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    MEASUREMENT OF NANOPARTICLE SURFACE ENERGIES WITH APPLICATION TO NUCLEATION AND CONDENSATION IN EXOPLANET ATMOSPHERES
    Megan Householder1; Alexandra Navrotsky1; Kristina Lilova2;
    1ARIZONA STATE UNIVERSITY, Phoenix, United States; 2ARIZONA STATE UNIVERSITY, Tempe, United States;
    PAPER: 52/Geochemistry/Regular (Oral) OS
    SCHEDULED: 14:00/Tue. 28 Nov. 2023/Coral Reef



    ABSTRACT:
    Exoplanets orbit stars other than our own sun. Aerosols are a prominent feature of exoplanet atmospheres, sometimes obscuring the spectral determination of atmospheric gas composition [1]. Hot Jupiters are studied because they are the hottest of exoplanets, so emit the most radiation and therefore, give the most spectral information on exoplanets. Because it is not yet possible to definitively determine aerosol composition and formation through astronomical observations, it is important to model aerosol production accurately [2]. A key factor in the determination of nucleation and condensation rate is the surface energy of the nucleating material [3]. High surface energy materials, such as forsterite, will nucleate much more slowly compared to lower surface energy materials, such as sulfides. Despite their importance, few surface energies of rock-forming minerals have been measured [4]. In this work, surface energies were measured using oxide melt solution calorimetry of materials with different surface areas for likely exoplanet atmosphere condensates including zinc sulfide (ZnS) [5] and enstatite (MgSiO3), with other measured surface energies taken from experimental rather than estimated data. This work inputs the accurate measured surface energy data to calculate a model of nucleation rates for each of the proposed cloud species of a hot Jupiter exoplanet with atmospheric metallicity of 10x solar, a total atmospheric pressure of 10 bar and a saturation ratio of 10. These corrected surface energy values show drastically different nucleation rates for a variety of condensates in the atmospheres, which lead to different atmospheric compositions of these exoplanets than previous models.

    References:
    [1] D. Adams, P. Gao, I. de Pater, and C. V. Morley, “Aggregate Hazes in Exoplanet Atmospheres,” Astrophys. J., vol. 874, no. 1, p. 61, Mar. 2019, doi: 10.3847/1538-4357/ab074c.<br />[2] A. Navrotsky and M. Householder, “New worlds, new chemistry, new ceramics,” Int. J. Ceram. Eng. Sci., vol. 3, no. 6, pp. 252–266, Nov. 2021, doi: 10.1002/CES2.10104.<br />[3] P. Gao, M. S. Marley, and A. S. Ackerman, “Sedimentation Efficiency of Condensation Clouds in Substellar Atmospheres,” Astrophys. J., vol. 855, no. 2, p. 86, Mar. 2018, doi: 10.3847/1538-4357/aab0a1.<br />[4] S. Chen and A. Navrotsky, “Calorimetric study of the surface energy of forsterite,” Am. Mineral., vol. 95, no. 1, pp. 112–117, 2010, doi: 10.2138/am.2010.3339.<br />[5] T. Subramani, K. Lilova, M. Householder, S. Yang, J. Lyons, and A. Navrotsky, “Surface energetics of wurtzite and sphalerite polymorphs of zinc sulfide and implications for their formation in nature,” Geochim. Cosmochim. Acta, vol. 340, pp. 99–107, 2022, doi: 10.1016/j.gca.2022.11.003.