Dr. Sarah Horst is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the University of Colorado. Due to the limitations of in situ measurements of planetary aerosols, and in particular the impossibility of in situ measurements in the cases of the atmospheres of the early Earth and extrasolar planets, laboratory experiments provide a necessary bridge between theoretical models of planetary atmospheres and the reality of their observed properties. The observed compositions of extrasolar planet atmospheres, and the poorly constrained composition of early Earth's atmosphere, indicate that laboratory experiments need to investigate organic molecule and aerosol production for a broader range of gaseous compositions than previously considered. The research proposed here will take advantage of the world-class aerosol simulation and analysis facilities at the University of Colorado to investigate the effect that oxygen has on aerosol formation and composition. This research will also investigate how choice of laboratory energy source affects aerosol formation and composition, which will further our understanding of the biases present in laboratory experiments and allow for more accurate application of the results of laboratory experiments to planetary atmospheres. Dr. Horst's research will improve our understanding of the range of planetary atmospheres where aerosols may form and increase our understanding of how oxygen is incorporated into organic molecules, which may have implications for the origin of life.
Dr. Horst will also work with the Division of Planetary Sciences of the American Astronomical Society and the NASA Science Mission Directorate to host a teacher workshop each year in conjunction with the annual DPS meeting. The teachers that attend the workshop will be paired with a planetary scientist or astronomer to interact with them and their students throughout the following year.
We have completed a number of fundamental studies of haze formation in planetary atmospheres. In summary, we have examined the effect of energy source on haze formation in the laboratory and demonstrated that nitrogen is efficiently incorporated into planetary atmospheric hazes using either photons or energetic plasmas. We have also measured the density of Titan aerosol analogues, a parameter that is important for modeling of both atmospheric (clouds, radiation transport) and surface (sediment transport by wind and rain/streams) processes. We investigated the effect of the inclusion of oxygen bearing molecules on haze formation and found that the addition of CO increases the amount of haze particles produced and the amount of oxygen incorporated into the particles. Additionally, work with O2 indicates that haze may have been present in the atmosphere of the early Earth during the rise of oxygen. Taken as a whole, the findings described here have altered our understanding of aerosol formation in planetary atmospheres. The results point towards multiple pathways for haze formation based on the composition of the available gas phase precursors. We have experimentally demonstrated that the range of atmospheres for which haze may be present is greater than is often assumed and therefore the range of possible haze composition is also greater than previously believed. As spectra of more and more exoplanets are obtained, it is increasingly clear that "hazy" atmospheres may be the norm, supporting the idea that haze forms frequently, under a broad range of atmospheric conditions. Futher work will serve to elucidate the pathways leading haze formation and aid in the development of fundamental requirements for the formation of haze in planetary atmospheres. The project provided many opportunities for the PI to learn new experimental and data analysis skills (including aerosol mass spectrometry, proton transfer mass spectrometry, construction and operation of vacuum systems, use of high pressure gas manifolds, aerosol collection, etc.). Additionally, the PI gained experience mentoring graduate students. Early in Year 3 of the project, the PI was offered and accepted a position as an Assistant Professor in the Department of Earth and Planetary Sciences at Johns Hopkins (started September 2014). The Project therefore played an important role in the retention of the female PI who is a member of an underrepresented group. In addition to the impact on the PI, the project also supported a series of teacher workshops concurrent with the annual meeting of the Division for Planetary Sciences (DPS) of the American Astronomical Society. The first three workshops, held in Reno, NV, Denver, CO, and Tucson, AZ were very successful serving a total of 70 K12 STEM teachers. With the completion of three successful workshops, the project stablished a sustainable model for this type of workshop and DPS intends to continue these workshops in the future (with some degree of involvement from the PI).
