Orbital elements for the five irregular Uranian satellites
Following are my current "best orbits" for all five known irregular Uranians. They are based on all astrometry available to me as of July 2001.
Orbits at a glance:
Incl Node Peri ecc a P H dia* Arc
(deg) (deg) (deg) (AU) (yrs) (mag) (km)
S/1997 U 1 139.7 175.0 339.1 .081 .048 1.59 8.8 Jun 1984-Jul 2001
S/1997 U 2 152.6 255.7 17.1 .512 .082 3.53 7.1 Jun 1984-Jul 2001
S/1999 U 1 146.3 249.8 3.4 .562 .116 6.01 10.0 Jul 1999-Jul 2001
S/1999 U 2 141.5 189.4 28.8 .145 .053 1.85 10.9 Jul 1999-Jul 2001
S/1999 U 3 146.3 320.1 170.6 .324 .109 5.47 10.1 Jul 1999-Jul 2001
Incl Node Peri ecc a P H dia Arc
* Still working on these...
Diagram showing the orbits of the Uranian satellites:
As shown in the above perspective view of the orbits, S/1997 U 1 = Caliban = U XVI (green) has almost exactly the same orbit as S/1999 U 2 = Stephano = U XX (magenta). S/1997 U 2 = Sycorax (light blue) and S/1999 U 1 (Setebos) have very similar orbital planes, though the orbit of Sycorax fits well inside that of Setebos. The inclinations of all five satellite are very similar (from 141 to 153 degrees). So far, at least, Uranus appears to have only one family, of retrograde irregular satellites. This is quite different from Jupiter and Saturn, which have retrograde and prograde irregular satellites.
Elements for S/1997 U 1 = Caliban = U XVI: Orbital elements: S/1997 U 1 = Caliban = U XVI Periuranus 1998 Apr 19.312862 TT Epoch 1997 Nov 28.0 TT = JDT 2450780.5 M 271.61767 (2000.0) P Q n 0.62104241 Peri. 339.07160 -0.95424254 -0.29365021 a 0.0479081 Node 174.99098 -0.08220322 0.43921417 e 0.0807123 Incl. 139.68829 -0.28751311 0.84903501 P 1.59 H 8.6 G 0.15 q 0.0440414 From 24 observations 1984 Jun. 1-2001 Jul. 24; RMS error 0.599 arcseconds
Elements for S/1997 U 2 = Sycorax = U XVII: Orbital elements: S/1997 U 2 = Sycorax = U XVII Periuranus 2000 Dec 17.364142 TT Epoch 2000 Sep 13.0 TT = JDT 2451800.5 M 333.36851 (2000.0) P Q n 0.27926095 Peri. 17.08324 -0.48539537 -0.75207452 a 0.0816238 Node 255.93342 -0.84623436 0.27598233 e 0.5117092 Incl. 152.63712 -0.21972419 0.59851287 P 3.53 H 7.2 G 0.15 q 0.0398562 From 46 observations 1984 Jun. 1-2001 Jul. 24; RMS error 0.814 arcseconds
Elements for S/1999 U 1 = Setebos = U XIX: Orbital elements: S/1999 U 1 = Setebos = U XIX Periuranus 2003 Feb 9.198048 TT Epoch 2000 Jul 15.0 TT = JDT 2451740.5 M 205.99742 (2000.0) P Q n 0.16397242 Peri. 3.38736 -0.39092260 -0.75936278 a 0.1164063 Node 249.79550 -0.85696396 0.09408173 e 0.5621304 Incl. 146.34113 -0.33584562 0.64382978 P 6.01 H 10.0 G 0.15 q 0.0509708 From 33 observations 1999 Jul. 18-2001 Jul. 24; RMS error 0.570 arcseconds
Elements for S/1999 U 2 = Stephano = U XX: Orbital elements: S/1999 U 2 = Stephano = U XX Periuranus 1998 Sep 8.060260 TT Epoch 1999 Aug 10.0 TT = JDT 2451400.5 M 178.56657 (2000.0) P Q n 0.53154348 Peri. 28.80253 -0.92605876 0.36349799 a 0.0531452 Node 189.38238 0.09118222 0.47628803 e 0.1447699 Incl. 141.53234 0.36619799 0.80063656 P 1.85 H 10.9 G 0.15 q 0.0454514 From 29 observations 1999 Jul. 18-2001 Jul. 24; RMS error 0.520 arcseconds
Elements for S/1999 U 3 = Prospero = U XVIII: Orbital elements: S/1999 U 3 = Prospero = U XVIII Periuranus 2001 Sep 9.820565 TT Epoch 2000 Jun 25.0 TT = JDT 2451720.5 M 280.43742 (2000.0) P Q n 0.18007894 Peri. 170.56106 -0.84418788 0.40091505 a 0.1093574 Node 320.08612 0.44850724 0.89181310 e 0.3240699 Incl. 146.31924 0.29357802 -0.20961037 P 5.47 H 10.1 G 0.15 q 0.0739180 From 29 observations 1999 Jul. 18-2001 Jul. 24; RMS error 0.385 arcseconds