Astrometry of the irregular satellites of Jupiter, Saturn, and Uranus
Abstract
"Irregulars” are a dynamically diverse population of satellites that reside in distant orbits around the gas giants of the Solar system. Their orbits frequently have large inclinations, eccentricities, and long periods that may take decades to complete. Currently there are 82 recognized and 20 provisional irregular satellites. The latter are those for which there are insufficient observations to produce well determined orbits. In fact some of the orbits are so poorly known that the satellites are for all practical purposes lost.
Our goal was to develop a method that gives a robust estimate of the orbital uncertainties. We mapped the covariances of our current orbital models over duration of one, three, and ten orbital periods for each of the known irregulars. This progressively longer mapping gives an idea of error growth. We used this measure of the orbital uncertainty to guide our observational strategy in recovery of the irregular satellites of Jupiter, Saturn and Uranus. Our primary recovery platform was the Palomar Hale 5-meter used with the Large-Format Camera (LFC). The LFC has a cross-shaped field of view with a maximum east-west or north-south extent of 24 arcminutes. With a median seeing of about 1.3 arcseconds, the Hale is able to reach visual magnitude 24 in 5 minutes of exposure time. This allowed us to obtain astrometry on some very faint satellites (e.g. Uranian irregulars Margaret and Ferdinand are both fainter that the visual magnitude 25) as well as on many brighter irregulars that were also in the LFC's field of view. We present a summary of our estimated orbital uncertainties and how they compare to the measured positions of the satellites. We also highlight irregular satellites that would benefit from the future observations.- Publication:
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AAS/Division of Dynamical Astronomy Meeting #42
- Pub Date:
- April 2011
- Bibcode:
- 2011DDA....42.1002B