Earth appears to be traveling through the debris of ancient supernovae

Continuously, for 33,000 years, space has seeded the Earth with a rare isotope of wrought iron in supernovae.

This is not the first time that the isotope, known as iron 60, has dusted our planet. But it contributes to a growing body of evidence that such a dusting is taking place – that we’re still moving through a cloud of interstellar dust that could have originated from a supernova millions of years ago.

Iron 60 has been the subject of several studies over the years. It has a half-life of 2.6 million years, which means it decays completely after 15 million years – so any samples found here on Earth must have been deposited elsewhere, as there There is no way that iron 60 could have survived the formation of the planet 4.6 billion years ago.

And deposits were found. Nuclear physicist Anton Wallner of the Australian National University has already dated the seabed deposits to 2.6 million and 6 million years ago, suggesting that supernovae debris had rained on our planet at those times.

But there is more recent evidence of this stardust – much more recent.

It was found in the Antarctic snow; according to the evidence, he must have fallen in the past 20 years.

And, a few years ago, scientists announced that iron-60 had been detected in space around Earth, measured over a period of 17 years by NASA’s Advanced Composition Explorer.

Now Wallner has found more of this stuff, in five deep-water sediment samples from two places dating back 33,000 years ago. And the amounts of iron 60 in the samples are fairly constant over the entire period. But this finding actually poses more questions than it answers.

Earth, you see, 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 exploding stars, it is reasonable to expect that it sprinkles the Earth with a very light rain of iron-60. This is what the Antarctic detection suggested; and this is what Wallner and his team sought to validate by examining ocean sediments.

But if the local interstellar cloud is the source of iron-60, there should have been a big surge when the solar system entered the cloud – which, according to the team’s data, likely happened over the last few years. Last 33,000 years. At the very least, the older sample should have had significantly lower iron-60 levels, but it didn’t.

It is possible, the researchers note in their paper, that the local interstellar cloud and supernova debris coincide, rather than a single structure, with the debris remaining in the interstellar medium of supernovae that took place millions of years ago. ‘years. This would suggest that the local interstellar cloud is not a slight remnant of a supernova.

“There are recent papers that suggest that iron-60 trapped in dust particles could bounce back into the interstellar medium,” Wallner said.

“So the 60 iron could come from even older supernova explosions, and what we’re measuring is kind of an echo.”

The best way to find out, the researchers note, is to look for more iron-60, covering the gap between 40,000 years ago and around a million years ago.

If the abundance of iron-60 increases further in time, it would suggest ancient supernovae.

However, greater abundance more recently would suggest that the local interstellar cloud is the source of iron-60.

The research was published in the Proceedings of the National Academy of Sciences.