The recent discovery of plutonium-244 in deep-sea sediment has sparked a cosmic mystery, revealing a rare ancient cosmic explosion that occurred at least 100 million years ago. This revelation, as Dr. Dominik Koll explains, is a testament to the power of scientific detective work and the mysteries that still surround the universe. The explosion, which could have been a supernova or a neutron star collision, produced some of the rarest elements in the universe, including plutonium-244, and scattered them across the sky, eventually reaching Earth and settling at the bottom of the ocean. The discovery of plutonium-244, a radioactive element with a half-life of 80 million years, was made possible by the VEGA AMS facility at ANSTO. This element is produced by rare violent reactions in which neutrons are captured rapidly, known as the R-process, which remains a mysterious process in nature. The dating techniques used to establish the timeframe of the explosion were similar to carbon dating but utilized other radioactive elements, such as beryllium-10, to determine the age of the sample layers. The team's previous work had isolated iron-60, another tracer of supernovae, in a sample of ferromanganese crust extracted from the Pacific Ocean floor. By combining the data, they found peaks of iron-60 at two specific depths, pointing to two nearby supernovae in the last ten million years. However, the plutonium-244 was evenly spread throughout the sample, suggesting an older event that had spread its debris more evenly across the interstellar medium. The absence of curium-247, another radioactive element created in giant explosions, further supported this hypothesis, as its half-life of 15.6 million years is less than a fifth of plutonium-244's, allowing for its decay over time. This discovery has sent theorists back to the drawing board, as it has ruled out four models, including a recently proposed collision of the Solar System with a dense interstellar cloud. Dr. Koll emphasizes the need for more models and experiments to unravel the truth behind this ancient cosmic event, highlighting the ongoing quest to understand the universe and its mysteries.
