Scientists have discovered that diamond melts at a temperature more than 1,300 degrees Fahrenheit (700 degrees Celsius) lower than previously believed. This new finding resolves a long-standing puzzle between experimental results and computer models. Researchers used powerful lasers to subject tiny synthetic diamond samples to extreme heat and pressure, allowing them to measure the melting point with greater accuracy. The results, published in the journal Nature Physics, bring experimental data in line with theoretical predictions and offer a clearer picture of how diamond behaves under intense conditions. In the study, scientists used ultraviolet lasers to shock diamond samples, creating temperatures hotter than the surface of the sun and pressures greater than those found at the cores of planets like Neptune and Uranus. They observed a noticeable increase in the diamond's reflectivity, which indicated melting. Researchers also measured how brightly the diamonds glowed, using that information to determine the melting temperature. Additionally, they used X-ray diffraction to examine the atomic structure of the samples. They found that diamond does not transform into a different solid form of carbon before melting, likely because the transformation requires an enormous amount of energy. These findings have important implications for nuclear fusion research. Scientists use diamond capsules in laser experiments to achieve the extreme conditions necessary for fusion reactions. The study revealed that under certain pressure and temperature ranges, diamond exists as solid chunks floating in a sea of liquid carbon. This liquid carbon is metallic and denser than diamond, suggesting that in some hypothetical situations, solid diamond could float in liquid carbon, similar to ice floating in water. Understanding how diamond behaves under extreme conditions is also key to studying the interiors of ice giant planets like Uranus and Neptune. Scientists believe that these planets may have layers of liquid carbon and even "diamond rain" in their deeper atmospheres. The new research provides a better understanding of the carbon cycles and internal structures of these distant worlds, helping scientists refine models of planetary formation and evolution.