Remo Burn (MPIA)

Owing to observational advances, exoplanets are no longer treated as simple point masses in planet formation theory - their masses, radii, and thus densities are now measurable. Combined with atmospheric composition data, the characterization of exoplanets has revealed distinct populations of exoplanets, ranging from rocky super Earths to gaseous giant planets. However, the nature of the intermediate-sized sub-Neptunes remains mysterious.

In this talk, I will review why formation models predict the migration of sub-Neptunes from cold regions in the disk, implying a water-rich (or generally volatile-rich) composition. The final planetary mass and radius is only determined after thermodynamic and photoevaporative evolution over Gyr timescales. I will show how the partitioning and phase of the volatile species affects the sub-Neptune population and their transition to become a rocky planet. While a treatment of water as steam mixed with H/He is relatively successful in reproducing the observed exoplanet demographics, the expected sequestration of volatiles to the planetary interior is so far rarely explored in the field and can have a large impact on the outcome. Moreover, future works need to include a realistic chemical makeup of the planets.

Kazumasa Ohno (NAOJ)

Michael L. Wong & Anirudh Prabhu (Carnegie Earth & Planets Laboratory)

Humanity is embarking on a potential golden age of astrobiology, with numerous current and future space missions being tasked with the explicit goal of searching for evidence of habitability and life within our Solar System. However, the science of biosignatures—the detection and interpretation of signs of extant or extinct life—remains incomplete. Here, we report a flight-ready, robust, agnostic molecular biosignature detection technique based on pyrolysis–gas chromatography–mass spectrometry (py–GC–MS) combined with machine learning. To develop this technique, we used py–GC–MS to collect rich chemical spectra from hundreds of carbon-rich samples, including but not limited to: biological specimens from all three domains of life, taphonomically altered/fossilized life forms, carbonaceous meteorites, and laboratory organic synthesis experiments. We trained a machine learning algorithm on the presence, absence, and magnitude of tens of thousands of unique chemical features in the dataset. The final algorithm can: (1) predict the biogenicity of an unknown sample to greater than 90% accuracy, (2) detect signs of life even when biotic matter is mixed with organics of abiotic origin, and (3) discriminate among kinds of biota, such as photosynthetic vs. non-photosynthetic life. We hope to use our technique on future astrobiology missions to identify “potentially biological anomalies,” i.e., possible signs of life with non-Earthly biochemistry. Similar machine learning approaches may be applicable to other kinds of instruments, and to create a unified framework for biosignature assessment that takes into account data from multiple analytical instruments at once. Overall, our general technique has the potential to serve life-detection missions to the diverse rocky worlds of our Solar System.

Sebastiaan Krijt (University of Exeter)

The properties of planetary systems depend sensitively on the physical and chemical structure of the protoplanetary discs in which they form. At the same time, the processes associated with planet formation can dramatically influence the evolution of protoplanetary discs. In this talk, I will focus on the ways in which planet formation via core accretion can shape the chemical environment of growing protoplanets. In particular, I will discuss the consequences of dust coagulation, pebble drift, planetesimal formation and pebble accretion on gas-phase molecular and elemental abundances, highlighting exciting ongoing efforts to study the signatures of these processes with ALMA and JWST.

Katherine de Kleer (Caltech)

Tides are a key internal energy source for numerous Solar System moons as well as exoplanets, driving their chemical evolution, geological activity, and even habitability. At Jupiter’s moon Io, tides power dramatic volcanism accompanied by outgassing at a rate of thousands of kg/s. Io orbits deep within Jupiter’s magnetosphere, resulting in mass-loss from these outgassed species that impacts Io’s chemical evolution and populates large-scale plasma and neutral particle structures around Jupiter. The processes of tides, mass-loss, and chemical evolution are relevant to many worlds both within our Solar System and beyond, and Io can serve as a template for better understanding them more broadly. Yet despite decades of study, major questions remain about Io’s formation, evolution, and even its current state. In this talk I will discuss our current understanding of Io, focusing on recent results from telescope and spacecraft observations, and will highlight unanswered questions and prospects for addressing them in the coming years.

Michael Way (NASA/GISS, Uppsala University)

In recent years a great deal of work has appeared related to better quantifying Venus' evolutionary path from Magma Ocean to present day Hell House world. We will present the latest results on these evolutionary histories and discuss recent work reanalyzing the Pioneer Venus in-situ neutral mass spectrometer data. The latter is one of the few in-situ atmospheric measurements of Venus, whose results have direct implications for constraining Venus' climate history, and providing temporal data to be compared with the upcoming Venus DAVINCI mission to launch in 2030.

Joshua Krissansen-Totton (University of Washington)

Early JWST observations of hot rocky exoplanets have revealed that many of these objects may be airless rocks. For example, JWST observations of TRAPPIST-1b [1] and c [2] disfavor substantial atmospheres containing CO2. Given the similar densities of all TRAPPIST-1 planets, and the theoretical potential for atmospheric erosion around late M-dwarfs, this observation might be assumed to imply atmospheres are also unlikely for the outer planets. Here, we present a new, self-consistent model of atmosphere-interior evolution during the transition from primary to secondary atmospheres to show that this may not be the case. The model incorporates all Fe-C-O-H-bearing species and simulates magma ocean solidification, radiative-convective climate, thermal escape, and mantle redox evolution. For our illustrative example TRAPPIST-1, our model strongly favors atmosphere retention for the habitable zone planet TRAPPIST-1e. In contrast, the same model predicts a comparatively thin atmosphere for the Venus-analog TRAPPIST-1b, which would be vulnerable to complete erosion via non-thermal escape and is consistent with JWST observations. This difference arises because the duration of hydrodynamic escape on planets exterior to the runaway greenhouse limit is limited, and because surface water inventories are readily replenished by the reduction of FeO by H2. More broadly, we suggest that habitable zone planets around M-dwarfs such as TRAPPIST-1 are highly likely to retain secondary atmospheres across a broad swath of initial compositions, a prediction that is imminently testable with JWST.

[1] Greene, T. P., et al. (2023). Nature, 618(7963), 39-42.

Jayne Birkby (University of Oxford)

High resolution cross-correlation spectroscopy (HRCCS) has proven a powerful and highly versatile tool in the characterization of exoplanet atmospheres. Its sensitivity to the position and shape of exoplanet spectral lines has enabled a rich exploration of exoplanet atmospheres over the last decade, from chemical abundances to the 3D dynamical nature of their winds and rotation. The era of the Extremely Large Telescopes (ELTs) will mark a step change for HRCCS, breaking into the regime of rocky exoplanets, with the potential to explore their atmospheres, and even their surfaces, in great detail across their diverse population, from outgassing lava worlds to biosignatures on habitable worlds. In this talk, I will give an overview of the rocky exoplanet science achievable with HRCCS using the first light and next generation instruments on the ELTs, beginning in 2029, highlighting several simulation studies that are vital in preparing us for this work. I will further discuss the challenges we face, from stellar astrophysics to laboratory work, and how we are tackling some of these with present day facilities. I will end with a discussion on the synergy needed between HRCCS, JWST, HWO, and LIFE to enable the fullest exploration of rocky exoplanets in the coming decades.

Renyu Hu (JPL Caltech)

JWST enables the measurements of the thermal emission spectra of small exoplanets to characterize their atmospheres and surfaces. Such measurements open up a new way to test models of atmospheric evolution and retention. I will present JWST thermal emission observations of a potentially rocky exoplanet, the planet 55 Cnc e, covering the wavelength range between 4 and 12 microns through two eclipse observations using the NIRCam/F444W and MIRI/LRS modes. Prior observations with Spitzer photometry showed that the planet must have either a volatile-rich atmosphere, or a molten lava surface shrouded by a mineral atmosphere while rotating at an asynchronous rate. The JWST observations have the sensitivity to distinguish the volatile-rich atmosphere scenarios versus the mineral atmosphere scenario via spectral features of H2O, CO, CO2, SO2, and SiO, providing one of the first direct detections of a non-H2-dominated atmosphere on an exoplanet. I will also discuss the challenges and mitigations for observing very bright stars using JWST.

Anna Mittelholz (ETH Zurich)

Planetary missions to Mars have enabled us to study its magnetic field environment - an important component of Mars’ history that is intertwined with virtually any other aspect of planetary evolution. Substantial progress was made when the MAVEN mission added wide-spread magnetic field coverage at lower altitudes than the previous MGS mission, and when InSight brought the first magnetometer to the Martian surface. I will discuss some recent findings from those missions and point out open questions. The most substantial step in future magnetic field exploration will be possible through regional exploration, e.g., with missions such as a Mars Helicopter.