Free Astronomy Magazine September-October 2021

31 SEPTEMBER-OCTOBER 2021 ASTRO PUBLISHING those lines in their archival data from other telescopes,” Jehin says. “We think this will also trigger new work on the subject.” Another remarkable study published in Nature shows that heavy metals are also present in the atmosphere of the interstellar comet 2I/Borisov. A team in Poland observed this ob- ject, the first alien comet to visit our Solar System, using the X-shooter spectrograph on ESO’s VLT when the comet flew by about a year and a half ago. They found that 2I/Bo- risov’s cold atmosphere contains gaseous nickel. “At first we had a hard time believ- ing 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,” says study au- thor Piotr Guzik from the Jagiellon- ian University in Poland. The finding is surprising because, before these two studies, gases with heavy metal atoms had only been observed in hot environments, such as in the at- mospheres of ultra-hot exoplanets or evaporating comets that passed too close to the Sun. 2I/Borisov was observed when it was some 300 million kilometres away from the Sun, or about twice the Earth-Sun distance. Studying interstellar bodies in detail is fundamental to science because they carry invaluable information about the alien planetary systems they originate from. “All of a sud- den we understood that gaseous nickel is present in cometary at- mospheres in other corners of the Galaxy,” says co-author Michał Dra- hus, also from the Jagiellonian Uni- versity. The Polish and Belgian studies show that 2I/Borisov and Solar System comets have even more in common than previously thought. “Now imagine that our Solar System’s comets have their true analogues in other planetary systems — how cool is that?” Drahus concludes. T his image was taken with the FORS2 in- strument on ESO’s Very Large Telescope in late 2019, when comet 2I/Borisov passed near the Sun. Since the comet was travelling at breakneck speed, around 175,000 kilome- tres per hour, the back- ground stars appeared as streaks of light as the telescope followed the comet’s trajectory. The colours in these streaks give the image some disco flair and are the result of combining observations in differ- ent wavelength bands, highlighted by the vari- ous colours in this com- posite image. [ESO/ O. Hainaut] the same amount of nickel. “Usually there is 10 times more iron than nickel, and in those comet atmos- pheres we found about the same quantity for both elements. We came to the conclusion they might come from a special kind of material on the surface of the comet nucleus, sublimating at a rather low temper- ature and releasing iron and nickel in about the same proportions,” ex- plains Damien Hutsemékers, also a member of the Belgian team from the University of Liège. Although the team aren’t sure yet what material this might be, ad- vances in astronomy — such as the Mid-infrared ELT Imager and Spec- trograph (METIS) on ESO’s upcoming Extremely Large Telescope (ELT) — will allow researchers to confirm the source of the iron and nickel atoms found in the atmospheres of these comets. The Belgian team hope their study will pave the way for future re- search. “Now people will search for !