Everyone knows that the Earth only has one moon orbiting the planet. We all get to see it most nights, no matter where we are on the globe. While Earth has only one moon, other planets have significantly more. Jupiter for instance, has 79 known moons and may have one more.
Last year, an amateur astronomer recovered four lost Jovian moons and, during the process, discovered a previously unknown moon. The amateur astronomer is Kai Ly, and the discovery was a spinoff of the earlier investigation of pre-recovery images of recently discovered moons of Jupiter, including Valetudo, Ersa, and Pandia. The moons were discovered while examining data taken in 2003 using the 3.6-meter Canada-France-Hawaii Telescope.
Those images had previously been used to discover 33 new moons orbiting Jupiter. Those images remain online, and Ly thought there could be more undiscovered moons hiding in the data gathered in 2003. Ly began by examining images taken in February 2003 when Jupiter was at opposition, and its moons were at their brightest.
Examinations of three survey images covering the same region of sky at different times of the night of February 24 resulted in the discovery of three potential moons moving at 13 to 21 arcseconds per hour. Ly was unable to recover two of the potential moons on other nights but did find the third. It has been temporarily designated EJC0061 on survey observations from February 25-27 and on images taken via the Subaru Telescope on February 5 and 6.
Those images suggested a 22-date arc indicating the object was bound to Jupiter. Ly had enough data to trace the moon’s orbit on survey images from March 12 to April 30. The moon was found near its predicted position, and later images taken by telescopes on observations taken through early 2018. The moon is very faint, ranging in magnitude from 23.2 to 23.5. Ultimately, the study gathered an arc of 76 observations over slightly more than 15 years giving enough data to consider its orbit well-secured for decades.