Metal atoms have been surprisingly discovered in the icy atmosphere of the first known interstellar comet to visit our solar system, according to a new study.
Astronomers have also detected metal in cold halos surrounding local solar system comets, suggesting that comets in our solar system and the interstellar visitor may have similar origins, the researchers add.
Comets, which are made up of dust and ice from planetary formation, could provide key clues to the chemistry of early planetary systems. Scientists often infer the makeup of comets by examining clouds of gas and dust called comas that surround the cores of comets.
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Scientists generally do not detect metals such as nickel in comas of comets, because their surfaces are usually too cold for the metal to vaporize. The exceptions to this rule are comets passing nearby or plunging into the sun, when temperatures can easily exceed the 800 degrees Fahrenheit (425 degrees Celsius) needed for nickel vapor to form.
Scientists have now detected nickel atoms in the coma of the first known interstellar comet, 2I / Borisov. First discovered in 2019, its speed and trajectory revealed that it was a rebel comet from interstellar space, making it the first known interstellar comet and the second known interstellar visitor after the rock. crepe-shaped 1I / ‘Oumuamua.
The discovery was unexpected – when astronomers first saw these nickel atoms in January using the Very Large Telescope in Chile, 2I / Borisov was far from the sun, with an estimated temperature of minus 135 degrees F (minus 93 degrees C). They detailed their findings in the May 20 issue of the journal Nature.
In an independent study also published in the May 20 issue of Nature, astronomers discovered gaseous nickel and iron in the cold comas of about 20 different types of solar system comets. The wavelengths of light from these metals that they detected using the Very Large Telescope were hidden in plain sight, mixed with the light spectrum of other molecules in coma.
The quantity of iron and the nickel that these comets released was small – only about 1 gram per second, up from about 220 pounds. (100 kilograms) of water per second produced by comets. Coincidentally, the amount of nickel these comets each produced per second was almost exactly the nickel content of an American nickel, or nickel.
“Usually, there is 10 times more iron than nickel, and in these cometary atmospheres, we found roughly the same amount for both elements”, Damien Hutsemékers, researcher at the University of Liège and co-author of the study, said in a press release. “We came to the conclusion that they could come from a special type of material on the surface of the comet’s nucleus, sublimating at a rather low temperature and releasing iron and nickel in roughly the same proportions. “
As to why astronomers neglected the metallic atoms in these cometary atmospheres even though the light spectra of many of them were visible over the past 20 years, “probably, so far, none of the observers who have seen these spectral signatures of nickel or iron could not even imagine that gaseous metals could be present in such a cold environment and left them unidentified, ”Piotr Guzik, astronomer at Jagiellonian University in Krakow, told Space.com, in Poland, who co-authored the 2I / Borisov study.
It is still not clear how all of these comets can generate metal at such cold temperatures. One possibility is that ultraviolet light from the sun could break down molecules containing nickel in comets.
Overall, “the fact that even such a minor constituent as nickel is present both in the coma of interstellar comet Borisov and in comets observed in the solar system suggests similar conditions at the time and place of their birth, “Guzik said.
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