Plenary Lectures and VIP Guests

Dr. Megan Householder

Abstract:

Amorphous forsterite (Mg₂SiO₄) is one of the most common silicates composing aerosol clouds in hot giant exoplanetary atmospheres such as VHS 1256b and WASP-107 b. Water and carbon dioxide are found throughout exoplanetary atmospheres and their spectra are muted by aerosols such as forsterite. Here, we present the first calorimetric measurements of the enthalpies of water and carbon dioxide adsorption on the surface of amorphous forsterite nanoparticles. This measurement will give insight into how water and CO₂ interact with silicates and the conditions where condensation on aerosol clouds occurs. Amorphous forsterite was synthesized using the sol-gel method and subsequently microwaved to produce nanoparticles. Characterization was performed with Fourier transform infrared spectroscopy, X-ray diffraction spectrometry, thermogravimetric and differential scanning calorimetry, surface area analysis using the Brunauer- Emmet-Taylor N₂ adsorption technique, scanning and transmission electron microscopy, energy dispersive spectroscopy, and adsorption calorimetry. We find that amorphous forsterite has strong bonds to water at the chemisorption level, and prefers to bond to water instead of carbon dioxide. Amorphous forsterite saturates early with H-O at active sites caused by lack of long-range ordering, dangling Mg, or broken Mg-O. Another explanation can be residual water which already occupies the highest energy active sites. The residual water in the nano amorphous forsterite most likely facilitated the formation of strongly bound carbonate/bicarbonate species, therefore reducing the number of available adsorption sites for CO binding. In this talk I will discuss these laboratory investigations and implications regarding water and carbon dioxide adsorption enthalpies on amorphous forsterite in warm and hot exoplanet atmosphere spectra.