneities on the young star could have contributed to the observed difference, the observed stellar spectra ruled out the required spot coverage fractions. Instead, we found that a tholin haze with carbon monoxide as the dominant carbon carrier provided a better fit to the transmission spectrum. A companion study found that a circumplanetary dust ring can also explain the transit depth difference. Further observations are needed to separate the two scenarios, confirm the presence of CO, and map out the role of spots on the transmission spectrum.

Meeting link:
Meeting number:
2763 643 6746