BRISSON Mid-IR Observations of the Moon and Galilean Satellites

The NASA BRRISON mission is performing observations of the Moon, Io, Callisto, as well as Jupiter, several asteroids, and comet Encke in addition to its primary target of comet ISON (1). The BRRISON mission will observe these secondary targets with its multispectral mid-infrared camera that is equipped with an astronomical R-band filter and an additional 8 filters, ranging from 2.5 microns to 4.6 microns, selected to characterize the peak and continuua of the CO2 and water emission bands from comet ISON (and Encke). These bands are also well positioned to characterize the hydroxyl/water absorption band in sunlight reflected from the surfaces of the Moon (2,3,4) and other airless bodies, as well as provide a multiple component temperature measurement of the thermal emission from them. The OH-related absorption bands on the Moon have already been characterized and mapped over the equatorial and mid-latitudes of the Moon (2,5), but at higher latitudes the band shape changes, broadening and possibly shifting to longer wavelengths. The later would be indicative of H2O. The multispectral capability of the IR instrument enables the BRRISON mission to determine if the molecule responsible for the 3-micron absorption band on the Moon can be attributed to H2O or if it is consistently and only OH, including mapping the distribution, depths, and shapes of the 3-micron band(s) over a significant portion of the Moon's nearside surface. Additionally, a possible change in OH- abundance with illumination/temperature has been observed by at least one of the three discovery spacecraft (2), but has not be further characterized by additional measurements. Because the BRRISON mission is planning to image a significant portion of the lunar surface, the multispectral measurements will be able to address that question as well. Third, surface temperatures will be calculated for the same pixels to enable exploring correlations between surface temperature and the 3-micron band characteristics. Surface temperatures will also be measured for other airless bodies, including the only non-icy Galilean satellite - Io. Additionally, the depth of the CO2 absorption feature on Callisto will be measured, to be compared with similar observations from Galileo NIMS and especially Cassini VIMS (6), which also obtained slightly subpixel observations of Callisto during its flyby of the Jovian system at the end of year 2000. (1) Cheng et al., AGU, 2013. (2) Pieters et al., Science, DOI: 10.1126 /science 1178658, 2009; (3) Sunshine et al., 10.1126/science.1179788, 2009; (4) Clark, R.N., 10.1126/science.1178105, 2009/; (5) McCord et al., JGR-Planets, VOL. 116, E00G05, doi:10.1029/2010JE003711, 2011; (6) McCord et al., Icarus 172 (2004) 104-126, 2013.