With over 70 officially recognized moons, Jupiter is a giant planet well surrounded. However, this does not prevent astronomers from continuing to discover them, including amateur astronomers. Indeed, the amateur astronomer who found four lost Jovian moons last year became the first amateur to discover a hitherto unknown natural satellite. Kai Ly reported the find to the Minor Planet Mailing List on June 30 and submitted it for publication as Minor Planet Electronic Circular.
Ly’s quest was a continuation of earlier identification of images of recently discovered Jovian moons, including Valetudo, Ersa, and Pandia, when examining data taken in 2003 with the Canada-France-Hawaii Telescope (CFHT) from 3.6 meters. David Jewitt and Scott Sheppard (University of Hawaii) had led a group that used these images to discover 23 new moons. The images remained available online, and Ly thought more undiscovered moons might be lurking in the 2003 data set.
A patient and meticulous hunt
After planning his research in May, Ly began in early June to examine images taken in February 2003, when Jupiter was in opposition and its moons were the brightest. Astronomers examined three images covering the same region of the sky at different times on the night of February 24 and found three potential natural satellites moving at 13 to 21 arc seconds per hour overnight. Ly was unable to track down two of the potential moons on other nights, but found the third, temporarily designated EJc0061, on sightings February 25-27 and images taken with the Subaru telescope on February 5-6. This established a 22 arc day, which suggested that the object was related to Jupiter.
Ly therefore had enough information to trace the orbit of the moon on observational images from March 12 to April 30. ” From there, the quality of the orbit and ephemeris was decent enough that I could start looking for sightings beyond 2003. », Explains Ly. He and his team found the moon near its predicted position in later images from the Inter-American Observatories of Subaru, CFHT and Cerro Tololo taken through early 2018. The moon ranges in magnitude from 23.2 to 23.5.
The end result was an arc of 76 observations over 15.26 years (5,574 days), enough for Ly to consider his orbit secure for decades. The data is tracking the moon – tentatively designated S / 2003 J 24 pending release – through nearly eight 1.9-year-old Jupiter orbits, says David Tholen (University of Hawaii), more than enough to show it is is a moon. Tholen did not verify the footage, but says the evidence looks strong: “ It would be nearly impossible for the artifacts to adapt to a jovicentric orbit on so many different nights using different cameras. ».
A moon belonging to the Carmelite group
« I am proud to say that this is the first planetary moon discovered by an amateur astronomer! Ly says. But, they admit, ” he is just a typical member of the Retrograde Carmelite group “. This group includes 22 other small moons orbiting Jupiter in the opposite direction of its rotation with periods of approximately two years. Their orbits are similar enough to suggest that they were all fragments of a single impact. They are probably pieces of Carme, the first of the group to be discovered and with 45 kilometers in diameter, by far the largest.
Such little Jovian retrograde moons can be found in even greater numbers. Last year, Edward Ashton, Matthew Beaudoin and Brett J. Gladman (University of British Columbia, Canada) spotted some four dozen objects 800 meters in diameter, which appeared to orbit Jupiter. They didn’t follow them long enough to prove the objects were Jovian moons, but from their preliminary observations they suggested that Jupiter might have some 600 satellites at least 800 meters in diameter. The development of larger, more sensitive telescopes will make room for new discoveries.