Reports

1979J2: The Discovery of a Previously Unknown Jovian Satellite

Science  14 Nov 1980:
Vol. 210, Issue 4471, pp. 786-788
DOI: 10.1126/science.210.4471.786

Abstract

During a detailed examination of imaging data taken by the Voyager 1 spacecraft within 4.5 hours of its closest approach to Jupiter, a shadow-like image was observed on the bright disk of the planet in two consecutive wide-angle frames. Analysis of the motion of the image on the Jovian disk proved that it was not an atmospheric feature, showed that it could not have been a shadow of any satellite known at the time, and allowed prediction of its reappearance in other Voyager 1 frames. The satellite subsequently has been observed in transit in both Voyager 1 and Voyager 2 frames; its period is 16 hours 11 minutes 21.25 seconds ± 0.5 second and its semimajor axis is 3.1054 Jupiter radii (Jupiter radius = 7.14 x 104 kilometers). The profile observed when the satellite is in transit is roughly circular with a diameter of 80 kilometers. It appears to have an albedo of0.05, similar to Amalthea's.