JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY
ROSS-98 NRA 98-OSS-05Confirmation #:
Jun 15, 1998
The Galileo Photopolarimeter Radiometer (PPR) measured the first set of complete phase curves (polarization vs. phase angle) for the Galilean satellites, including the first such data for any
high-albedo icy body. Unique simultaneous photometry and polarimetry
at three wavelengths from 410 to 945 nm, together with unprecedented
mapping of Ganymede and Callisto offers a powerful data set for
investigating the surface texture of these diverse bodies in a manner
orthogonal to that provided by imaging and spectroscopy. Measurement
of the Moon during the Galileo Earth encounters verifies the behavior
of the PPR polarimetry.
Modelling of the polarization curves will proceed using code by
Mishchenko that allows realistic particle shapes, as well as a range
of sizes and refractive indices. Such modelling has shown promise in
reproducing atmospheric polarization behavior for the Earth. Goguen
established that techniques applicable to atmospheres are applicable
for high-albedo surfaces.
Analysis of the PPR data for the Galilean satellites will lead to
improved knowledge of the fine-scale surfaces of those bodies.
Correlation of mapped intensity/polarization behavior with existing
maps, imaging, and NIMS data will define local variations in the
style of surface alteration.
By providing new information about the surfaces of the Galilean
satellites, this work will:
1. Strengthen the set of clues available about the character of the
surfaces, and the mechanisms that produce them.
2. Stimulate foci for future NASA investigations by pointing out
regions of anomalous behavior.
3. Assist in future NASA robotic exploration by providing information
of engineering value, relevant to thermal, composition, and particle
We will fully calibrate the data set and derive final geometric
parameters, using the best available information, and archive with
the PDS high-level products such as phase curves and mapped images .
Recent relevant publications include:
"A quantitative test of the applicability of independent scattering
to high albedo planetary regoliths", Goguen, J. D., Icarus
(submitted, 1998; see Appendix). "Observing the Icy Jovian Satellites
with the Galileo Photopolarimeter Radiometer Instrument", L.K.
Tamppari, J.R. Spencer, T.Z. Martin, JGR Planets, 100, p. 18973
(1995). "Galileo Photopolarimeter Radiometer Observations of Jupiter
and the Galilean Satellites", G.S. Orton, J. Spencer, L. Travis, T.Z.
Martin, L. Tamppari, Science, 274, p. 389 (1996). "Observation
of Shoemaker-Levy Impacts by the Galileo Photopolarimeter
Radiometer", T.Z. Martin, G.S. Orton, L. Tamppari, L. Travis, and I.
Claypool, Science, 268, p. 1875 (1995).