The planet Uranus is a weird place. Not only does it roll around the Sun on its side once every 84.3 Earth years, it also sports a spindly set of rings corralled in some places by strange little moons. Two of those rings, the μ (mu) and ν (nu) rings are incredibly faint, which makes them challenging to study.

Observations by Hubble Space Telescope (HST), the James Webb Space Telescope (JWST), combined with data from the Keck Observatory on Mauna Kea in Hawai’i, show that those two rings are two different colors. The observations that revealed the differences are reflectance spectra that measured the sunlight reflected from the ring’s particles. “By decoding the light from these rings, we can trace both their particle size distribution and composition, which sheds light on their origins, offering new insight into how the Uranian system and planets like it formed and evolved,” said Imke de Pater, professor at the University of California, Berkeley, and lead author of a paper discussing the findings.

The μ ring looks blue in the spectra and is made largely of icy particles. It likes about 98,000 kilometers from Uranus’s cloud tops. Interestingly, Saturn’s E ring is also blue, and its particles come from the moon Enceladus. The Uranian μ ring and Saturn’s E ring are the only two such rings known in the Solar System.

The ν ring, which appears red in the spectra and lies about 67,000 kilometers from Uranus’s cloud tops is dusty and consists of 10–15% carbon-rich organics. The differences in composition between the two rings raise a lot of questions about the origins of their materials and the mechanism for their presence in the two rings.

*Uranus outer ring system as imaged with JWST on February 2, 2025 in broadband filters centered at 3.2 mm (left) and 1.5 mm (right). Both μ and ν rings are indicated by arrows. Left: Image F322W2: to visualize the entire system, Uranus and its main ring system intensity is diminished by a factor of 100. Right: Image F150W2: In order to see the ings above the scattered light from Uranus and the main rings, this image has gone through a high-pass filter. Credit: NASA, ESA, Image processing: Imke de Pater, Matt Hedman*

How Could they Be So Different?

According to de Pater, the sources are very different. “The ν ring material is sourced from micrometeorite impacts on and collisions between unseen rocky bodies rich in organic materials, which must orbit between some of the known moons,” she said. “One interesting question is why the parent bodies sourcing these rings are so different in composition.”

The source of ice particles for the μ ring turns out to be the icy moon Mab. It was discovered in 2003 via HST observations and based on the most recent observations, appears to be mostly water ice. Since it orbits the same distance from Uranus as the μ ring, it likely renews the ring particles with tiny ice grains that get knocked off Mab’s surface by small impacts.

*Mab, a small moon orbiting Uranus and source of material for the μ ring. Courtesy NASA/ESA/STScI*

Why is Mab so different from Uranus’s other inner moons? Those are mostly rocky bodies, and Mab’s composition remains something of a mystery. The answers will come from further studies of the dynamical evolution of the outer Solar System over time. Flyby images would also help scientists understand more about the compositions of Mab and other moons circling Uranus.

The History of the Uranian Rings

Uranus’s rings were the second set to be discovered in the Solar System, after Saturn’s. They were first observed in 1977, and the Voyager 2 spacecraft later found two more rings, during its flyby in 1986. HST later found two outer rings in observations beginning in 2003. Unlike Saturn’s collection, Uranus’s rings are faint and narrow, some only a few kilometers wide. Some of the rings are optically dense (meaning they’re thicker) while others are very thin.

An annotated version of the Uranian moons. Public Domain.

The Uranus ring system is probably quite young. Some estimates put its age at around 500 to 600 million years old and it almost certainly originated from the collisions of several moons that once orbited the planet. Those collisions resulted in smaller chunks, which themselves collide to create smaller particles and dust. Eventually, that material collected into rings that get continually refreshed by other, smaller collisions with Mab and another so far unobserved object in the system. Planetary scientists are still working to understand the mechanism that keeps these rings so narrow. Shepherd moons may play a role, but that has yet to be proven since not every one of the narrow rings is bounded by a pair of small moons.

Scientists using Keck, JWST, and HST will continue to monitor changes in the Uranian rings, including the shifts in brightness, which could indicate renewed activity in the system. “We see hints that the µ ring’s brightness changes over time, and what could be causing those changes is still a mystery” added Matt Hedman, co-author and professor at the University of Idaho.

For More Information

New Study Uncovers Distinct Origins of Uranus’s Two Outer Rings

Characterization of the Outer Uranian Rings in the Visual and Near-IR Using Keck, JWST, and HST Observations

Cole Tomas Allen, the suspected gunman who rattled Washington’s leaders by exchanging gunfire with officials just outside a press gala late Saturday, had made a long journey from Southern California and written a “manifesto” threatening Trump administration officials before the attack, officials said.

Allen, a 31-year-old Caltech graduate and high school tutor from Torrance, is believed to have taken a train first to Chicago and then to D.C. before checking into the Washington Hilton with two guns he had previously purchased, authorities said.

The attacker managed to bypass several layers of security at the White House Correspondents’ Assn. dinner before being taken down by armed agents outside the ballroom where President Trump and an array of other top federal officials were seated.

Members of law enforcement respond during the White House Correspondents Dinner on Satruday.

(Tom Brenner / Associated Press)

Neither Allen nor a legal representative for him could be reached for comment Sunday.

According to Trump, Allen wrote a “manifesto” prior to the attack, and shared it with family. His brother flagged it to local law enforcement in New London, Conn., late Saturday. The New York Post reported that Allen described himself in the document as the “Friendly Federal Assassin” and revealed he intended to kill Trump administration officials.

New London Police Deputy Chief John Perry said that around 10:30 p.m. a man came to the lobby of the agency’s headquarters to report that he’d received a troubling email from Allen. The relative initially thought it was spam, but then saw the news of what had unfolded in D.C. and felt he needed to report it.

Perry would not say what was in the email, and did not know exactly what time it was sent, but said that the relative said he only saw and opened it around 10 p.m. “I think he was watching what was going on and kind of put 2 and 2 together and said, ‘I need to go to my local PD,’” Perry said.

Police officials provided the email to the Secret Service and FBI, he said. Trump, who like other top officials was escorted from the ballroom unharmed, said the document would be released, but it had not been as of Sunday.

One officer was shot during the incident at “close distance with a very powerful gun,” but saved by his ballistic vest and was in “great shape” and “high spirits” afterward, Trump said late Saturday. The president called the suspect a “thug that attacked our constitution.”

Jeanine Pirro, the top federal prosecutor in D.C., said the suspect faces two criminal charges of using a firearm in a violent crime and assaulting a federal officer using a dangerous weapon. Officials said that more charges could follow and that an initial court appearance is likely Monday.

FBI agents arrive at a house in Torrance that is connected to shooting suspect Cole Tomas Allen.

(Robbin Goddard/Los Angeles Times)

Late Saturday, both local and federal law enforcement, including the FBI, swarmed the Torrance residence where Allen is believed to have lived with his family, with officers clearing the road and stringing police tape along part of the street. A man who responded to a knock on the front door said, “Not right now,” and declined to comment further.

The thwarted attack marked the latest in a string of incidents in which gunmen have gotten dangerously close to Trump, renewing questions about the safety and security of the president at a time of intense political division at home and roiling conflicts abroad.

Trump was grazed on the ear by a bullet at a presidential campaign event in Butler, Pa., in 2024 — the first of two attempts on his life during the campaign. The other involved a gunman targeting the president as he golfed in Florida, before federal agents intervened. Earlier this year, a gunman was killed at the president’s Mar-a-Lago residence after breaching a security perimeter.

On Sunday, questions swirled as to how such a security lapse could happen yet again — and whether large, high-profile events are safe for top officials in a nation where firearms are easy to obtain and ubiquitous.

Acting Atty. Gen. Todd Blanche, in an interview on NBC’s “Meet the Press” Sunday morning, said that federal authorities believe the suspect had set out alone “to target folks that work in the administration, likely including the president,” but that a motive was still being determined and evidence still being gathered — including from devices taken from Allen and in interviews with people who know him.

“As of now, we don’t have any connection to any particular policy directive of President Trump or Iran or anything else that we’re doing in this country, but we are looking into it,” he said.

Blanche also downplayed the threat posed to Trump, other officials in the room such as Vice President JD Vance and First Lady Melania Trump, and the hundreds of other attendees to the annual event. He said the gunman was stopped almost immediately after he darted past metal detectors and federal agents — a dramatic moment that was captured on surveillance video and posted online by the president.

Agents stand guard after an incident at the White House Correspondents’ Dinner.

(Andrew Harnik / Getty Images)

“Let’s not forget that the suspect didn’t get very far. He barely broke the perimeter,” Blanche said. “And so while this was extraordinarily dangerous and put a lot of lives at risk and there’s no doubt that that’s something that we’re going to have to learn from over the next couple weeks, the system worked. We were safe, President Trump was safe. His Secret Service agents kept him safe. All of us were safe.”

Blanche’s assessment of the attacker’s breach of security — which he said was only “by a few feet” — was disputed by some.

According to other attendees, including Times journalists, event staffers were checking tickets, though not very thoroughly, at multiple points prior to escalators that descended to the metal detectors where Allen allegedly bolted past armed security.

The detectors were right outside the event hall and where the bathrooms for the event were located, and the assailant was taken to the ground about 10 to 15 feet beyond them, attendees said. The shots — including two from the gunman, according to Blanche — were heard in the ballroom.

Allen, who graduated from Caltech in 2017 with a degree in mechanical engineering and is registered to vote with no party preference, made a $25 political contribution earmarked for then-Vice President Kamala Harris’ campaign challenging Trump for the presidency in 2024.

While at Caltech, he was a teaching assistant and a member of the school’s Christian fellowship and the Nerf club, according to his LinkedIn profile. He later studied computer science as a postgraduate student at Cal State Dominguez Hills.

Allen was named teacher of the month in December 2024 at C2 Education, which specializes in college test preparation, tutoring and academic advising. A representative for C2 Education was not immediately available for comment.

According to the New York Post, Allen himself had derided the event security in his writings beforehand, describing finding far less security at the hotel than he had expected when he arrived, armed, to check in.

U.S. Secret Service agents patrol the North Lawn at the White House after a shooting incident outside the ballroom at the annual White House Correspondents’ Assn. Dinner in Washington on Saturday night.

(Tom Brenner / Associated Press)

“I expected security cameras at every bend, bugged hotel rooms, armed agents every 10 feet, metal detectors out the wazoo. What I got (who knows, maybe they’re pranking me!) is nothing. No damn security. Not in transport. Not in the hotel. Not in the event,” he wrote, according to the Post. “I walk in with multiple weapons and not a single person there considers the possibility that I could be a threat.”

“I could have brought a damn Ma Deuce in here and no one would have noticed s—,” wrote the author, referring to a .50 caliber machine gun.

Authorities did not detail Allen’s alleged travel route to D.C., other than to say it was by train. In response to questions about whether Allen had taken Amtrak to get to Washington and whether his luggage would have undergone any security screening, Amtrak said only that it is cooperating with federal authorities.

Trump also zeroed in on security at the hotel being inadequate, in addition to posting the video of the suspect rushing past security and multiple pictures of him detained on the floor of the hotel.

While praising the federal agents who took the attacker down, Trump suggested that events with top U.S. officials should be held in more secure facilities — such as the giant ballroom he is trying to build on the White House grounds after demolishing the former East Wing.

“What happened last night is exactly the reason that our great Military, Secret Service, Law Enforcement and, for different reasons, every President for the last 150 years, have been DEMANDING that a large, safe, and secure Ballroom be built ON THE GROUNDS OF THE WHITE HOUSE,” Trump wrote on social media Sunday. “This event would never have happened with the Militarily Top Secret Ballroom currently under construction at the White House. It cannot be built fast enough!”

Weijia Jiang, president of the correspondents’ association, said in a statement Sunday that the group’s board “will be meeting to assess what happened and determine how to proceed.” She also thanked the U.S. Secret Service and other law enforcement for keeping people safe, and praised journalists in the room for leaping to work to inform the public of what had occurred.

Brian Levin, a professor emeritus of Cal State San Bernardino and founder of the Center for the Study of Hate and Extremism, said “newer and real, but mostly loner” threats of “hard left violence” against public officials have been on the rise.

“During this polarized era, self radicalization, psychological factors, weapons access, and the normalization of aggression have been recurrent recent themes as both extremist motivated homicides, threats against public officials, hate crime killings and aggravated bias assaults have all increased,” he said.

However, the threat is less organized and intertwined with peaceful civil society movements than some in the Trump administration have tried to portray, he said.

After Allen was first named in connection with the D.C. incident late Saturday, more than 100 journalists and other curious observers stood behind lines of yellow police tape at both ends of the Torrance street where he is believed to have lived — and where FBI agents had arrived in unmarked cars and armored vehicles about 9:45 p.m.

One local resident, who identified herself as Bora but declined to give her last name, said Sunday that it had been “loud until after midnight” in the usually quiet neighborhood. “Helicopters were overhead and people were out all night.”

She said she often waved to the friendly residents of the home agents had swarmed, who seemed “nothing special, just normal.”

Times staff writers Richard Winton, Ben Wieder and Justine McDaniel contributed to this report.