Astronomers just spotted three new moons circling the furthest planets, Uranus and Neptune, in our solar system’s family.
The scoop includes a solo moon trailing Uranus—the first such find in over two decades—and a duo orbiting Neptune.
Scott S. Sheppard, a star-gazer at the Carnegie Institution for Science, reported, “These three moons are the dimmest ever seen around these ice giants with earthbound scopes.” He added, “We needed some fancy image tweaks to spot these elusive objects.”
These finds are gold for any upcoming treks to probe Uranus and Neptune up close, something space peepers have been itching to do since the ’80s Voyager 2 flybys.
The International Astronomical Union’s Minor Planet Center broke the news of the trio on February 23.
This latest Uranian moon, the 28th we’ve clocked orbiting this ice behemoth, might be the runt of the litter at a mere 5 miles (8 kilometers) wide. Known as S/2023 U1 for now, it takes a long 680 Earth days for a full Uranus lap. Future plans? It’s gonna snag a Shakespearean tag, as is tradition for Uranus’ moons.
Sheppard glimpsed the Uranian moon in late fall, using Chile’s Magellan telescopes at Las Campanas Observatory. He teamed up with Marina Brozovic and Bob Jacobson from NASA’s Jet Propulsion Lab in California to pin down the moon’s path.
The same Magellan glass helped Sheppard nab the shinier of Neptune’s new moons, S/2002 N5. Meanwhile, the Subaru telescope on Hawaii’s sleepy Mauna Kea volcano gave a hand to Sheppard and his gang—astronomer David Tholen from Hawaii Uni, Chad Trujillo from Northern Arizona Uni, and planetary scientist Patryk Sofia Lykawka from Japan’s Kindai Uni—to lock onto the other, fainter Neptunian moon, S/2021 N1.
With these two moons, Neptune now boasts 18 known natural satellites. They popped up in September ’21, but it took a few more telescope dates over the years to confirm they’re really hanging around Neptune.
“After we pinned down S/2002 N5’s Neptune dance using the 2021, 2022, and 2023 sightings, we matched it to a blip seen near Neptune in 2003, but that one got away before we could call it a moon,” Sheppard explained.
The brighter S/2002 N5 is a 14-mile (23-kilometer) chunk of rock, taking almost nine years to spin around Neptune. The dimmer S/2021 N1 is about 8.7 miles (14 kilometers) across, with an epic 27-year orbital trek. They’ll both snag names linked to Nereid sea sprites from old Greek tales, keeping with Neptune’s sea-god theme.
To spot all three moons required stacks of quick, five-minute photo snaps spread over a few hours on separate nights.
Sheppard pointed out, “Since moons shift a tad against the starry backdrop within minutes, you don’t want just one long snap for deep space shots of moving targets.” He said, “Layering these snaps makes stars and galaxies drag a tail in the pics, and moon-like movers close to the host planet pop out as dots, clear from the background fuzz.”
By looking at the far-flung, wonky orbits of these moons, Sheppard suspects they got yanked into their planetary dances by Uranus and Neptune’s mighty gravity soon after the planets themselves took shape. The far-out moons of all the gas giants—Jupiter, Saturn, Uranus, and Neptune—show a family resemblance in their orbits.
Sheppard notes, “Uranus, all tilted over, still has moons kinda like the rest of the solar system’s big shots.” And he adds, “Neptune, which likely snagged the far-off Kuiper Belt wanderer Triton—an icy chunk bigger than Pluto—might’ve had a moon system shake-up, but its distant moons still look like those of its planetary neighbors.”
Some moons might be leftovers from bigger moons that got into cosmic fender-benders with asteroids or comets and then shattered.
Figuring out how these heavyweight planets got their moons gives astronomers clues to piece together our solar system’s wild youth.
