Iron and nickel vapours found in cold atmosphere of comets for first time

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Scientists have spoken of their “big surprise” after discovering iron and nickel vapours in the ultra-cold atmosphere of comets for the first time.

These heavy metals are usually associated with hot environments, but astronomers found atoms of nickel and iron in the clouds of dust and gas surrounding distant comets, more than 480 million kilometres from the Sun (about three times the distance between the Earth and the Sun).

The scientists also found nickel vapours in the atmosphere of 2I/Borisov – the second interstellar object known to have passed through the Solar System.

They said their “unexpected” findings, published in two papers in the journal Nature, could help shed more light on how the Solar System came into existence.

Jean Manfroid, from the University of Liege, Belgium, and lead author on one of the papers, said: “It was a big surprise to detect iron and nickel atoms in the atmosphere of all the comets we have observed in the last two decades, about 20 of them, and even in ones far from the Sun in the cold space environment.”

The detection of nickel (Ni) in the fuzzy atmosphere of the interstellar comet 2I/Borisov
The detection of nickel (Ni) in the fuzzy atmosphere of the interstellar comet 2I/Borisov (ESO/L Calcada/O Hainaut/P Guzik/M Drahus)

The scientists used data gathered by the European Southern Observatory’s Very Large Telescope to analyse the chemical composition of the atmospheres of different comets, using a technique known as spectroscopy.

They said comets often act as “fossils” for astronomers because these objects formed “around 4.6 billion years ago, in the very young Solar System, and haven’t changed since that time”.

The researchers found iron and nickel atoms in the atmospheres of several comets within the Solar System.

They also discovered nickel vapours within the atmosphere of the icy interstellar comet 2I/Borisov – which was observed some 300 million kilometres away from the Sun (about twice the distance between the Earth and the Sun).

In solid form, heavy metals such as nickel and iron usually exist in the rocky interiors of comets, but in gaseous or vapour form, these substances are usually associated with hot environments, such as in the atmospheres of evaporating comets passing too close to the Sun.

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Study author Piotr Guzik, from the Jagiellonian University in Poland, said: “At first we had a hard time believing that atomic nickel could really be present in 2I/Borisov that far from the Sun.

“It took numerous tests and checks before we could finally convince ourselves.”

The researchers said their findings hint at a shared unknown birthplace for the Solar System as well as 2I/Borisov.

Study co-author Michal Drahus, also from the Jagiellonian University, said: “All of a sudden we understood that gaseous nickel is present in cometary atmospheres in other corners of the (Milky Way) Galaxy.

“Now imagine that our Solar System’s comets have their true analogues in other planetary systems – how cool is that?”