Lunar occultation of Saturn III. How big is Iapetus?
Abstract
By considering both the orbital lightcurve of Iapetus and data obtained during the March 30, 1974, occultation of the satellite by the Moon, we obtain information about the brightness distribution on the bright face of Iapetus and derive an accurate value for the satellite's radius. From the observed orbital lightcurve we find that the trailing face of Iapetus must consist predominantly of a single bright material with an effective limb-darkening parameter of k = 0.62 -0.120.10. Given this result the occultation observations imply a radius of 718 -78+87 km. If the patchy albedo model proposed by Morrison et al. represents the surface of Iapetus accurately (as far as the relative albedo distribution is concerned) then the radius of Iapetus is 724 ± 60 km. Both estimates are consistent with the radiometric radius of 835 (+50, -75) km derived by Morrison et al. Combining our results with the value of 0.60 ± 0.14 for the normal reflectance (in V) of the material at the center of the bright face derived by Elliot et al. we find that the normal reflectance of the dark side material is 0.11 -0.03+0.04. These values are higher than the corresponding values of 0.35 and 0.05 quoted by Morrison et al.
- Publication:
-
Icarus
- Pub Date:
- February 1978
- DOI:
- 10.1016/0019-1035(78)90149-5
- Bibcode:
- 1978Icar...33..301V
- Keywords:
-
- Astrometry;
- Iapetus;
- Light Curve;
- Lunar Occultation;
- Size Determination;
- Albedo;
- Astronomical Models;
- Brightness;
- Limb Darkening;
- Reflectance;
- Saturn (Planet);
- RADIUS;
- SURFACE;
- MOON;
- OCCULTATIONS;
- ALBEDO;
- IAPETUS;
- ORBITS;
- LIMBS;
- SATURN;
- BRIGHTNESS;
- LIGHT CURVE;
- Lunar and Planetary Exploration; Saturn; Satellites of Saturn, Earth Science