Irregular moons of Saturn -- Aegir For notes, see https://tilmanndenk.de/outersaturnianmoons/aegir/#1 22 Oct 2018 / TD Overview Table Moon name Aegir Saturn range 21e6 km Orbit period 3.1 years Orbit direction retrograde Size ~ 5 km Rotation period unknown Discovery year 2004 (A) Designations and discovery circumstances (A1) Moon name Aegir (A2) Moon abbrev. (TD) Aeg (A3) IAU number Saturn XXXVI (A4) Provisional designation S/2004 S 10 (A5) SPICE ID 636 (A6) Also-used label S36 (A7) First observation date 12 Dec 2004 (A7) Announcement date 04 May 2005 (A7) IAU circular announcement no. 8523 (A8) Discoverers Jewitt D. et al. (B) Orbit parameters (B1) Orbit direction retrograde (B2) Group member Norse (B3) Dynamical family Mundilfari (B4) Periapsis range 15.52e6 km (B5) Semi-major axis 20.75e6 km (B6) Apoapsis range 25.98e6 km (B7) Semi-major axis 344 R_Saturn (B8) Semi-major axis 0.139 au (B9) Semi-major axis 0.32 R_Hill (B10) Orbit eccentricity 0.25 (B11) Orbit inclination 166.7 ° (B12) Inclination supplemental angle 13.3 ° (B13) Orbital period 1118 d (B14) Orbital period 3 0 3.25 y:m:w (B15) Mean orbit velocity 1.35 km/s (C) Physical parameters (C1) Mean size ~ 4.5 -0.5 +1.5 km (C2) Mean radius ~ 2.2 km (C3) Equatorial circumference ~ 15 km (C4) Minimum equatorial axes ratio unknown (C5) Axes radii (a x b x c) ~ unknown (C5) (C6) Mass ~ 2.3e13 kg (C7) Mean density (?) 0.5 g/cm^3 (C8) Surface escape velocity ~ 3 km/h (C9) Rotation period unknown (C9) Rotation period error - (C9) Spin rate unknown (C10) Spin direction unknown (C11) Seasons unknown (C12) Pole direction (ecliptic longitude λ) unknown (C12) Pole direction (ecliptic latitude β) unknown (C13) Pole direction (geocentric RA) unknown (C13) Pole direction (geocentric Dec) unknown (C14) Absolute visual magnitude ~ 15.5 mag (C15) Apparent visual magnitude from Earth 24.4 mag (C16) Best apparent magnitude for Cassini 15.8 mag (C17) Spectral slope unknown (C17) B-R color index 1.30 (C18) Albedo (?) 0.06 (C19) Hill sphere radius ~ 360 km (C20) Hill sphere radius ~ 165 r_Aeg