How many moons does Jupiter have?
15 June 2017:
Two new moons were announced on 2 June 2017, and 5 June 2017. These moons, provisionally named S/2016 J 1 and S/2017 J 1, were discovered on 8 March 2016 and 23 March 2017, respectively. The announcements only came out this month because the International Astronomical Union insists on confirmation that a new body actually exists, by other astronomers, before going public. It took so long to verify their existence because these moons are absolutely tiny, at probably no more than 2km across. Incidentally, astronomers have actually lost some of the earlier moons. They’re tiny, so they’re easily buffeted by the gravity of other passing objects, and they’re hard to see so we don’t always spot when that happens!
18 July 2018
A group of astronomers searching for a 9th planet, predicted to have a highly elliptical orbit way out beyond that of Pluto, happened to have Jupiter drift through the area of sky they were studying. They didn’t find the elusive world, but did stumble upon a batch of new moons orbiting Jupiter, bringing the total up to 79.
13 February 2023
After the last update to this page, it started to seem a bit silly to keep counting. New discoveries were coming in all the time, old discoveries were starting to get disputed, and we had more interesting topics to follow. Until a few days ago when we saw the most recent discovery announcement, bringing the count up to 92 moons! However… some of these moons are so tiny that not everybody agrees that they’re all really there. Some have been seen once, but not seen since. So for now, the official number is actually a range: “Between 80 and 92”. So that’s where we’ll leave it till the next update!