A team of physicists has resolved a long-standing scientific puzzle over exactly how diamond melts under extreme pressure, using powerful laser-driven shock waves to observe the process in unprecedented detail and uncovering behavior researchers say defied expectations.

The research, led by physicist Marius Millot at Lawrence Livermore National Laboratory, was published this week in the journal Nature Physics. The team used the OMEGA Laser Facility at the University of Rochester’s Laboratory for Laser Energetics to blast tiny diamond samples with laser pulses, generating shock waves that produced pressures ranging from 600 gigapascals to 1.8 terapascals, more than three times the pressure found at the center of the Earth.

Diamond, the hardest naturally occurring mineral on Earth, is notoriously difficult to melt, requiring conditions far beyond anything found naturally at the planet’s surface. Scientists first successfully melted diamond in a 2007 experiment using a laser to strike it with a shock wave at 750 gigapascals of pressure, more than double the ambient pressure at Earth’s inner core. A follow-up study in 2009, led by LLNL physicist Jon Eggert, directly measured diamond’s melting temperature for the first time, but that measurement created a new problem: it disagreed with quantum-mechanical theoretical predictions by roughly 20%, a gap that persisted despite years of increasingly sophisticated computer modeling.

Millot’s team set out to resolve that discrepancy using significantly improved diagnostic tools that allowed them to track diamond’s atomic structure in real time as it melted, something earlier experiments lacked the sensitivity to capture. Using X-ray diffraction, the team measured how the diamond’s crystal structure evolved as pressure increased, alongside measurements of shock speed, temperature, density and optical reflectivity, all captured within a window lasting only a billionth of a second.

The new measurements placed diamond’s melting temperature at approximately 7,300 Kelvin at 1 terapascal of pressure, a figure notably lower than earlier experimental results and one that, for the first time, closely matched theoretical predictions. Eggert, a co-author on the new study, acknowledged the significance of the correction. “It was frustrating to discover that our original temperature measurements were off,” Eggert said, adding that the improved data quality made possible by the team’s updated diagnostics ultimately made the correction worthwhile.

Beyond resolving the temperature discrepancy, the experiment answered a second long-standing question about diamond’s behavior under extreme pressure. Theoretical models had predicted that, at pressures around a terapascal, diamond’s rigid atomic lattice should temporarily shift into a different crystalline form of carbon known as BC8 before fully melting into a disordered liquid. Some earlier experiments had been interpreted as possible evidence of that transition occurring above roughly 900 gigapascals.

Millot’s team found no evidence of a substantial BC8 phase. Instead, the X-ray data showed that diamond’s crystal structure remained in its familiar cubic lattice for as long as any solid structure could be detected at all, with solid diamond and liquid carbon simply coexisting until the material had fully melted. Millot attributed the finding to the extremely rapid, single-shock nature of the experiment. “We think that is because the sample does not have time to change when it only experiences a single shock,” Millot said, explaining that the diamond effectively becomes trapped in its original structure rather than transforming into the intermediate BC8 phase theory had predicted.

The researchers say that outcome likely reflects the sheer energy required to break and rearrange diamond’s unusually strong carbon-carbon bonds, a process theory suggests would be needed to form the BC8 structure. Under the fleeting timescale of the shock-compression experiment, the diamond appears to melt before that structural rearrangement has any opportunity to take place.

The findings also revealed an unexpected parallel between diamond and ordinary water ice. Under the extreme pressures studied, solid diamond proved less dense than the liquid carbon it melts into, mirroring the way conventional ice is less dense than liquid water and floats on its surface. The researchers say this implies solid diamond could similarly float atop a pool of molten carbon under the right conditions, and it also produces a related counterintuitive effect: across part of diamond’s melting range, increasing pressure actually lowers the temperature required for it to melt.

Beyond its implications for fundamental physics, the research carries direct practical applications. Diamond is used to encase fuel pellets in inertial confinement fusion experiments, where the material is compressed under pressures similar to those studied in the new experiment. More accurate models of how carbon behaves as those capsules implode could improve the design of future fusion experiments. According to the study’s authors, simulations incorporating the corrected carbon behavior suggest that predicted fusion energy gain could increase by up to threefold. Millot said the findings suggest researchers could achieve full diamond melting in fusion experiments using somewhat slower initial shocks, a change that would make the fusion fuel more compressible and could increase the maximum energy yield achievable using the same amount of laser energy.

The research also carries implications beyond Earth. Scientists believe carbon experiences pressure and temperature conditions similar to those recreated in the experiment deep inside ice giant planets such as Neptune and Uranus, meaning the improved understanding of diamond’s high-pressure behavior could help refine models of those planets’ internal structure and composition.

Separately, researchers at Sandia National Laboratories have conducted related diamond-compression experiments using the extreme magnetic fields generated by that facility’s Z machine, and have reported experimental signatures suggesting diamond may take an additional intermediate step on its way to melting, a finding that appears to differ from the Livermore team’s conclusions and suggests the full picture of diamond’s high-pressure behavior may still require further study to fully resolve.

ANAHEIM, Calif. — Disney gave fans their first extended look at “Frozen 3” on Friday night, revealing that Anna and Kristoff’s long-awaited wedding will open the film before a mysterious new villain and an unexplored, dangerous realm pull the characters far from their kingdom of Arendelle.

The reveal came during Disney’s D23 Entertainment Showcase at the Honda Center in Anaheim, where stars Idina Menzel and Kristen Bell walked onto the stage together and performed a rendition of “Frozen Heart,” the song that opened the original 2013 film, before discussing the upcoming threequel in detail. Bell confirmed that Anna will marry Kristoff, referring to her love interest by his familiar nickname. “This royal wedding has been a long time coming,” Bell told the crowd, noting that Elsa will be by her sister’s side for the ceremony.

According to descriptions from outlets present at the event, the footage shown to the D23 audience opened on the night of Anna and Kristoff’s wedding, when the newlyweds come upon Elsa on a dock, studying a mysterious stone that appears to open a portal into an entirely new, snow-covered dimension. Menzel, who plays Elsa, described the realm awaiting the characters as considerably more perilous than anything her character has previously encountered. “A frozen land more wild and dangerous than anything Elsa has ever created,” Menzel said, teasing the scale of the adventure awaiting Anna, Elsa, Kristoff, Olaf and Sven in the new film.

Once the characters step through the portal, they are quickly confronted by a new antagonist. Outlets in attendance described the character as a woman with short black hair and a dark, dramatic cape, though her face was not shown during the footage. In the scene, the new villain approaches the group from atop a snowy peak and addresses Anna and Elsa directly, acknowledging their identity as Arendelle’s ruling sisters in a tone that made clear she was not a friendly presence.

The presentation also confirmed a lighter subplot involving fan-favorite snowman Olaf. Josh Gad, who voices the character, joined Bell and Menzel on stage to perform a new song dedicated to a character named Samantha, described as Olaf’s love interest in the upcoming film. The addition appears to be a nod to a running joke from “Frozen 2,” in which Olaf briefly mentions an imaginary friend named Samantha during the film’s post-credits scene.

“Frozen 3” is scheduled for release November 24, 2027, timed to arrive just ahead of the Thanksgiving holiday in the United States, mirroring the release strategy Disney used for the franchise’s two previous installments. The returning voice cast includes Bell as Anna, Menzel as Elsa, Jonathan Groff as Kristoff and Gad as Olaf, with the story once again centered on the fictional kingdom of Arendelle, even as this chapter is expected to take the characters well beyond its borders for much of the film.

Friday’s reveal builds on concept art Disney first showed for the project two years earlier, also at D23, depicting Elsa and Anna riding separately toward a distant white palace, with Elsa mounted on the water spirit Nokk and Olaf perched on the back of Anna’s horse. At that earlier presentation, “Frozen 3” co-director Jennifer Lee said the story had grown complex enough that it would take two films to resolve the questions left open at the end of “Frozen 2,” a comment that first confirmed a fourth “Frozen” film was also in development alongside the third.

Kristen Bell has previously discussed the film’s development in press interviews, telling Variety in October 2025 that production was getting underway, though she had not yet heard any of the film’s music at that point. Bell also used that interview to deny reports claiming she would be paid $60 million to reprise her role as Anna, though she did not disclose her actual compensation for the film.

The “Frozen” franchise ranks among Disney’s most commercially successful properties, with its first two films combining for more than $2.76 billion in worldwide box office receipts and two Academy Awards. “Frozen 2,” released in 2019, remains one of the highest-grossing animated films in box office history.

With “Frozen 3” still more than a year from release, Disney has not yet revealed the new villain’s identity, name or full motivations, nor detailed the specific nature of the frozen realm introduced in Friday’s footage. For now, fans have confirmation of a wedding, a new romance for Olaf, and the outline of a threat serious enough to pull Anna and Elsa away from Arendelle once again, with additional details expected to emerge as the film moves closer to its Thanksgiving 2027 release.