Hazy or cloudy skies on the TRAPPIST-1 planets? Not with hydrogen.

I took laboratory results on exoplanet haze particles and input the physical parameters into a 1-D atmospheric model. I then compared the modeled results to Hubble observations of the Habitable Zone TRAPPIST-1 planets. I showed that hazy or cloudy hydrogen-rich atmospheres on these worlds aren't physically realistic based on lab constraints. This means these planets likely have heavier, secondary atmospheres (or no atmospheres at all!). 

Read my paper here: 

Or the preprint:

I also helped run atmospheric models for follow-up observations of TRAPPIST-1 g, getting similar results:

Finally, I ran the atmospheric models for the analysis that looked at the coldest, farthest out planet TRAPPIST-1h, and found again that its atmosphere isn't hydrogen-dominated or clear:

Exoplanet lab hazes are oxygen-rich, maybe good for clouds, and potentially full of life's building blocks.

I used mass spectrometry to understand the chemistry of exoplanet hazes made in the lab. I found that these hazes contain tons of oxygen, making them very different from "typical" Solar System hazes found in Titan's atmosphere. The hazes dissolved in polar solvents, which might make them good cloud condensation nuclei. I also identified chemical formulas consistent with amino acids, nucleobases, and sugars -- the building blocks of life. This means some exoplanet atmospheres alone can generate rich prebiotic inventories. 

Preprint here: 

Published version here:

We later did a follow-up experiment using a carbon dioxide-rich atmosphere with trace hydrogen sulfide gas -- we make organosulfur hazes! Read the paper here:

The hazes of Neptune's moon Triton are more oxygenated than Titan's and reveal the role of carbon monoxide in forming haze

I investigated the haze properties -- chemical, optical, and physical -- of a Triton-like haze made in the lab. I compared the Triton haze properties to those of other methane and carbon monoxide-rich nitrogen atmospheres, like those of Titan and Pluto. Carbon monoxide turns out to be very important! It affects the production rate (more haze!?), the composition (more oxygen! maybe makes glyceraldehyde, the simplest sugar? ), and the spectra (deeper spectral features from O-H bonds?). Future Neptune system missions should account for this complex chemistry in their instrument suites.

Read the preprint here:

Published version here:

Optical properties of exoplanet hazes and how they'll affect telescope observations

An ongoing project focuses on the optical properties of mini-Neptune, super-Earth, and terrestrial exoplanet hazes. The scattering and absorption by hazes will greatly impact the atmospheric spectra observed with current and future telescopes, like Hubble and JWST. We're also exploring whether stellar flares can alter these optical properties.

NEW: Our first set of optical properties for water-rich sub-Neptune hazes is now available. Please use them for all your modeling needs! (If you need assistance with this, please reach out to me, I'm happy to help).

Punchline: these oxygen-rich hazes can dramatically mute Hubble/IR exoplanet atmospheric measurements (in line with observations), but there should still be observable features! These exist both at longer IR wavelengths accessible to JWST and at shorter UV-Vis wavelengths that Hubble/UVIS can access. 

The interpretation of NIRCAM F322W2 data of WASP-39b, using a PICASO model grid I helped generate. Credit: Ahrer, Stevenson, Mansfield, Moran et al, Nature, 2023.

Atmospheric Modeling with PICASO

I spend a lot of my time running self-consistent radiative-convective thermochemical equilibrium (RCTE) atmospheric models - sometimes post-processed with aerosols and/or photochemistry - using the PICASO and Virga frameworks. 

These models help with the planning and interpretation of HST and JWST data. In addition to the TRAPPIST-1 planets above, planet-by-planet results include...

with more to come from several on-going JWST and HST programs...