Sarah Rugheimer

Characterizing the atmospheres of temperate, terrestrial exoplanets requires high-sensitivity mid-infrared (MIR) observations. As a member of the Large Interferometer for Exoplanets (LIFE) science team and former co-lead of the Project Office, I work on defining the mission requirements for detecting habitability markers.

My recent work addresses the "Goldilocks problem" of water detection. Using the LIFESIM tool and Bayesian retrievals, we explore how different atmospheric water distributions—from vertically constant profiles to Earth-like "cold trap" distributions—impact our ability to constrain water abundances (Rugheimer et al. 2026). In the highest water cases, the water features saturate the spectrum and hides its own signal. We are able to detect water at abundances a few orders of magnitude above and below modern Earth's.

This builds on our previous work (Konrad et al., 2022; Alei et al. 2022) evaluating the diagnostic potential of MIR interferometry for studying Earth throughout its geological history, from the prebiotic era to the modern day.

Water Posteriors from Rugheimer et al. 2026

While my primary focus is on habitable worlds, studying extreme environments like Ultra-Hot Jupiters (UHJs) allows us to test atmospheric physics at its limits. My graduate student Esther Wang performed a re-analysis of archival HST/STIS spectroscopy of the highly irradiated gas giant WASP-178b (Wang, Rugheimer, & Dittmann 2026).

We achieved the first direct spectroscopic detection of Silicon Monoxide (SiO) in this atmosphere. At equilibrium temperatures near 2470 K, normally refractory elements like silicon remain gaseous, providing unique spectral features in the near-UV that help us understand the chemical diversity of the galaxy.

UV spectra of WASP-178b showing in-band/out-of-band technique from Grant et al. 2023 applied to archival HST data in Wang et al. 2026

Adding in-band vs out-of-band yields different transit depth showing detection of SiO from Wang et al. 2026

The majority of planets currently identified in the "habitable zone" orbit M-dwarf stars. However, these stars have vastly different UV environments than our Sun. I model how the high-energy stellar radiation impacts the photochemical production and destruction of biosignature gases like Ozone (O₃) and Methane (CH₄). I research techniques to remotely detect life in the atmospheres of extrasolar planets. The focus of my work has been on how spectral type and stellar activity will influence the photochemistry and therefore the resulting detectable spectral features in terrestrial planets. I use a 1D coupled climate and photochemistry model and a line-by-line radiative transfer model to do forward modeling of direct and transit detection spectra with a particular focus on biosignatures of potentially habitable Earth-like planets.

I developed a spectral database for F through M stars (2300K–7000K) and Earth-analogs across four geological epochs. For FGK stars, I integrate IUE satellite UV data with theoretical models to study atmospheric impacts on Earth-like planets. To address the challenges of M-dwarfs—which remain active longer despite low luminosity—I modeled both active and inactive states, including six 'quiescent' stars using Hubble UV observations from the MUSCLES program.

The relative absorption in the IR for biosignatures around active and inactive M9V stars (see Rugheimer et al., 2015).

IR spectra for an Earth-like planet for four geological epochs showing possible biosignature progression under different stellar environments (see Rugheimer & Kaltenegger 2018).

My work in Rimmer & Rugheimer 2019 we considered the formation of prebiotically interesting molecules, such as HCN, NH₃, CH₄, and C₂H₆ in an early-Earth type atmosphere. Some of these molecules could be produced abiotically in a CO₂/CH₄/H₂ rich atmosphere with lighting and photochemistry. And the carbon to oxygen ratio of a planetary system will determine the bulk atmosphere composition, outgassing, and the types of species that will form through photochemistry. These molecules would be interesting to detect in an exoplanet atmosphere since they are known to be useful for key prebiotic chemical pathways. HCN, for example, is present at each of the initial photochemical reactions that produce lipids, amino acids and nucleosides, the three building blocks of life (Patel et al. 2015).

Pre-biotic atmosphere bulk composition, outgassing and photochemically produced species will depend on C/O ratio (from Rimmer & Rugheimer, 2019).