Airless Solar System Objects
Recent discoveries revealed that the planet Mercury has a tenuous atmosphere which is supplied by material desorbing from its surface. Several energetic phenomena which originate from the sun and solar wind's interaction with the surface are thought to be responsible for removing both neutral and ionic chemical species. Laboratory experiments are being performed to determine the role of each of these phenomena including: electron-stimulated desorption (ESD), photon-stimulated desorption (PSD), proton-induced sputtering, and thermal desorption processes on comparable regolith, the layer of loose material on a planetary body. These experiments utilize several mass spectrometric techniques which are performed in custom built ultrahigh vacuum chambers. Determining the contributions from these interactions is important in understanding the formation of Mercury's tenuous atmosphere. The experimental data obtained can be used to help identify the composition of minerals and/or rocks in the regolith. These data can also be extrapolated to other airless bodies, e.g., moons, asteroids, and even man-made spacecraft, to better understand space weathering processes.
The presence or absence of water is not only important to humanity's understanding of our solar system, but is also an important parameter in choosing targets for space exploration. Recent spacecraft[1,2,3,4] measurements have shown the presence of water and ice in places previously thought to be completely dessicated. Our experiments make use of Temperature Program Desorption (TPD) measurements to determine the desorption energy and kinetics of water on lunar regolith surrogates. These data are useful for modeling water stability and transport on the Moon and other airless bodies. Meanwhile, our collaborators at the John Hopkins University Applied Physics Lab (APL) are conducting Diffuse Reflectance Spectroscopy Measurements under Ultra-High Vacuum (UHV) from the Infrared (IR) through the Vacuum Ultra-Violet (VUV) frequency range and at temperatures ranging from 100 to 700 K. These data are vital for interpreting spectral observations of both water and other volatiles on airless bodies. Finally, ion beam studies seek to unravel the physical and chemical details involved in proton- induced hydroxylation and possible water formation on and within lunar regolith materials.
-  Colaprete, A., et al. (2010) Science, 330, 463-468.
-  Clark, R. N. (2009) Science, 326, 562-564.
-  Pieters, C. M., et al. (2009) Science, 326, 568-572.
-  Sunshine, J. M., et al. (2009) Science, 326, 565-568