Research Project R. Signorell

The atmosphere of early Earth contained organic haze layers that likely impacted planetary habitability, surface UV shielding, and the delivery of prebiotic molecules. Laboratory analogs of these hazes, known as tholins, contain aldehyde and nitrile groups that serve as the principal precursors for Strecker synthesis of amino acids, so understanding haze properties is directly tied to understanding the origins of life's building blocks. Recent work confirms that key chemical precursors for amino acid synthesis, such as aldehydes and nitriles, can form directly as solids within these atmospheric layers. However, two critical parameters, the imaginary part of the refractive index, which governs how strongly particles absorb light, and the way particle size responds to relative humidity, remain poorly constrained for different atmospheric compositions and redox states. 

To address these gaps, this project will use a novel single-particle laser trap to isolate and study individual tholin aerosol particles ranging from 20 nm to 1 µm, produced under a range of CO2/CH4 ratios. By combining optical levitation with broadband light scattering, Brownian motion spectroscopy, and Raman fluorescence spectroscopy, this approach allows the team to measure both the real and imaginary parts of the refractive index of realistic haze particles, while quantifying how relative humidity drives particle growth via water uptake. Furthermore, the experiment will track how continuous UV irradiation alters the particles' chemical bonds, size, and long-term aging dynamics. Tholin samples will be synthesized using the PAMPRE plasma reactor at LATMOS in Paris and the UV photochemistry setup at ETH D-EAPS, covering a realistic range of particle sizes and redox conditions. The resulting refractive indices and growth factors will be integrated into early-Earth climate models to clarify how atmospheric hazes modulated surface temperatures, cloud formation, and the overall UV flux, parameters essential for defining the surface environments where life first emerged and persisted.