Physicists have uncovered a pair of huge , still-radioactive isotopes in samples of deep-sea crust pulled up from 1,500 meters (nearly 5,000 feet) below the Pacific .
We’d expect to ascertain many heavyweight elements within the swirl of dust and gas that formed our planet eons ago – but most should have decayed into more stable forms many years ago . So finding examples in crust close to surface today raises some interesting questions.
The finding could tell us a thing or two about cataclysmic cosmic events happening within a couple of hundred light-years from Earth, and comparatively recently in our geological history. It could also shine a light- on the way atomic heavy-weights form.
You see, building atoms takes much of energy. Protons are often squeezed into helium under the type of gravity you may find in star, but stellar fusion will only take you thus far . to create a chunky behemoth like plutonium, you will need the type of energy which will deliver a machine-gun burst of neutrons.
There are a couple of conditions within the Universe under which this ‘rapid neutron capture’, or r-process, can occur, including supernovae and neutron star mergers.
Over the history of the Universe, many stars have crashed and popped to spill a thick dust of iron, uranium, plutonium, gold, and other fat atoms throughout the galaxy. So it’s to be expected that planets like Earth would have scooped up an better amount of them.
But not all elements are born same to same . Variations within the number of their neutrons make some more stable than others. Iron 60, for instance , may be a ‘blink and you will miss it’ quite isotope if you view it on the cosmic scale, with a half-life of just 2.6 million years before it decays into nickel.
Finding this short-lived isotope on our planet today – especially within the crust, just out of reach of recent artificial processes – would imply a comparatively recent delivery of iron fresh from the cosmos.
Iron 60 has appeared in rock samples before, dating back just a few of million years. it is also been seen in materials brought back from the lunar surface.
But to urge a better sense of the precise type of r-process that produced these specimens, it might pay to ascertain what other isotopes rained down with them.
Physicist Anton Wallner from the Australian National University led a team of researchers in search of latest samples of iron 60 to ascertain if they might identify isotopes of other heavy elements accessible .
What they found was plutonium 244, an isotope with a half-life of just over 80 million years – stable for plutonium, but hardly the type of element you’d expect to stay around since our planet came together 4.5 billion years ago.
In all, the team discovered two distinct influxes of iron 60 which had to possess arrived within the past 10 million years. Both samples were amid small but significant quantities of plutonium 244, each one in similar ratio.
Finding them together adds more detail than finding either apart. the quantity of plutonium in them is less than would be expected if supernovae were primarily liable for their production, pointing to contributions from other r-processes.
Exactly what was behind this particular sprinkle of alien space dust is left up to our imagination for now.
“The story is complicated,” says Wallner.
“Possibly this plutonium-244 was produced in supernova explosions or it might be left over from a way older, but even more spectacular event like a neutron star detonation.”
By measuring their respective radioactive fuses and making a couple of assumptions on the astrophysics behind their distribution, the researchers speculate the production of iron 60 is compatible with 2-4 supernova events going off between 50 & 100 parsecs (around 160 and 330 light years) of Earth.
This isn’t the 1st time iron 60 has indicated a supernova happening perilously accessible in recent history.
By watching the isotope in reference to other elements, we could slowly build a signature that tells us more about the crash-bang conditions of our neighborhood within the many millions years before humans began to pay close attention.
It’ll take more looking for alien isotopes, though.
“Our data might be the primary evidence that supernovae do indeed produce plutonium-244,” says Wallner.
“Or perhaps it had been already within the interstellar space before the supernova went off, and it had been pushed across the solar system along side the supernova ejecta.”
This research was published in Science.