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Radioactive Interstellar Dust Discovered In Freshly Fallen Snow In Antarctica


After the analysis of  recent snow deposits in Antarctica, a group of scientists from certain countries have discovered the presence of a material coming from outside our Solar System. They found  samples of a particular isotope of iron, iron-60, in freshly fallen snow. They were quite sure that it could only have fallen from outside our planetary system.

They suspected that such rare element showed up in Antarctica in the form of interstellar dust, and it appeared in the last 20 years. 

The most abundant type of iron found is iron-56, including 26 protons and 30 neutrons in its nucleus, and forms almost 92 percent of all iron. It is one of the four stable isotopes of iron. Iron-60, which they found,got an extra four neutrons and was lightly radioactive, decaying with a half-life of 2.6 million years.

This radioactive element could be created in certain nuclear processes and in supernovae. Astronomers have discovered it in interstellar space, however it was also found on Earth at the bottom of the sea (dating back 2–2.5 million years) and on the Moon. So such phenomenon  suggested that over the past few million years Earth had been showered with material from nearby supernovae, which should turn up in geological formations.

In the article  published in Physical Review Letters, detailing their discovery, the international team of researchers were interested in seeing if this “shower” continued to this day. To complete such mission, it was necessary for them to analyze material from an uncontaminated site. Therefore, they collected 500 kilograms (1,100 pounds) of Antarctic snow from the last 20 years, then they melted these samples. After analysis of the composition of the melt-water, they did find the unexpected iron-60.

The team looked at the most likely scenario for the abundance of this rare isotope. From nuclear power plants and nuclear weapons,  iron-60 could be produced, however, there was no global fallout to justify the excess of iron-60 seen in the sample from Antarctica. Upon such evidence, the scientists targeted at an interstellar source, suggesting  it rained down as dust.

The reason which made this research potentially very profound was that the insights we could glean into interstellar clouds and their enrichment from supernovae. The researchers thought that the radioactive iron-60 from steller explosions should be caught up as dust particles in the Local Interstellar Cloud. It’s thought that the Solar System crossed into the cloud roughly 40,000 to 50,000 years ago, and that we might have left it around 3,000 years ago – though we might still be skirting the edges. And in that time, the material had showered down on Earth as dust.

From the conclusion of their article, the team claimed that by ruling out terrestrial and cosmogenic sources, they had found, for the first time, recent iron-60 with interstellar origin in Antarctica.

With investigation of the ice cores from throughout this time-frame and comparison of the abundance of iron-60 from when we first entered the cloud to the current sample, it could possibly provide new information about the structure and even the origin of the interstellar dust clouds that streak across the Milky Way.

Source: Physics World