A Japanese oil exploration company recently unearthed some samples from the Pacific and donated them to researchers. These researchers, led by Dr. Anton Wallner from the Australian National University, then found the first evidence of a radioactive isotope of plutonium that originally came from space. Scientists are now trying to understand what this isotope and another fascinating extraterrestrial might have created, and what this might have meant for the cosmic neighborhood of Earth a few million years ago.
In addition to the plutonium, Dr. Wallner and his team also made a unique form of iron. This iron isotope also appears to come from a different source than the plutonium obtained from the same sample.
Discussion of how to find the age of certain elements.
Photo credit: Ars Technica YouTube channel
The iron isotope iron-60 is the most common of the two radioactive isotopes found. It has a half-life of around 2.6 million years, but was found in rocks, lunar samples, and even in snow. Given the (relatively) short half-life of this form of iron, it seems clear that the samples found in various locations around the world were not part of the material that formed the earth about 4 billion years ago.
Iron is one of the heavier elements, and this particular isotope of iron is likely made in a supernova. Dr. Wallner and his team also compared the iron-60 in their most recent sample with those previously described and found that they likely came from various supernova events. One took place about 3 million years ago while another took place about 6 million years ago.
UT video about the different types of supernova.
The iron-60 produced in these explosions reached Earth, where it rained and was eventually absorbed by the ocean floor. Such an active nearby cosmic neighborhood is very different from the present calm part of the galaxy through which our planet sails and has implications for the evolution of life as well as the chemical makeup of the earth itself.
Plutonium is even more fascinating than iron. The specific isotope that Dr. Wallner and his team have found is actually the most stable of the plutonium isotopes – P-244. However, it does not naturally exist on earth. So if you find it in terrestrial rocks, it was created elsewhere.
UT video about neutron star fusions.
For much heavier elements like plutonium, most scientists think that even a supernova is not powerful enough to create it. The current hypothesis is that extremely heavy elements are formed in extremely violent events such as the merging of two neutron stars, which can also generate gravitational waves.
However, this is one of the first pieces of evidence of a violent event occurring close enough to Earth that the planet itself was colonized by this relatively short-lived isotope, whose half-life is 81 million years. This puzzle can be solved in two ways: Either scientists need to rethink how plutonium-244 was formed, or they need to reevaluate whether the Earth has been close to an immense explosion at some point in the not-too-distant past.
RAS video of the stars around us.
Photo credit: Royal Astronomical Society YouTube channel
In any event, these results have been hailed in the scientific community as the culmination of years of searching for precisely these types of samples. The world can thank a Japanese oil exploration crew for excavating one of the most interesting pieces of rock they could have. We can also look forward to further evidence that will help inform the genesis of these otherworldly radioisotopes.
Learn more:
ANU – Alien radioactive element prompts rethinking when creating
OPB / NPR – Freshly made plutonium from space on the ocean floor
Science – 60Fe and 244Pu deposited on Earth are limiting R-process yields from recent supernovae nearby
UT – A supernova that exploded dangerously close to Earth 2.5 million years ago
UT – Exploding Stars are titanium factories
Mission statement:
Incorrect color residue from a Supernova N132D.
Photo credit: NASA / JPL-Caltech / Harvard-Smithsonian CfA
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