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NASA/JPL-Caltech/B. Jonsson
NASA’s Voyager 2 spacecraft captured these views of Uranus (left) and Neptune (right) during its flybys of the planets in the 1980s.
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Astronomers have discovered three previously unknown moons around Uranus and Neptune, the most distant planets in our solar system.
The find includes a moon discovered orbiting Uranus (the first discovery of its kind in more than 20 years) and two detected in the orbit of Neptune.
“The three newly discovered moons 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. “Special image processing was needed to reveal such faint objects.”
The revelations will be useful for missions that may be planned to explore Uranus and Neptune more closely in the future, a priority for astronomers since the ice 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 Minor Planet Center.
The newly discovered moon of Uranus is the 28th observed orbiting the ice giant and is also probably the smallest, measuring 8 kilometers (5 miles) in diameter. The moon, called S/2023 U1, takes 680 Earth days to complete one orbit around the planet. In the future, the small satellite will be named after a Shakespeare character, in keeping with the tradition of Uranus’s moons bearing literary names.
Sheppard saw Uranus’s moon in November and December while making observations using the Magellan telescopes at the Las Campanas Observatory in Chile. He worked with Marina Brozovic and Bob Jacobson of NASA’s Jet Propulsion Laboratory in Pasadena, California, to determine the moon’s orbit.
Scott Sheppard/Carnegie Science
This discovery image shows the new moon of Uranus S/2023 U1 using the Magellan Telescope on November 4, 2023. Uranus (top left) is just outside the field of view.
Magellan’s telescopes also played a key role in helping Sheppard find 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, bringing the total of known natural satellites of Neptune to 18, were first detected in September 2021, but required follow-up observations with different telescopes over the past few 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 detected near Neptune in 2003 but was lost before it could be confirmed. orbiting the planet,” Sheppard said. .
The bright moon S/2002 N5 is 14 miles (23 kilometers) in diameter and takes almost nine years to complete one orbit of Neptune, while the faint S/2021 N1 is about 8.7 miles (14 kilometers) in diameter and a long orbit of approximately 27 years. Both will eventually receive new names that reference 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 nymphs and minor sea gods.
Finding the three moons required dozens of short, five-minute exposures over the course of three or four hours on different nights.
“Because moons move in just a few minutes relative to background stars and galaxies, long single exposures are not ideal for capturing deep images of moving objects,” Sheppard said. “By overlaying these multiple exposures, stars and galaxies appear with trails behind them, and moving objects similar to the host planet will be seen as point sources, bringing the moons out from behind the background noise in the images.”
By studying the distant angular orbits of the moons, Sheppard hypothesized that the satellites were drawn into orbit around Uranus and Neptune due to the gravitational influence of the giant planets shortly after their formation. The outer moons orbiting all of our solar system’s giant planets (Jupiter, Saturn, Uranus, and Neptune) share similar configurations.
“Even Uranus, which is tilted on its side, has a lunar population similar to other giant planets orbiting our Sun,” Sheppard said. “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 lunar system, has outer moons that appear similar to their neighbors.”
It is possible that some of the moons around the giant planets are fragments of once larger moons that collided with asteroids or comets and broke up.
Understanding how giant planets captured their moons helps astronomers reconstruct the chaotic early days of our solar system.