Rare plutonium from space found in deep-sea crust, study reveals

Element likely found its way to Earth following multiple supernovae explosions, Sam Hancock finds

This file photo from 2015 shows a remnant of the Tycho supernova (Nasa/Science News)

A rare radioactive plutonium isotope dating back millions of years has been found embedded in Earth’s crust, helping experts to understand how heavy metals form in the stars.

New research published in the research journal Science suggests the element known as plutonium-244 – discovered nearly 5,000ft below the Pacific Ocean – made its way to our planet following multiple supernovae explosions millions of years ago.

The element iron-60, a lighter metal known to form in stellar explosions, was also discovered at the site, according to the experts’ findings.

“Our data could be the first evidence that supernovae do indeed produce plutonium-244,” the study’s lead author, Dr Anton Wallner, said in a statement, adding that the element’s “story is complicated”.

“Possibly this plutonium-244 was produced in supernova explosions or it could be left over from a much older, but even more spectacular event such as a neutron star detonation,” he said.

Iron-60 has a half-life of approximately 2.5 million years before it decays, while plutonium-244 has a half-life of just over 80 million years.

This extended half-life is “long enough for most of it to remain from events of the past few million years but short enough that none is left from the time the Solar System was created,” the study’s co-author, Dr Michael Hotchkis of ANSTO’s Centre for Accelerator Science, added.

Dr Wallner, a nuclear physicist at the Australian National University, also suggested that plutonium-244 “was already in the interstellar medium before the supernova went off, and was pushed across the Solar System together with the supernova ejecta”.

Both of these elements are heavy and should have decayed into stable forms decades ago, he said, but given the state that they were found in, it is likely the cosmic event which caused them to land here happened just a few million years ago.

Speaking about the supernova, Dr Wallner said it “must have been spectacular at the time”.

“It must have been similar [in brightness] to the full moon, so you would see it even in daytime,” he added.

Further study of the isotopes and others like them could allow researchers to understand more about the Solar System’s past explosions.

What is plutonium-244?

Plutonium-244 is one of the heaviest elements on Earth. Its half-life of 80 million years is longer than any other plutonium isotope and all but three other actinide isotopes: uranium-235, uranium-238, and thorium-232.

Of the 244 particles that make up plutonium-244, 94 are protons and 150 are neutrons.

Trace elements of it were first discovered in its primordial state in the early 1970s.

“What is fascinating is that you find some six or 10 atoms which you can identify in the end as [being] not from Earth but from space,” Dr Wallner ended his statement by saying.

“And then you get some hints about where it had been produced and when it had been produced.”