Mosaic of Jupiter made from Cassini images acquired on Dec. 29, 2000 (NASA/JPL-Caltech/SSI)
Jupiter has long been known to have the most moons of all the planets in the Solar System—just barely surpassing Saturn’s official 62, although that’s not taking into consideration the larger chunks of icy material within Saturn’s rings—and its leading margin has just increased even further with the discovery of two more moons, bringing Jupiter’s tally up to 69.
The new moons were identified by a small team of astronomers while searching the sky for evidence of the hypothesized “Planet Nine” far beyond Pluto. Currently named S/2016 J 1 and S/2017 J 1, the new moons are only about a mile across and are in highly-inclined, retrograde orbits around Jupiter—that is, in the opposite direction of the planet’s rotation. This implies that they are likely captured objects rather than having formed around the planet itself (which is actually a common feature among smaller Jovian moons.)
Read the rest of this news from Kelly Beatty at Sky and Telescope here: Two New Satellites for Jupiter