A new study by a Belgian team using data from the European Southern Observatory’s Very Large Telescope (ESO’s VLT) has shown that iron and nickel exist in the atmospheres of comets throughout our Solar System, even those far from the Sun.
A new study by a Belgian team using data from the European Southern Observatory’s Very Large Telescope (ESO’s VLT) has shown that iron and nickel exist in the atmospheres of comets throughout our Solar System, even those far from the Sun. A separate study by a Polish team, who also used ESO data, reported that nickel vapour is also present in the icy interstellar comet 2I/Borisov. This is the first time heavy metals, usually associated with hot environments, have been found in the cold atmospheres of distant comets.
“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," says Jean Manfroid from the University of Liège, Belgium, who lead the new study on Solar System comets published today in Nature.
Astronomers know that heavy metals exist in comets’ dusty and rocky interiors. But, because solid metals don’t usually “sublimate” (become gaseous) at low temperatures, they did not expect to find them in the atmospheres of cold comets that travel far from the Sun. Nickel and iron vapours have now even been detected in comets observed at more than 480 million kilometres from the Sun, more than three times the Earth-Sun distance.
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Image: The detection of the heavy metals iron (Fe) and nickel (Ni) in the fuzzy atmosphere of a comet are illustrated in this image, which features the spectrum of light of C/2016 R2 (PANSTARRS) on the top left superimposed to a real image of the comet taken with the SPECULOOS telescope at ESO's Paranal Observatory. Each white peak in the spectrum represents a different element, with those for iron and nickel indicated by blue and orange dashes, respectively. Spectra like these are possible thanks to the UVES instrument on ESO's VLT, a high-resolution spectrograph that spreads the line so much they can be individually identified. In addition, UVES remains sensitive down to wavelengths of 300nm. Most of the important iron and nickel lines appear at wavelengths of around 350nm, meaning that the capabilities of UVES were essential in making this discovery. (Credit: ESO/L. Calçada, SPECULOOS Team/E. Jehin, Manfroid et al.)
