Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.

Science 31 January 1986:
Vol. 231. no. 4737, pp. 480 - 483
DOI: 10.1126/science.231.4737.480
Prev | Table of Contents | Next

Articles

What Perturbs the ggrdgr Rings of Uranus?

R. G. FRENCH 1, J. A. KANGAS 2, and J. L. ELLIOT 3

1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge 02139.
2 Department of Physics, Massachusetts Institute of Technology, Cambridge 02139.
3 Department of Earth, Atmospheric, and Planetary Sciences and Department of Physics, Massachusetts Institute of Technology, Cambridge 02139.

The ggr and dgr rings have by far the largest radial perturbations of any of the nine known Uranian rings. These two rings deviate from Keplerian orbits, having typical root-mean-square residuals of about 3 kilometers (compared to a few hundred meters for the other seven known rings). Possible causes for the perturbations include nearby shepherd satellites and Lindblad resonances. If shepherd satellites are responsible, they could be as large as several tens of kilometers in diameter. The perturbation patterns of the ggr and dgr rings have been examined for evidence of Lindblad resonances of azimuthal wave number m = 0, 1, 2, 3, and 4. The beta ring radial residuals are well matched by a 2:1 Lindblad resonance. If this represents a real physical phenomenon and is not an artifact of undersampling, then the most plausible interpretation is that there is an undiscovered satellite orbiting 76,522 ± 8 kilometers from Uranus, with an orbital period of 15.3595 ± 0.0001 hours and a radius of 75 to 100 kilometers. Such a satellite would be easily detected by the Voyager spacecraft when it encounters Uranus. The 2:1 resonance location is 41 ± 9 kilometers inside the dgr ring, which makes it unlikely that the resonance is due to a viscous instability within the ring. In contrast, no low-order Lindblad resonance matches the ggr ring perturbations, which are probably caused by one or more shepherd satellites large enough to be clearly visible in Voyager images.

Submitted on November 20, 1985
Accepted on December 26, 1985


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Voyager Finds Uranian Shepherds and a Well-Behaved Flock of Rings: Voyager 2 discovered the moonlets predicted to shape the Uranian rings, two new rings, a predominance of boulders in the rings, and much more.
R. A. Kerr and R. A. KERR (1986)
Science 231, 793-796
   PDF »


To Advertise     Find Products

Science. ISSN 0036-8075 (print), 1095-9203 (online)