As if it were a kind of “cosmic dew” , a team of scientists has discovered radioactive dust deep in the seabed that suggests that our planet is moving through a giant radioactive cloud as a result of stellar explosions; what we know as supernovae. Thus, continuously for the last 33,000 years, space has left a trace of a rare isotope of wrought iron in ancient supernovae: iron-60.
Radioactive elements synthesized in massive stars are expelled into space through stellar winds and supernova explosions. Our solar system moves through the interstellar medium and collects these extrasolar products. Precisely one of those substances is iron-60 that does not occur naturally on Earth.
While the isotope is radioactive and takes 15 million years to decompose, it is not dangerous to humans , according to experts at the Australian National University , as it is a very light dust.
The team examined sediments known to date back 33,000 years using a sensitive mass spectrometer and found traces of the iron-60 isotope that forms when stars die.
Australian researchers found traces of iron-60 about 2.6 million years ago, and possibly another about 6 million years ago, suggesting that our planet had traveled through rain clouds from nearby supernovae. They also found the strange isotope in lunar soil samples returned to Earth by the Apollo 12, 15 and 16 missions, and in snow tests from Antarctica.
“For the past thousands of years, the solar system has been moving through a denser cloud of gas and dust, known as the Local Interstellar Cloud, whose origins are unclear. If this cloud had originated during the last million years from a supernova, it would contain iron-60, so we decided to look for more recent sediments to find out ”, clarify the authors in their study published in the journal PNAS.
After probing several deep-sea sediments from two different locations dating back 33,000 years using an extremely sensitive mass spectrometer, they found clear traces of iron-60; and its distribution coincided with the recent journey of the Earth through the Local Interstellar Cloud.
However, the radioactive isotope extended much further back over the entire 33,000-year measurement period.
“The lack of correlation to solar system time in the current Local Interstellar Cloud seems to raise more questions than it answers. First, if the cloud was not formed by a supernova, where did it come from? And second, why What is iron-60 so evenly distributed in space? “the scientists wonder.
Perhaps it is that “iron-60 could originate from even older supernova explosions, and what we measure is some kind of echo.”
We will have to wait for more studies to clarify it.
Referencia: A. Wallner et al. 60Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity. PNAS, published online August 24, 2020; doi: 10.1073/pnas.1916769117
