The discovery of two irregular Uranian satellites

Details The discovery of two irregular Uranian satellites The discovery of two irregular Uranian satellites

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998dda....30.1201n&link_type=abstract

American Astronomical Society, DDA meeting #30, #12.01; Bulletin of the American Astronomical Society, Vol. 30, p.1147

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Scientific paper

In September 1997 two small outer satellites of Uranus, provisionally designated S/1997 U 1 and S/1997 U 2, were discovered with the Palomar 5m Hale telescope (IAUC 6764, 6765). With R magnitudes of 21.9 and 20.4, respectively, these bodies are the first known irregular Uranian satellites. Like the 10 previously known irregular moons of Jupiter, Saturn and Neptune, U1 and U2 occupy relatively distant (200--350 planetary radii), eccentric and inclined orbits. Based on their observed magnitudes and an assumed albedo of 0.07, their radii are ~ 30 and 60 km, respectively. While the newly found objects seem to be dynamically akin to other irregulars, their B-R and R-I colors of ~ 1.6 and ~ 0.6 are much redder than those of either the other irregular moons or the inner Uranian satellites, and are more similar to those measured for TNOs and Centaurs. The table gives estimated orbital elements (J2000) based on observations in Sept and Oct 1997 (IAUC 6765); additional observations through Nov 29 (IAUC 6780); and fits including solar and planetary perturbations (orbits 2 & 3). Orbit 3 also fits two tentatively identified pre-discovery images of U2 from plates obtained in June 1984 by D. Cruikshank. Parenthetical values were assumed. The large inclinations imply that both satellites must exhibit strong secular (Kozai effect) oscillations induced by solar perturbations, with amplitudes of 10--20% in e and sin i on time scales of 2,000--5,000 yr. \begin{tabular}{lcccccc} & \multicolumn{3}{c}S/1997 U 1 & \multicolumn{3}{c}S/1997 U 2 & 6765 & 6780 & orbit 2 & 6765 & 6780 & orbit 3 a/R_U & (224.5) & 304.2 & 276.2 & 224.5 & 252.7 & 346.1 e & 0.160 & (0.2) & 0.044 & 0.521 & (0.4) & 0.345 i & 137.8 & 146.4 & 140.9 & 149.4 & 153.5 & 154.5 omega & 13.2 & 141.9 & 17.2 & 232.9 & 256.2 & 341.1 Omega & 182.3 & 185.8 & 177.6 & 210.6 & 221.2 & 244.7 T & 97/2/08 & 97/6/27 & 96/12/01 & 98/4/03 & 97/2/10 & 97/4/26 P (d) & (415) & 654 & 567 & 415 & 495 & 795

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