Radio occultation of Saturn's rings with the Cassini spacecraft : ring microstructure inferred from near-forward radio wave scattering
Abstract/Contents
- Abstract
- The Cassini spacecraft is a robotic probe sent from Earth to orbit and explore the planet Saturn, its moons, and its expansive ring system. Between May 3 and August 2 of 2005, we undertook a series of radio occultation experiments, during which the Cassini spacecraft operated in conjunction with the NASA Deep Space Network (DSN) to probe the rings at three distinct radio wavelengths. During our occultation experiments, Cassini flies behind the rings of Saturn as viewed from Earth and transmits coherent radio signals at wavelengths of 13 cm, 3.6 cm, and 0.94 cm, in the radio bands known as S, X, and Ka, respectively. These signals pass through the rings and are received and recorded on Earth at the large antenna complexes of the DSN. At each of the three transmitted frequency channels, the received signal comprises two components, i) a direct (coherent) component, which is the transmitted sinusoid, attenuated and phase shifted by the average effect of its interaction with the interceding ring material, and ii) a scattered (incoherent) signal component, comprising energy that is forward-scattered towards the receiver from all of the ring particles illuminated by the transmitting antenna's beam. The time- and spatially-averaged diffraction signature of ring microstructure---which forms when individual ring particles organize into large clusters or groups under the influence of collisional and self-gravitational forces---is superimposed on the scattered signal. Coherent radio waves transmitted by the Cassini spacecraft are diffracted at various locations in Ring A and B and indicate the presence of fine-scale structure showing periodic variation in optical depth, which we refer to as periodic microstructure (PM). We interpret the observed spectral signature using simple diffraction grating models, yielding estimates of the structural period that range between 100 and 250 meters. In all regions, the structure appears to be approximately symmetric in azimuth. Prior to Cassini, axisymmetric periodic microstructure was predicted by fluid dynamical theory and by the results of dynamical simulations of the rings, but was not observed experimentally. Our observations are among the first to directly observe PM in the rings, and to report estimates of its structural period and orientation in five distinct regions across Rings A and B.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2010 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Thomson, Fraser Stuart |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering |
| Primary advisor | Marouf, Essam |
| Primary advisor | Zebker, Howard A |
| Thesis advisor | Marouf, Essam |
| Thesis advisor | Zebker, Howard A |
| Thesis advisor | Enge, Per |
| Advisor | Enge, Per |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Fraser Stuart Thomson. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2010. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2010 by Fraser Stuart Thomson
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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