Measuring Centimeter-Sized Particles in the Saturnian Rings by Diffraction of Starlight
Abstract
Occultations of Saturn's rings have proven to be a useful way to measure the particle-size distribution of ring particles observed when in wavelength regimes where particles of different sizes behave differently. Studies of spacecraft-based radio occultations[1], Earthbased stellar occultations[2], and spacecraft-based solar occultations (Harbison et al., in prep.) have produced an understanding of the distributions of decimeter and meter-sized particles, and upper limits on the presence of micron-sized dust, but centimeter and millimeter-sized particles are less constrained. French and Nicholson also noticed in their stellar occultation work the presence of 'overshoots', places near a sharp edge of the rings, such as the Colombo, Maxwell, Huygens and Encke Gaps, where the transmission of starlight appears to exceed unity. They attributed this to starlight forward-scattered from the nearby ring into their detector. The Cassini spacecraft, in orbit about Saturn, has also been measuring stellar occultations with the Visible-Infrared Mapping Spectrometer (VIMS), with a total of 74 observed during the period 2004-2009. Similar overshoots ∼are seen in these data. Given that these overshoots are observed over ∼40 km from a typical distance of ∼ 400, 000 km, subtending an angle of 0.1 milliradian, at a wavelength of 2.92 μm, the particles that produce them must be of a size of ∼ ?/? or ∼ 3 cm. Thus, in this work, we are modeling these overshoots to learn the size distribution of millimeter and centimeter sized particles.
- Publication:
-
EPSC-DPS Joint Meeting 2011
- Pub Date:
- October 2011
- Bibcode:
- 2011epsc.conf.1307H