Astronomers have discovered three new satellites of the planets Uranus and Neptune

Astronomers have discovered three previously unknown satellites around Uranus and Neptune, the most distant planets in our solar system.

This image shows the new Uranian moon S/2023 U1 using the Magellan telescope

The discovery includes a moon spotted in the orbit of Uranus, the first such discovery in more than 20 years, and two detected in the orbit of Neptune, writes

“The three newly discovered satellites are the faintest ever found around these two ice giant planets using ground-based telescopes,”
said Scott S. Sheppard, an astronomer at the Carnegie Institution for Science, in a statement. “It took special image processing to reveal such faint objects.”

The revelations will be useful for missions that may be planned to more closely explore Uranus and Neptune in the future, a priority for astronomers since the icy planets were only observed in detail with Voyager 2 in the 1980s.

The three moons were announced on February 23 by the International Astronomical Union's Center for Minor Planets.

Finding faint satellites

The newly discovered Uranian moon is the 28th moon observed orbiting the ice giant, and is also likely the smallest, measuring 8 kilometers in diameter. The moon, called S/2023 U1, takes 680 Earth days to orbit the planet. In the future, the small satellite will be named after a Shakespearean character, in keeping with the tradition of Uranus' moons bearing literary names.

Sheppard spotted the Uranian moon in November and December while making observations with the Magellan telescopes at the Las Campanas Observatory in Chile. He collaborated with Marina Brozovic and Bob Jacobson of NASA's Jet Propulsion Laboratory in Pasadena, California, to determine the moon's orbit.

The Magellan telescopes also played a key role in Sheppard's discovery of the brighter of the two new Neptunian moons, S/2002 N5. The Subaru Telescope, located on Hawaii's dormant Mauna Kea volcano, helped Sheppard and his collaborators, astronomer David Tholen of the University of Hawaii, astronomer Chad Trujillo of Northern Arizona University and planetary scientist Patryk Sofia Lykawka of Kindai University in Japan , to focus on the other extremely faint Neptunian moon, S/2021 N1.

Both moons, which bring the total number of known natural satellites of Neptune to 18, were first observed in September 2021, but required follow-up observations with different telescopes over the past two years to confirm their orbits.

“Once S/2002 N5's orbit around Neptune was determined using observations from 2021, 2022 and 2023, it was traced back to an object that was spotted near Neptune in 2003 but was lost before it can be confirmed to be orbiting the planet,” Sheppard stated.

The bright moon S/2002 N5 is 23 kilometers (14 miles) in diameter and takes nearly nine years to complete an orbit around Neptune, while the faint moon S/2021 N1 is 14 kilometers ( 8.7 miles) and has a long orbit of about 27 years. Both would eventually be given new names referencing the Nereid sea goddesses of Greek mythology. Neptune was named after the Roman god of the sea, so the planet's moons are named after lesser sea gods and nymphs.

Finding all three moons required dozens of short, five-minute exposures over the course of three or four hours on different nights.

Because the moons move in only a few minutes relative to the stars and galaxies in the background, single long exposures are not ideal for capturing deep images of moving objects.” Sheppard stated. “By overlaying these multiple exposures, stars and galaxies appear streaked behind them, and moving objects similar to the host planet will be seen as point sources, removing the moons from behind the background noise in the images.”

A chaotic solar system

By studying the distant and angular orbits of the satellites, Sheppard hypothesized that the satellites were drawn into the orbits of Uranus and Neptune by the gravitational influence of the giant planets shortly after they formed. The outer moons orbiting all the giant planets in our solar system—Jupiter, Saturn, Uranus, and Neptune—have similar configurations.

Even Uranus, which is tilted on its side, has a lunar population similar to that of the other giant planets orbiting our Sun,”
Sheppard stated. “And Neptune, which likely captured the distant Kuiper Belt object Triton — an ice-rich body larger than Pluto — an event that could have disrupted its moon system, has outer moons that look similar to those of its neighbors .”

It is possible that some of the satellites around the giant planets are fragments of once larger satellites that collided with asteroids or comets and broke apart.

Understanding how giant planets captured their satellites is helping astronomers reconstruct the chaotic beginnings of our solar system.