Discovering three new moons in our solar system

Thanks to new observations made with various telescopes, Uranus is now much richer than the Moon. And Neptune gets two more!

These are absolutely amazing discoveries. For example, a new moon was discovered around Uranus for the first time in 20 years. One of the new moons spotted around Neptune will fall as the weakest moon yet discovered by ground-based telescopes.

Uranus
The diameter of the Moon around Uranus is only 8 km. This makes it likely the smallest moon the ice giant has. The Moon takes 680 days to complete an orbit around Uranus. For now, the moon is referred to as S/2023 U1, but it will be given an official name soon. It is still unclear what this means. But the moon would almost certainly be named after a character from a play by Shakespeare or Alexander Pope; Other moons of Uranus are also named after characters created by Shakespeare and Pope.

Neptune
Neptune is also richer with two moons. One moon is about 23 kilometers in diameter and takes 9 years to complete an orbit around Neptune. This moon is provisionally referred to as S/2002 N5. The second moon is much smaller and has a diameter of 14 kilometers. This moon – called S/2021 N1 – is also very faint and takes nearly 27 years to complete an orbit around Neptune. These two moons will also receive an official name at a later stage – similar to the previously discovered moons of Neptune – and will be named after sea nymphs from Greek mythology.

Notes
The discovery of the three moons was preceded by many observations and research. For example, Neptune's two moons were first observed in September 2021. However, follow-up observations using the Magellan telescopes in Chile – in 2021, 2022 and 2023 – were needed to confirm that the brighter star – S/2002 N5 – was indeed orbiting Neptune. To confirm the existence of the fainter S/2021 N1, subsequent observations from the Very Large Telescope in Chile and the Gemini Observatory in Hawaii were necessary.

Uranus' moon S/2023 U1 was first spotted in November last year. Subsequent observations in December allowed researchers to sharpen the moon's orbit. With this information, they were then able to observe the moon in images taken in 2021 from the Magellan telescopes in Chile and the Subaru telescope in Hawaii.

Panlimentin
All three moons now discovered around Neptune and Uranus orbit their planet at a great distance. Their orbits are also inclined and eccentric (not perfectly circular). This suggests that the ice giants' gravity took over shortly after the birth of Uranus and Neptune, the researchers said.

Agreements
What is also striking is that both Uranus and Neptune have moons that contain orbital elements similar to the moons now discovered. For example, S/2023 U1 has an orbit similar to that of Uranus' moons Caliban and Stefano. While S/2021 N1 has an orbit similar to that of Neptune's Psamathi and Nisu. Meanwhile, S/2002 N4 once again has an orbit very similar to that of Neptune's moons Sao and Laomidia. This is no coincidence. This suggests that these moons were once part of a larger celestial body that broke up at some point, perhaps due to collisions with other celestial bodies. Its fragments then continued to revolve around Uranus and Neptune in similar orbits. Thus, these groups of moons clearly attest to the fact that the early solar system was a rather chaotic place where different objects were constantly moving and colliding with each other.

Young solar system
The latter also immediately demonstrates why the discovery of these three moons is so interesting; They give us more knowledge about conditions in the young solar system. Researchers hope to learn more about these moons – and thus also about the early years of our solar system – during future missions to Neptune and Uranus.

With the discovery of the new moons, the total number of moons around Uranus reaches 28. Neptune – including the new discoveries – will now have 16 moons. Is there more to discover there? Without a doubt! The researchers expect that they have identified all moons with a diameter of 14 kilometers or larger around Neptune, while all moons with a diameter of 8 kilometers or larger have been discovered around Uranus. Smaller specimens are harder to see and undoubtedly still waiting to be discovered.