Uranian ring photometry: Results from Voyager 2
Abstract
We have investigated seven images of the Uranian rings taken with the clear filter of the Voyager 2 cameras during the January 1986 encounter. The images are at phase angles of 15.5°, 21.0°, 89,5°, and 172.5°. We obtained an average reflectivity (I/F) for each of the nine main rings (6,5,4,α,β,ɛ,γ,δ, and ɛ) at each phase angle. We compared the observed phase angle variation of I/F with model calculations for various combinations of macroscopic (backscattering) and microscopic (forward scattering) particles. The phase angle variation of I/F for all of the main rings is dominated by backscattering. The phase functions for the ring particles resemble that of the Moon; however, the observed phase functions decrease more rapidly between 21.0° and 15.5° than predicted by the lunar phase function. We obtained a single-scattering or Bond albedo for the large particles using the best fit backscatter phase function. The average Bond albedo of the particles for all the rings was 0.014+/-0.004. The shape of the phase variation of I/F around 172.5° phase angle was used to constrain the size distribution of the microscopic ``dust-sized'' particles. The fractional area in dust-sized particles in and around the main rings did not exceed 2×10-3. The observations are consistent with an average dust particle size of 1.0+/-0.3 μm in a Hansen-Hovenier distribution and with a power law distribution for spherical particles with spectral index (p)=2.5+/-0.5. The phase function of 1986U1R was not modeled, because of an anomalous azimuthal darkening in the highest phase angle image that could be due to structural variation.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- December 1987
- DOI:
- 10.1029/JA092iA13p14969
- Bibcode:
- 1987JGR....9214969O
- Keywords:
-
- Astronomical Photometry;
- Spaceborne Photography;
- Uranus Rings;
- Voyager 2 Spacecraft;
- Albedo;
- Astronomical Models;
- Interplanetary Dust;
- Radiative Transfer;
- Reflectance;
- Spacecraft Instruments