Irregular moons of Saturn -- Phoebe For notes, see https://tilmanndenk.de/outersaturnianmoons/phoebe/#1 31 Jul 2019 / TD Overview Table Moon name Phoebe Saturn range 13e6 km Orbit period 1.5 years Orbit direction retrograde Size ~ 213 km Rotation period 9 16 hh:mm Discovery year 1899 (A) Designations and discovery circumstances (A1) Moon name Phoebe (A2) Moon abbrev. (TD) Pho (A3) IAU number Saturn IX (A4) Provisional designation -- (A5) SPICE ID 609 (A6) Also-used label S09 (A7) First observation date 16 Aug 1898 (A7) Announcement date 17 Mar 1899 (A7) Harvard Obs. Bull. announcement no. 49 (A8) Discoverers Pickering, W.H., Stewart, D. (B) Orbit parameters (B1) Orbit direction retrograde (B2) Group member Norse (B3) Dynamical family ? (B4) Periapsis range 10.83e6 km (B5) Semi-major axis 12.948e6 km (B6) Apoapsis range 15.06e6 km (B7) Semi-major axis 215 R_Saturn (B8) Semi-major axis 0.087 au (B9) Semi-major axis 0.20 R_Hill (B10) Orbit eccentricity 0.163 (B11) Orbit inclination 175.24 ° (B12) Inclination supplemental angle 4.76 ° (B13) Orbital period 548 d (B14) Orbital period 1 6 0 y:m:w (B15) Mean orbit velocity 1.71 km/s (C) Physical parameters (C1) Mean size ~ 213 -1 +1 km (C2) Mean radius ~ 106.4 km (C3) Equatorial circumference ~ 685 km (C4) Minimum equatorial axes ratio 1.01 (C5) Axes radii (a x b x c) ~ 109 108 102 km (C5) (C6) Mass ~ 8.29e18 kg (C7) Mean density (?) 1.64 g/cm^3 (C8) Surface escape velocity ~ 320 km/h (C9) Rotation period (sidereal) 9.273651 h (C9) Rotation period error 0.000006 h (C9) Spin rate 2.588 d^(-1) (C10) Spin direction prograde (C11) Seasons none (C12) Pole direction (ecliptic longitude λ) 61.2 ±0.3 ° (C12) Pole direction (ecliptic latitude β) 64.46 ±0.1 ° (C13) Pole direction (geocentric RA) 356.6 ±0.3 ° (C13) Pole direction (geocentric Dec) +78.0 ±0.1 ° (C14) Absolute visual magnitude ~ 6.6 mag (C15) Apparent visual magnitude from Earth 16 mag (C16) Best apparent magnitude for Cassini 5.1 mag (C17) Spectral slope ~ -2.5 %/100nm (C17) B-R color index ~ 0.98 0.91 (C18) Albedo (?) 0.06 (C19) Hill sphere radius ~ 18000 km (C20) Hill sphere radius ~ 170 r_Pho