P011-08
The surface energies and lifetimes of cool exoplanet haze analogs: insight from laboratory experiments

Monday, 7 December 2020: 16:28
Virtual
Xinting Yu1, Xi Zhang2, Sarah M Horst3, Chao He3 and Patricia McGuiggan4, (1)University of California Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States, (2)UC Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States, (3)Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD, United States, (4)Johns Hopkins University, Department of Materials Science and Engineering, Baltimore, MD, United States
Recorded Presentation
Abstract:
Photochemical hazes are shown to greatly impact current exoplanet atmospheric characterization by muting spectral features [e.g., 1, 2], however, they remain poorly understood due to their complex chemical nature. We measured a bulk material property, the surface energy, for a matrix of laboratory-produced cool exoplanet haze analogs [3, 4] with the contact angle method. The surface energy of the hazes can reveal their bulk chemical make-ups, cohesiveness, and wetting properties (relevant for haze-cloud interactions).

We measured a wide range of surface energy values (between 25-70 mJ/m2) for these haze analog samples, indicating a diverse range of chemical make-ups and cohesiveness. We find energy input, atmospheric composition, metallicity, and temperature all have strong impacts on the final surface energies/chemical make-ups of the haze analogs.

The haze produced with higher-energy densities (through cold plasma discharge) have a wider range of surface energies (25-70 mJ/m2), while the surface energies of the lower-energy irradiated (far UV photons) hazes have a smaller range and are all relatively high (55-70 mJ/m2). For H2 (low metallicity) and CO2 (high metallicity) dominated atmospheres, the plasma haze samples tend to have low surface energies (25-40 mJ/m2), are dominated by mainly non-polar structures, and are also hydrophobic. Because of their low surface energies and hydrophobicity, these haze particles likely have long lifetimes in the atmosphere and are difficult to be removed efficiently by both dry and wet deposition. We propose that hydrophobic hazes could be common on very hazy exoplanets such as GJ1214b. The H2O dominated plasma haze samples and all the UV haze samples tend to have high surface energies (50-70 mJ/m2), are more polar and thus hydrophilic. We propose that for habitable exoplanets with condensable water in a stable low energy stellar environment, the produced hazes are more likely to be hydrophilic and has shorter lifetime in the atmosphere, making these atmospheres potentially clearer for future spectral characterization.

[1] Kreidberg, L., et al. 2014, Nature, 505, 69.

[2] Knutson, H. A., et al. 2014, Nature, 505, 66.

[3] Hörst, S. M., et al. 2018, Nat. Astron., 2, 303.

[4] He, C., et al. 2018, AJ, 156, 38.

<< Previous Abstract | Next Abstract