3 Previously Unknown Moons Found Circling Neptune and Uranus: First Ever Lunar Discoveries Around These Planets

According to the NASA/JPL Solar System Dynamics Team, there are a total of 290 known moons currently orbiting the planets in our solar system.

The tally includes one moon for Earth, two for Mars, 95 for Jupiter, 146 for Saturn, 27 for Uranus, 14 for Neptune, and five for dwarf planet Pluto. In a recent discovery, it was discovered that the lunar inventory in our celestial neighborhood has increased by three.

New Members of the Solar System

On February 23, the International Astronomical Union's Minor Planet Center announced the discovery of three previously unknown moons, two circling Neptune and one around Uranus. The latest inventory puts Uranus at 28 known moons and Neptune at 16.

The brighter one in Neptune's new moons is temporarily named S/2022 N5. It measures 14 miles (23 kilometers) wide and has an orbital period of 9 years. On the other hand, the fainter satellite is assigned the name S/2021 N1. Measuring 8.6 miles (14 kilometers) wide and has the longest known orbital journey of 27 years. The two Neptunian moons will be given permanent names which will be taken from sea gods and nymphs in Greek mythology.

Meanwhile, the newly discovered moon that orbits Uranus has an estimated diameter of 5 miles (8 kilometers), possibly the smallest of its group. It also takes 680 days to complete one orbit around the ice giant.

Uranus' new moon is the first detected around the giant planet in over 20 years. According to astronomer Scott S. Sheppard from the Carnegie Institution for Science, they suspect that there are many more smaller moons, although they are yet to be discovered. According to a statement by Carnegie Science, the new moon will be named after a Shakespearean character to keep with the naming conventions for outer Uranian moons. Until then, it will be referred to as S/2023 U1.

How Were the New Moons Discovered?

Sheppard first spotted S/2023 U1 on November 4, 2023 using the Magellan telescopes at Las Campanas Observatory in Chile. After a month, he made follow-up observations at Magellan and worked with Bob Jacobson and Marina Brozovic of NASA's Jet Propulsion Laboratory. After determining a potential moon orbit for the new discovery, Sheppard located the new member of Uranian satellites. This was done by comparing the older images that he took in 2021 at Magellan telescope and at the Subaru telescope in Hawaii.

It was also the Magellan telescope which was used in finding the brighter of the two newly found Neptunian moons. Sheppard collaborated with Patryk Sofia Lykawa of Kindai University, Chad Trujillo of Northern Arizona University, and David Tholen of the University of Hawaii to make it happen. The fainter Neptunian moon, on the other hand, was spotted using the Subaru telescope. Both of the two moons were first detected in September 2021.

Follow-up observations carried out on the Magellan telescope in October 2021, in 2022, and in November 2023 confirmed the brighter moon as orbiting Neptune. For the fainter moon, special observing time was required under the European Southern Observatory' Very Large Telescope and on Gemini Observatory. Ultra-pristine conditions of an 8-meter (26 feet) telescope were needed to secure the moon's orbit.

The discovery of the three of the new moons required taking several five-minute exposures over three- or four-hour periods on a series of nights. The exposures were shifted by the apparent motion of each respective planet and then added together to create a single very deep image.