Physics – Geophysics
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000dps....32.4802n&link_type=abstract
American Astronomical Society, DPS Meeting #32, #48.02; Bulletin of the American Astronomical Society, Vol. 32, p.1086
Physics
Geophysics
Scientific paper
In October 1999 we obtained the first radar images of Saturn's rings, using the Arecibo telescope operating at a wavelength of 12.6 cm. The opening angle of the rings, B, was -19.9o, and dual-circular polarization data were collected over a period of 5 days, at ~22 min of receive time per day. We used a frequency-stepped technique similar to that used by Ostro et al. [Icarus, 49, 367 (1982)]. A train of sixteen 100 msec pulses was transmitted every 2.2 sec, an interval slightly longer than the delay depth of the rings, providing a range resolution of 15,000 km. The return echoes were processed to a frequency resolution of about 2 kHz, corresponding to a spatial resolution at the ring ansae of ~2000 km. In order to avoid return pulse overlap, the transmitter frequency was stepped by 800 kHz between pulses. Our observations yield a circular polarization ratio, μ C = 0.70 in the A ring and 0.78 in the B ring, intermediate between values obtained in the 1970s at B=-24.4o and -11.7o [Ostro & Pettengill IAU Colloq. No. 75 (1984)]. In agreement with earlier results [Ostro et al. (1982)], we find no detectable echo from the C ring. At the 3σ level, we can set an upper limit of 0.06 on the ratio of its radar cross-section to that of the B Ring. The most striking feature of the new images is a very pronounced quadrupole azimuthal asymmetry in the brightness of the A Ring, seen in both circular polarizations, which is reminiscent of that seen in ground-based and Voyager images and more recently in HST images [French et al., BAAS 32, 864 (2000)]. By generating synthetic delay-Doppler images of the individual ring components and subtracting these piecewise from the Arecibo images, we find that the azimuthal asymmetry is concentrated in the A Ring, as in visible images, though there is also a suggestion of a much weaker asymmetry in the B ring. Fits of a dynamical model of gravitational wakes [Salo & Karjalainen BAAS 31, 1160 (1999)] to the data show that the asymmetry in the radar maps is over three times that measured in HST images obtained at 439 nm and the same opening angle. This work was supported by NASA's Planetary Geology & Geophysics Program.
Black Gregory J.
Campbell Don B.
French Richard G.
Margot Jean-Luc
Nicholson Philip D.
No associations
LandOfFree
Radar images of Saturn's rings does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Radar images of Saturn's rings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radar images of Saturn's rings will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-867302