Discovery of three new moons orbiting Uranus and Neptune

NASA/JPL-Caltech/B. Johnson

NASA's Voyager 2 spacecraft captured these views of Uranus (left) and Neptune (right) during its flyby of the planets in the 1980s.

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

The discovery includes the observation of one moon orbiting Uranus – the first discovery of its kind in more than 20 years – and two discovered in the orbit of Neptune.

Scott S. said: “The three newly discovered moons are the faintest ever seen around these two icy giant planets using ground-based telescopes,” said Shepard, an astronomer at the Carnegie Institution. For Science, in A statement. “It required special image processing to reveal such faint objects.”

These discoveries will be useful for missions that may be planned to closely explore Uranus and Neptune in the future. Priority for astronomers Since it was only ice planets They were 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 moon observed orbiting the ice giant, and is also likely the smallest, measuring 5 miles (8 kilometers) across. 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 one of Shakespeare's characters, in keeping with the tradition of Uranus's moons bearing literary names.

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Sheppard observed Uranus in November and December while making observations with the Magellan telescopes at 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 Uranus' new moon S/2023 U1 using the Magellan Telescope on November 4, 2023. Uranus (top left) is just outside the field of view.

The Magellan telescopes also played a key role in helping Sheppard find the brighter of Neptune's two moons, S/2002 N5. The Subaru telescope, located on the dormant Mauna Kea volcano in Hawaii, helped Sheppard and his collaborators, astronomer David Thulin of the University of Hawaii, astronomer Chad Trujillo of Northern Arizona University, and planetary scientist Patrick Sofia Likoka of Kindai University in Japan, focus on Neptune's other moon. Very faint, S/2021 N1.

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

“Once the orbit of S/2002 N5 around Neptune was determined using the 2021, 2022 and 2023 observations, it was traced back to an object that had been observed near Neptune in 2003 but had been lost before it was confirmed to be orbiting the planet,” Sheppard said. .

The bright moon S/2002 N5 has a diameter of 14 miles (23 kilometers) and takes nearly nine years to complete an orbit around Neptune, while the dim moon S/2021 N1 has a diameter of about 8.7 miles (14 kilometers) and has a long orbit of about 27 years. Both would eventually get new names that referenced the Nereid sea goddesses from 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.

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

“Because the moons move within only a few minutes relative to background stars and galaxies, single long exposures are not ideal for taking deep images of moving objects,” Sheppard said. “By stitching together 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 far-angular orbits of the moons, Sheppard hypothesized that the satellites were pulled into orbit around Uranus and Neptune by the gravitational influence of the giant planets shortly after their formation. The outer moons orbiting all the giant planets across our solar system—Jupiter, Saturn, Uranus, and Neptune—share similar configurations.

“Even Uranus, which is tilted on its side, has a similar number of moons to the other giant planets orbiting our sun,” Sheppard said. “Neptune, which was struck by the distant Kuiper Belt object Triton — an ice-rich body larger than Pluto — an event that could have disrupted its lunar system, likely has exomoons that look similar to its neighbors.”

Some of the moons surrounding the giant planets are likely fragments of larger moons that were struck by asteroids or comets and broke off.

Understanding how giant planets capture their moons is helping astronomers piece together the chaotic early days of our solar system.

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