Jupiter now has 69 known moons with the addition of S/2016 J1 and S/2017 J1 announced in early June of 2017.
Discovery of the New Moons:
We have been continuing our survey looking for very distant objects in the outer solar system beyond Pluto and the Kuiper Belt, which includes looking for new planets such as Planet X in the very outer fringes of our Solar System. Jupiter just happened to be in the area we were looking at in March of 2016 and 2017. We imaged several fields that were very close to Jupiter, whiched allowed us to look for Jupiter moons in the foreground while at the same time look for very distance objects that were well beyond Jupiter in the background. During these observing campaigns we found most of the known moons of Jupiter as well as several that were not known or were lost.
There are several lost moons of Jupiter that were discovered in 2003. They are known moons, but their orbits are not well enough known to accurately predict where they are now, so they are considered lost. There were 14 of these lost moons at the beginning of 2016. We have for sure recovered five of the lost moons as our observations for five of our new Jupiter moon discoveries were able to easily link back to the lost moons by linking our one year of observations in 2016 and 2017 with the 2003 lost moons. We likely have all of the lost moons in our new observations from 2017, but to link them back to the remaining lost 2003 objects requires more observations a year later to confirm the linkages, which will not happen until early 2018.
S/2016 J1 and S/2017 J1 are new moons we first observed in March 2016 and March 2017, respectively. We confirmed they were not lost moons with having over one year of observations on both, giving us 2 new Jupiter moons and making 69 known moons of Jupiter. There are likely a few more new moons as well in our 2017 observations, but we need to reobserve them in 2018 to determine which of the discoveries are new and which are lost 2003 moons. Stay Tuned.
Figure 1:Movies of two newly discovered Jupiter moons (Left S/2016 J1; Right S/2017 J1) showing their motion relative to background stars and galaxies. Click on the images to learn more about them.
Here is a table and diagram showing all of Jupiter's known satellites .
To learn more about the satellites of Jupiter and other planets visit The Jupiter Moon Page.
Scott S. Sheppard