Ground-Based Near- and Mid-IR Observations of Saturn's Rings: Azimuthal Asymmetries in Ring A.
Abstract
We initiated an observational campaign of near- and mid-infrared spectrophotometry of Saturn's main rings from the 1995 Earth -- Saturn ring plane crossings epoch. We acquired data at the NASA/InfraRed Telescope Facility (IRTF) from 1995 to 2002 with NSFCAM, a 1-5 μ m camera, and MIRLIN, a 10-μ m camera, at several diagnostic wavelengths spanning the spectral interval from 1.58- to 24-μ m. Our observational program has, therefore, covered nearly one third of a Saturnian year, following the progressive march of the rings from their edge-on presentation at the equator in 1995 (vernal equinox) to their maximum opening, obscuring the northern pole of Saturn (southern summer solstice). Our specific scientific objectives are to determine near-infrared reflectivity, brightness temperature, thermal inertia, opacities of the rings and azimuthal/ansae asymmetries. Our preliminary results indicate that the brightness temperature of the rings peaks near 18 μ m, with a east/west ansae asymmetry of few degrees, similar to the near-infrared reflectivity asymmetry. Our current efforts are aimed at modelling Ring A near-infrared reflectivity and thermal properties as function of solar elevation (or ring opening angle ROA from 0 to 26o), inclination and phase angle to gain insight into the nature of the ring particles. Over the range of ROA, particles in Ring A experienced thermal heating and cooling as they entered and exited Saturn shadow. In 2003-04, Ring A was outside the planetary shadow, not experiencing any thermal cooling nor heating, thereby allowing the decoupling of planetary shadow effects and azimuthal heterogeneities.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #36
- Pub Date:
- November 2004
- Bibcode:
- 2004DPS....36.1907Y