Tobi Hammond

Research Projects

I am interested in the habitability and atmospheric dynamics of transiting and non-transiting synchronously rotating terrestrial exoplanets and their resulting observational signatures.

Continents on M-Earths

Set of 5 figures of total surface weathering in Tmol per year using the WHAK calculation vs mean dayside surface temperature in Kelvin. Each subfigure represents the aqua and land planet continent configuration versions. Each plot shows 18 markers, 9 per land configuration. Colors represent instellations and marker shapes represent pCO2. 3 lines of best fit go through each instellation. The subfigures of the aquaplanet/landplanet and two nightside cases show flat slopes of dW/dT. The other 2 dayside cases have increasing dW/dT as instellation increases.
Plots of total weathering vs temperature for each continent configuration. Weathering sensitivity (dW/dT) with the WHAK calculation is highest for the dayside land cases and hotter surface temperatures. Overall, weathering sensitivity depends on the bulk amount of land and water availability (for precipitation).

In this project I wanted to examine the silicate weathering feedback on exoplanet. On Earth, this feedback contributes to long-term habitability and is crucial for applying the habitable zone to exoplanets. To do so, I varied the shape and location of continents on a synchronously-rotating, terrestrial, M-dwarf exoplanet using ExoPlaSim as well as changing pCO2 and incoming stellar flux. We find that the sensitivity of weathering depends primarily on the location of land and water relative to the substellar point, and, by extension, on the efficiency of dayside heat transport. Future work may include coupling ExoPlaSim to an interior model. Paper coming soon.

Observing Non-transiting planets with MIRECLE

MIRECLE is a telescope concept, similar to ESA’s LIFE, where its observing exoplanet’s thermal emission in the MidIR. Specifically MIRECLE will use the planet infrared excess (PIE) technique to separate the planets light from the star’s light. This can be used to observe nearby, non-transiting exoplanets. My goal was to simulate the climate and resulting emission spectra of nearby M-dwarf terrestrial exoplanet targets. We modeled five non-transiting targets using PSG and ExoCAM, as well as two more popular and farther away transiting targets. We find that the nearest and most temperate targets are the most detectable when modeling atmospheres of N2 and CO2. Additionally our PSG models show little sensitivity to observer inclination. Future work will apply CH4 and haze to the three nearest targets. Read Hammond et al (2025) here. Download the data on Zenodo here

Molecular SNR of CO2 for all seven planet targets across each pCO2 case. The closest planets within ~5 pc are above the 5 SNR detection threshold, indicated by a dashed line. Generally planet increase SNR with pCO2. SNR overall scales with system distance from Earth, with the exception of Teegarden c (3.8 pc) since its much colder than the other targets
Molecular SNR of CO2 for each planet target (colors and markers) across each pCO2 case. The closest planets within ~5 pc are above the 5 SNR detection threshold. Generally planet increase SNR with pCO2.

Obliquity on M-dwarf exoplanets

Global mean, max, and min (markers) surface temperature values for the four pCO2 cases (colors and linestyles) across obliquity. The black line indicates the melting point of water. Obliquity is a secondary effect on the global climate state to pCO2.

In this work, we vary obliquity on a synchronously rotating M-dwarf exoplanet. On such planets in single-planet systems it is typically assumed that the tidal forces impose a zero obliquity. However previous work has found that planets in compact, multi-planet resonant chains could sustain non-zero obliquity, although consensus varies on on the degree to which these planets would be tilted. Obliquity introduces a pseudo day-night cycle on M-dwarf exoplanet, which could have implications for the potential for life and wet-dry cycling. We use ExoCAM to assess the climate dynamics and habitability of TRAPPIST-1e in five obliquity state and four pCO2 levels. Varying obliquity has the most obvious effects on surface temperature patterns and by extension cloud cover. We find that sufficiently warm (i.e. cloudy) cases have distinguishable phase variation between obliquity states, but low phase amplitude. Read Hammond and Komacek 2024 here

Contact me at tobih12 at purdue dot edu