P43A-2094
Discovering New Compounds on Icy Moon Surfaces with Mid-Infrared Spectroscopy

Thursday, 17 December 2015
Poster Hall (Moscone South)
Cindy L Young1, James J Wray1, Kevin P Hand2, Michael Poston3, Robert W Carlson2, Roger Nelson Clark4, John R Spencer5 and Donald E Jennings6, (1)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (2)Jet Propulsion Laboratory, Pasadena, CA, United States, (3)California Institute of Technology, Pasadena, CA, United States, (4)Planetary Science Institute Tucson, Tucson, AZ, United States, (5)Southwest Research Institute Boulder, Boulder, CO, United States, (6)NASA Goddard Space Flight Center, Greenbelt, MD, United States
Abstract:
Spectroscopy of icy satellite surfaces can aid us in understanding sources and sinks of material in the outer solar system. The spectral complexity of the Saturnian satellite system as seen in reflected sunlight suggests additional complexity may be present at mid-infrared wavelengths from which unique compositional information can be gleaned [1]. Yet to date, Cassini Composite Infrared Spectrometer (CIRS) surface compositional studies have received little attention.

We are investigating the value of mid-infrared spectroscopy for identifying non-H2O constituents of icy moon surfaces. On Iapetus’ dark terrain, we find an emissivity feature at ~855 cm-1 and a possible doublet at 660 and 690 cm-1 that do not correspond to any known instrument artifacts [2]. We attribute the 855 cm-1feature to fine-grained silicates, similar to those found in dust on Mars and in meteorites, which are nearly featureless at shorter wavelengths [3]. Silicates on the dark terrains of Saturn’s icy moons have been suspected for decades, but there have been no definitive detections until now. Because peaks can shift depending on temperature, pressure, and grain size, measurements at Iapetus-like conditions are necessary for more positive feature identifications [e.g., 4].

We measured the vacuum (P<3x10-8 torr) and low temperature (125 K) mid-infrared spectra of various fine-grained powdered silicates. We find that some of these materials do have emissivity features near 855 cm-1and match the doublet. Identifying a specific silicate would provide clues into the origin and implications of the dark material in the Saturnian system. We also report on our ongoing exploration of the CIRS icy moon dataset and plans for additional future measurements in JPL’s Icy Worlds Simulation Lab.

[1] Flasar, F. M., et al. (2004), Space Sci Rev, 115, 169.

[2] Young, C.L., et al. (in review), ApJ Lett.

[3] Christensen, P. R., et al. (2004), Sci, 306, 1733.

[4] Wray, J. J., et al. (2014), DPS 46th Meeting, Vol. 46.

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