Seminars at FGG
Ice Species on TNOs: A Case of Nature vs Nurture
Speaker: Brittany Harvison ( (University of Central Florida, Orlando, Florida, USA))
Date and time: 2026-04-20 11:30
The Solar System is rich in evolutionary history, from the inner terrestrial planets to the outer gas giants. Over the past three decades, since the discovery of Albion, the first Trans-Neptunian object (TNO) since Pluto, icy planetesimals known to exist beyond the ice giant Neptune have attracted particular interest. Objects ranging from roughly 40 to thousands of astronomical units (AU) from the Sun have surfaces rich in various ice species. These species originate from the protoplanetary disk, and their distribution across TNO surfaces today reflects the molecular footprint of the disk during planetary formation. Since the TNO population is situated far from Earth and mostly consists of objects smaller than 1000 km in diameter, obtaining high-quality ground-based observations is relatively difficult. With the James Webb Space Telescope, the scientific community now has unrestricted access to the icy surfaces of TNOs in the 0.8–5.2 μm range. Analyzing over 50 medium-sized TNOs (97–792 km) has identified three compositional groups, helping to reveal the composition of the protoplanetary disk before any orbitally disruptive events (Pinilla-Alonso et al. 2025). These groups are called the “Bowl,” “Double-Dip,” and “Cliff,” named after the shape of their 3 μm region. The “Bowl” type features strong water-ice signatures, weak CO2 ice features, and the reddening and darkening effects of silicates. The “Double-Dip” spectrum is dominated by signatures of carbon oxides, primarily CO2 and CO, coexisting with some complex organics. The “Cliff” is characterized by a chemically evolved surface, which results in spectra showing clear evidence of complex organics with -CH, -NH, and -OH features, methanol, and CO2. Although the previous work presents a scenario where the main driver for the three groups is the presence of ice lines in the protoplanetary disk, evolutionary effects are also essential in determining the current surface composition of icy bodies. Space weathering processes are evident in numerous bodies, such as the presence of H2O2 in the “Bowl” (Harvison et al., 2025), CO in the “Double-Dip” and “Cliff” (Henault et al., 2025), and light hydrocarbons on dwarf planets (Emery et al., 2024). Additionally, thermal effects on icy surfaces are demonstrated in the exploration of Centaurs (Licandro et al., 2025). Meanwhile, geothermal processes lead to the depletion of the D/H ratio on the surfaces of Eris and Makemake (Grundy et al., 2024; Glein et al., 2024). In this presentation, we will examine the spectral features that identify the ice species on objects thought to originate from the farthest regions of the protoplanetary disk, where these objects once existed within the compositional gradient, as indicated by their dominant molecular species. We will also discuss the various processes that influence the balance between nature and nurture on the surface of Trans-Neptunian objects.