ExoExplorer Science Series: Munazza Alam (Carnegie EPL) & Matt Clement (Carnegie EPL)

The ExoExplorer Science Series presents talks by cohort members Munazza Alam (Carnegie EPL) & Matt Clement (Carnegie EPL) on January 21, 2022, from 11 AM - 12 PM Pacific / 2 PM - 3 PM Eastern. Connection information is below.

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Speaker: Munazza Alam (Carnegie EPL)

Title: The First Near-Infrared Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System

Abstract: We present a near-infrared transmission spectrum of the long period (P=542 days), temperate (T_eq=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope (HST). With a measured mass of ~12 M_earth and a radius of ~9R_earth, HIP 41378 f has an extremely low bulk density (0.09 g/cm^3). We measure the transit depth with a typical precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.

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Speaker: Matt Clement (Carnegie EPL)

Title: Solar and extra-solar terrestrial planet formation: The bleak prospects for habitability around the smallest stars

Abstract: While the solar system's geologic and observational accessibility makes it an unparalleled laboratory in which to study planet formation, exoplanet science has revealed a diverse continuum of evolutionary pathways followed by other systems. Emboldened by these advancements, recent investigations have reevaluated and modernized standard models of planet formation originally based on classic solar system studies. Building from this solar system analogy, contemporary work on exoplanet formation has found that the generic terrestrial planet growth regime is highly sensitive to several key processes. Namely, these include the presence of giant planets, the radial pebble flux, and the formation location of planetary cores. Further invigorating this field, pioneering exoplanet survey missions like Kepler and TESS have spurred a prolific output of multifaceted investigations into the formation of newly detected worlds. Through these advancements, a paradigm shift has occurred in exoplanet science, wherein low-mass stars are increasingly viewed as a foundational pillar of the search for potentially habitable worlds in the solar neighborhood. However, the processes that led to the formation of this rapidly accumulating sample of systems are still poorly understood. Moreover, it is unclear whether tenuous primordial atmospheres around these Earth-analogs could have survived the intense epoch of heightened stellar activity that is typical for low-mass stars. I will summarize our understanding of rocky planet formation and volatile delivery in the solar system, and how these ideas extend to the low-mass regime. I will then present results from new simulations of in-situ planet formation across the M-dwarf mass spectrum. From these calculations, we derive leftover debris populations of small bodies that might source delayed volatile delivery. We then follow the evolution of this debris with high-resolution models of real systems of habitable zone planets around low-mass stars such as TRAPPIST-1.

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