Cayman T. Unterborn (Southwest Research Institute)

Classifying small exoplanets as rocky, volatile-rich, or iron-enriched is a prerequisite for efficient allocation of atmospheric characterization resources. The Nominally Rocky Planet Zone (NRPZ) provides a framework for this classification by comparing observed bulk densities against the expected density range for volatile-free rocky planets, calibrated from stellar abundance distributions. However, the efficacy of the NRPZ is critically dependent on the precision of the underlying mass and radius measurements. Here, we perform an analytical propagation of observational uncertainties through the NRPZ classification framework for 37 candidate rocky exoplanets with radii below 2 Earth radii orbiting stars with visual magnitudes less than 11. Of these 37 planets, we find 11 of them currently have mass and radius uncertainties to definitively classify them as Mini-Neptunes or Super-Mercuries. The remaining planets, however, require extreme reductions in current mass and radius uncertainties, together, to classify them as either leaning rocky or not rocky. We further quantify the number of orbits needed to be observed for these planets to achieve these lower uncertainties, finding an average of ~2000. We argue that, while possible, this level of intense observation is likely not feasible for many of these planets and that mass-radius models alone are not likely to allow us to classify all but those planets with outlier densities. We propose that only through observations that reveal the presence, or lack thereof, of a significant atmosphere through characterization via JWST or next-generation telescopes will we definitively classify many intermediate density exoplanets as rocky. I will conclude the talk with a comparison of these results to our best-resolved exoplanet system: TRAPPIST-1 and discuss that while many planets may not yield habitable, or even temperate planets, we show that they can still provide utility in our understanding of planets as a whole, and exactly what it takes to build Earth-like worlds.

Eleonora Alei (NASA Goddard Space Flight Center)

One of the primary goals of the astronomical community in the next few decades is to characterize temperate terrestrial exoplanets to search for life. To address this challenge, the US Astro2020 Decadal survey recommended the pursuit of a technical and scientific study for the Habitable Worlds Observatory (HWO), an ultraviolet/visible/near-infrared (UV/VIS/NIR) “high-contrast direct imaging mission with a target off-axis inscribed diameter of approximately 6 meters” which shares design and technology heritage with the previous concept studies HabEx (Habitable Exoplanet Observatory) and LUVOIR (Large UV/Optical/IR Surveyor). Similarly, European scientists focus on the development of the MIR space-based nulling interferometer LIFE (Large Interferometer For Exoplanets).

These observatories would focus on complementary regions of the electromagnetic spectrum: HWO will explore the reflected light spectrum regime in the UV/VIS/NIR, while LIFE would capture the planetary thermal emission in the MIR. Both wavelength ranges provide us with their specific set of preferred information and come with specific drawbacks. Yet, the scientific yield of synergistic observations in the UV/VIS/NIR+MIR range has the potential of being greater than the sum of its parts: having access to multiple spectral windows into the atmosphere of a potentially habitable planet could be transformative for the search of life in the universe.

Shang-Min (Shami) Tsai (ASIAA)

In this talk, I will discuss how atmospheric chemistry and formation pathways shape sub-Neptune atmospheres, and how observed spectra can be used to learn their interior structure and potential habitability. Using the temperate sub-Neptune K2-18 b as a case study, I will highlight several diagnostics that can be generalized to the broader population. I will examine how orbital dynamics and cloud formation modulate observable water signatures, and present an agnostic framework to test chemical consistency in order to distinguish between different interior structures. I will conclude with an outlook on key concepts and directions for future studies.

Ana-Catalina Plesa (DLR)

Over the past decades, large-scale numerical simulations of interior evolution have grown to become one of the most powerful approaches to model the interior of planetary bodies in our Solar System and beyond. Geodynamic models are used to investigate the evolution of the interior that ultimately affects the distribution of seismic velocities, surface heat flow, and partial melting of the mantle. Combined with constraints derived from planetary mission data and laboratory experiments, these models help us to improve our understanding of the history and present-day thermal state of planetary interiors.

Miki Nakajima (University of Rochester)

Lisa Dang (Université de Montréal)

Moa Persson (Swedish Institute of Space Physics)

Day 1 of the fourth edition of the biennial Rocky Worlds conference

The planets that are best understood are the four terrestrial planets of our own solar system. Applying the detailed understanding gleaned from these bodies is crucial in our interpretation of exoplanetary systems. With the ongoing programs to search for planets around nearby stars, as well as upcoming ground- and space-based surveys, we can anticipate huge growth in the number and information on detected rocky exoplanets in the coming decades. As the characterisation of these new planetary systems proceeds it will in turn improve understanding of our own solar system, and in particular of how potentially habitable Earth-like planets may form, evolve, and are distributed throughout the galaxy.

The Rocky Worlds Meeting Series aims to bring together planetary scientists, astronomers, and earth scientists to foster discussion and build the collaborations that will pave the way for the next decade of rocky exoplanet discovery and characterisation.

Schedule: https://groningen2026.rockyworlds.org/programme/schedule

Annelies Mortier (University of Birmingham)

Diogo Lourenco (ETH Zurich)