Rachel M. E. Mastrapa Curriculum Vitae:  Rachel studies the surface processes of icy Solar System bodies by interpreting their infrared spectra. The majority of her work involves performing the ground truth measurements in the laboratory including calculating the complex indices of refraction of single composition ice samples. These measurements are then used to construct model spectra to interpret the chemical composition of observed spectra. She also studies the subtle changes seen in ice mixtures that are not seen in single composition samples. She has helped measure the surface binding energy of the CH4-H2O-ice system, which can be used to measure the residence time of CH4 on H2O-ice rich surfaces. Finally, she has measured how proton irradiation can change the phase of H2O-ice from crystalline phase to amorphous phase. Rachel has collaborated with her peers to collect spectra of Europa from the Keck Observatory and interpret Cassini VIMS spectra of Enceladus.
Projects
Molecules in Ice and Meteorites
NNX07AE34A
The purpose of our proposed research is to investigate the formation and distribution of ices and organic molecules in space. Since tons of organic molecules come to Earth every day from space, and the mass may have been a million times more on the prebiotic Earth, such molecules may have contributed to the origin of life on Earth. By extension, this exogenous delivery process may be generally applicable to the development of life on the planets of other stellar systems, and thus is of fundamental importance to SETI. This program focuses on ice experiments for comparison to Solar System objects, meteoritic organics, and interstellar dust particles (IDPs). We also are actively pursuing related observational and theoretical projects through collaborations with other scientists at NASA, universities, and non-profits.
Detailed Studies of Amorphous and Crystalline Ice in the Solar System
NNX08AY45G
Water ice spectra have been obtained from many outer solar system objects, where they have proved useful in determining surface properties such as temperatures, grain sizes, and the presence of trace contaminants. In some cases, the presence of amorphous vs. crystalline ice has been used to interpret the recent thermal and radiation his-tory of the surface [Hansen and McCord 2004]. The goal of this proposal is to carefully quantify the conditions under which amorphous and crystalline ices are formed and apply that knowledge to icy objects in the outer solar system.
The tasks covered in this proposal consist of (a) acquiring near-IR spectra of galilean, saturnian and uranian satellites, including Galileo/NIMS and Cassini/VIMS spectra, (b) modeling the surface environments (temperature and UV/charged particle fluxes) associated with local spectra observations, and (c) develop rules based on these real-life laboratories for the amorphization and crystallization rates of H2O-ice. The presence of amorphous ice on the warm surfaces of Europa and Ganymede is currently an unexplained problem, as is the near-ubiquitous presence of crystalline ice on the surfaces of Charon, several Kuiper belt objects, and the large uranian satellites. If the rates of amorphization and crystallization were understood in the context of relevant solar system environments, then the observed state of H2O-ice on remote objects might serve as useful constraints on the recent history of those objects.
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