The three newly-discovered moons — S/2023 U1, S/2002 N5 and S/2021 N1 — are the faintest ever found around Uranus and Neptune using ground-based telescopes.
Provisionally named S/2023 U1, the new Uranian moon was first spotted on November 4, 2023, by Carnegie Institution for Science astronomer Scott Sheppard using the Magellan telescopes at Las Campanas Observatory.
At only 8 km (5 miles), it is probably the smallest of Uranus’ moons. It takes 680 days to orbit the ice giant.
S/2023 U1 will eventually be named after a character from a Shakespeare play, in keeping with the naming conventions for outer Uranian satellites.
Its discovery brings the ice-giant planet’s total moon count to 28.
Dr. Sheppard also used the Magellan Telescope to find S/2002 N5, the brighter of the two newfound Neptunian moons.
The moon is about 23 km (14.3 miles) in diameter, and takes almost 9 years to orbit the ice giant.
The fainter Neptune moon was discovered in by Dr. Sheppard and his colleagues using the Subaru telescope.
Named S/2021 N1, it is about 14 km (8.7 miles) accross, and has an orbital period of almost 27 years.
Both S/2002 N5 and S/2021 N1 were first seen in September 2021.
They will both receive permanent names based on the 50 Nereid sea goddesses in Greek mythology.
“Once S/2002 N5’s orbit around Neptune was determined using the 2021, 2022, and 2023 observations, it was traced back to an object that was spotted near Neptune in 2003 but lost before it could be confirmed as orbiting the planet,” Dr. Sheppard said.
S/2023 U1, S/2002 N5 and S/2021 N1 have distant, eccentric, and inclined orbits that suggests they were captured by the gravity of these planets during or shortly after Uranus and Neptune formed from the ring of dust and debris that surrounded our Sun in its infancy.
All of the giant planets in our Solar System have similar configurations for their outer moons, regardless of their size or the process by which they formed.
“Even Uranus, which…
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