A small rock sample retrieved from the Pacific Ocean floor in 1976 has become a crucial piece in understanding a significant cosmic event. This rock contains atoms of the plutonium isotope Pu-244, which offers insights into the collision of two neutron stars that occurred over a hundred million years ago.
Discovery of Plutonium Isotopes
The neutron star merger produced a kilonova, a powerful explosion that generates heavy elements, including isotopes of plutonium. The sample, composed of ferromanganese rock, was found to contain several hundred atoms of Pu-244, which has a half-life of 81.3 million years. This measurement allowed researchers from the Helmholtz-Zentrum Dresden-Rossendorf in Germany and Australia’s Nuclear Science and Technology Organisation (ANSTO) to estimate the timing of the explosion at nearly 100 million years ago.
Absence of Curium
In their analysis, the team noted the absence of curium-247, another element produced during the merger, which has a shorter half-life of 16 million years. Dr. Michael Hotchkis from ANSTO stated, “The absence of the curium radioisotope Cm-247, which was also produced in the explosion, tells us it happened a very long time ago. But not more than about 1 billion years ago; otherwise the Pu-244 would also be undetectable.”
Methodology and Analysis
To uncover the hidden Pu-244, the research team drilled three cores from the rock and conducted a detailed chemical analysis. They dated the cores using the beryllium isotope Be-10, which has a half-life of 1.5 million years, and discovered traces of the iron isotope Fe-60 in one core. Each core, measuring up to 3 cm, represented over ten million years of Earth’s crust growth. The remaining rock was imaged using computed x-ray tomography and encased in resin, allowing for thin layers to be cut, each corresponding to approximately 1 million years of growth.
Implications for Cosmic Events
This study not only confirms the existence of plutonium from a neutron star merger but also suggests that such cosmic debris can arrive on Earth in pulses. The continuous presence of Pu-244 throughout the rock layers indicates that this isotopic material has been falling to Earth since the merger event. The research team aims to find additional samples to further validate their findings, potentially uncovering more remnants of the r-process that produced these heavy elements. Future explorations, including lunar missions, may also provide further insights into the cosmic origins of elements found on Earth.
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Original source: universetoday.com
