Radioactive dust detected in the deep ocean points to our planet traveling through a massive cloud left behind by a supernova.
Over the last 33,000 years, a kind of “cosmic dew” has fallen continuously from space, spreading the Earth with a rare isotope called iron-60, which is only created after star explosions. This is the conclusion reached by a study that has just been published in the journal Proceedings of the National Academy of Sciences.
It is not the first time that this isotope has been detected here in our world. But it contributes to the belief that such dust is still falling on our heads today, as we are still moving through the interstellar cloud that could have originated from a supernova millions of years ago.
Iron-60 has been the subject of several studies in recent years. It has a half-life of 2.6 million years, which means that it completely disintegrates after 15 million years – so any sample found here on Earth must have been deposited from somewhere else, since there is no way to that iron-60 survived the planet’s formation 4.6 billion years ago.
Nuclear physicist Anton Wallner of the Australian National University and lead author of the new study previously dated the seafloor deposits 2.6 million and 6 million years ago, suggesting that supernova debris had rained down on our planet in those moments.
However, there is recent evidence that this stardust has been precipitating less long ago. For example, the remains found in Antarctic snow suggest that iron-60 should have dropped sometime in the last 20 years. And, a few years ago, scientists announced that iron-60 had been detected in space around the Earth, measured over a 17-year period by the Advanced Composition Explorer from NASA.
Now Wallner has found more material in five deep-sea sediment samples from two places dating 33,000 years ago. And the amounts of iron-60 in the samples are fairly constant throughout the period studied.
More questions than answers …
Earth is currently moving through a region called the Local Interstellar Cloud, made up of gas, dust, and plasma. If this cloud was created by the explosion of stars, then it is reasonable to expect that it is “dusting” the Earth with a very weak shower of iron-60.
But if the Local Interstellar Cloud is the source of iron-60, there should have been a sharp rise when the Solar System slipped inside the cloud, which, according to the team’s data, is likely to have occurred in the last 33,000 years. At a minimum, the oldest sample should have had significantly lower levels of iron-60. But it’s not like that.
A supernova is a stellar explosion that can manifest itself in a very remarkable way, even with the naked eye, in places on the celestial sphere where nothing in particular had previously been detected. For this reason, events of this nature were initially called stellae novae (“new stars”) or simply novae
First, if the cloud was not formed by a supernova, where did it come from? And second, why is 60-iron so evenly spread across space?
“There are recent articles that suggest that iron-60 trapped in dust particles could bounce off the interstellar medium”, Wallner affirms. So, iron-60 could originate from even older supernova explosions, and what we measure is some kind of echo. More data is needed to resolve these details.’
The best way to find out, the researchers note, is to look for more iron-60, filling the gap between 40,000 and a million years ago. If the abundance of this isotope grows as you go back in time, it would suggest an ancient supernova. Otherwise, the Local Interstellar Cloud would be the source.
Source: ScienceAlert
