Photochemical hazes are important opacity sources in temperate exoplanet atmospheres, hindering current observations from characterizing exoplanet atmospheric compositions. The haziness of an atmosphere is determined by the balance between haze production and removal. However, the material-dependent removal physics of the haze particles is currently unknown under exoplanetary conditions. Here we provide experimentally-measured surface energies for a grid of temperate exoplanet hazes to characterize haze removal in exoplanetary atmospheres. We found large variations of surface energies for hazes produced under different energy sources, atmospheric compositions, and temperatures. The surface energies of the hazes were found to be the lowest around 400 K for the cold plasma samples, leading to the lowest removal rates. We show a suggestive correlation between haze surface energy and atmospheric haziness with planetary equilibrium temperature. We hypothesize that habitable zone exoplanets could be less hazy, as they would possess high-surface-energy hazes which can be removed efficiently.

We perform the sessile drop contact angle measurements using a Rame-Hart goniometer using two test liquids (diiodomethane, ReagentPlus Sigma-Aldrich, 99% and HPLC water, Fisher Chemical) on 18 exoplanet haze analog samples and two substrates (quartz and mica disks). Images of the droplet profile were taken by the goniometer software. The images are processed using the contact angle plugin of ImageJ to extract the contact angle values.

The original droplet profile images can be found in each folder for a specific sample named with the sample name. The extracted contact angle data (in excel) file using ImageJ is also included in the folder for each sample. The data reduction folder has all the calculated surface energy values and the corresponding standard deviations using the Owens-Wendt-Rabel-Kaelble (OWRK) method for each sample.