Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov


On 31 August 2019, an interstellar comet was discovered as it passed through the Solar System (2I/Borisov). On the basis of initial imaging observations, 2I/Borisov seemed to be similar to ordinary Solar System comets1,2—an unexpected characteristic given the multiple peculiarities of the only known previous interstellar visitor, 1I/‘Oumuamua3,4,5,6. Spectroscopic investigations of 2I/Borisov identified the familiar cometary emissions from CN (refs. 7,8,9), C2 (ref. 10), O i (ref. 11), NH2 (ref. 12), OH (ref. 13), HCN (ref. 14) and CO (refs. 14,15), revealing a composition similar to that of carbon monoxide-rich Solar System comets. At temperatures greater than 700 kelvin, comets also show metallic vapours that are produced by the sublimation of metal-rich dust grains16. Observation of gaseous metals had until very recently17 been limited to bright sunskirting and sungrazing comets18,19,20 and giant star-plunging exocomets21. Here we report spectroscopic observations of atomic nickel vapour in the cold coma of 2I/Borisov at a heliocentric distance of 2.322 astronomical units—equivalent to an equilibrium temperature of 180 kelvin. Nickel in 2I/Borisov seems to originate from a short-lived nickel-containing molecule with a lifetime of \({340}_{-200}^{+260}\) seconds at 1 astronomical unit and is produced at a rate of 0.9 ± 0.3 × 1022 atoms per second, or 0.002 per cent relative to OH and 0.3 per cent relative to CN. The detection of gas-phase nickel in the coma of 2I/Borisov is in line with the recent identification of this atom—as well as iron—in the cold comae of Solar System comets17.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Emission lines from gaseous atomic nickel in the near-UV spectrum of 2I/Borisov.
Fig. 2: Observed and modelled spatial profiles of nickel emission.
Fig. 3: Haser scalelengths of the observed nickel emission.

Data availability

The X-shooter raw data are available in the ESO archive at https://archive.eso.orgSource data are provided with this paper.

Code availability

The EsoReflex pipeline is available from the ESO website at All custom codes are direct implementations of standard methods and techniques, described in detail in Methods.


  1. Guzik, P. et al. Initial characterization of interstellar comet 2I/Borisov. Nat. Astron. 4, 53–57 (2020).

    Article  ADS  Google Scholar 

  2. Jewitt, D. & Luu, J. Initial characterization of interstellar comet 2I/2019 Q4 (Borisov). Astrophys. J. Lett. 886, 29 (2019).

  3. Fraser, W. C. et al. The tumbling rotational state of 1I/‘Oumuamua. Nat. Astron. 2, 383–386 (2018).

    Article  ADS  Google Scholar 

  4. Meech, K. J. et al. A brief visit from a red and extremely elongated interstellar asteroid. Nature 552, 378–381 (2017).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  5. Drahus, M. et al. Tumbling motion of 1I/‘Oumuamua and its implications for the body’s distant past. Nat. Astron. 2, 407–412 (2018).

    Article  ADS  Google Scholar 

  6. Micheli, M. et al. Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua). Nature 559, 223–226 (2018).

    Article  ADS  CAS  PubMed  Google Scholar 

  7. Fitzsimmons, A. et al. Detection of CN gas in interstellar object 2I/Borisov. Astrophys. J. 885, L9 (2019).

    Article  ADS  CAS  Google Scholar 

  8. De León, J. et al. Visible and near-infrared observations of interstellar comet 2I/Borisov with the 10.4-m GTC and the 3.6-m TNG telescopes. Mon. Not. R. Astron. Soc. 495, 2053–2062 (2020).

    Article  ADS  Google Scholar 

  9. Kareta, T. et al. Carbon chain depletion of 2I/Borisov. Astrophys. J. 889, L38 (2020).

    Article  ADS  CAS  Google Scholar 

  10. Lin, H. W. et al. Detection of diatomic carbon in 2I/Borisov. Astrophys. J. 889, L30 (2020).

    Article  ADS  CAS  Google Scholar 

  11. McKay, A. J., Cochran, A. L., Dello Russo, N. & DiSanti, M. A. Detection of a water tracer in interstellar comet 2I/Borisov. Astrophys. J. 889, L10 (2020).

    Article  ADS  CAS  Google Scholar 

  12. Bannister, M. T. et al. Interstellar comet 2I/Borisov as seen by MUSE: C2, NH2 and red CN detections. Preprint at (2020).

  13. Jehin, E. et al. CBET 4719: COMET 2I/2019 Q4. (2020).

  14. Cordiner, M. A. et al. Unusually high CO abundance of the first active interstellar comet. Nat. Astron. 4, 861–866 (2020).

    Article  ADS  Google Scholar 

  15. Bodewits, D. et al. The carbon monoxide-rich interstellar comet 2I/Borisov. Nat. Astron. 4, 867–871 (2020).

    Article  ADS  Google Scholar 

  16. Feldman, P., Cochran, A. & Combi, M. in Comets II (eds Festou, M., Keller, H. U. & Weaver, H. A.) 425–447 (Univ. Arizona Press, 2004).

  17. Manfroid, J., Hutsemékers, D. & Jehin, E. Iron and nickel atoms in cometary atmospheres even far from the Sun. Nature (2021).

  18. Preston, G. The spectrum of comet Ikeya-Seki (1965f). Astrophys. J. 147, 718–742 (1967).

    Article  ADS  CAS  Google Scholar 

  19. Slaughter, C. The emission spectrum of comet Ikeya-Seki 1965-f at perihelion passage. Astron. J. 74, 929–943 (1969).

    Article  ADS  Google Scholar 

  20. Fulle, M. et al. Discovery of the atomic iron tail of comet McNaught using the heliospheric imager on STEREO. Astrophys. J. 661, L93 (2007).

    Article  ADS  CAS  Google Scholar 

  21. Kiefer, F. et al. Fe I in the β Pictoris circumstellar gas disk. II. Time variations in the iron circumstellar gas. Astron. Astrophys. 621, A58 (2019).

    Article  CAS  Google Scholar 

  22. Kim, S. J., A’Hearn, M. F., Wellnitz, D. D., Meier, R. & Lee, Y. S. The rotational structure of the B–X system of sulfur dimers in the spectra of Comet Hyakutake (C/1996 B2). Icarus 166, 157–166 (2003).

  23. Valk, J. H. & O’Dell, C. R. Near-ultraviolet spectroscopy of comet Austin (1989c1). Astrophys. J. 388, 621–632 (1992).

    Article  ADS  CAS  Google Scholar 

  24. Cochran, A. L. A search for N2+ in spectra of comet C/2002 C1 (Ikeya-Zhang). Astrophys. J. 576, L165–L168 (2002).

    Article  ADS  CAS  Google Scholar 

  25. Cochran, A. L. & McKay, A. J. Strong CO+ and N2+ emission in comet C/2016 R2 (Pan-STARRS). Astrophys. J. Lett. 854, L10 (2018).

    Article  ADS  Google Scholar 

  26. Opitom, C. et al. High resolution optical spectroscopy of the N2-rich comet C/2016 R2 (PanSTARRS). Astron. Astrophys. 624, A64 (2019).

    Article  CAS  Google Scholar 

  27. Swings, P. Complex structure of cometary bands tentatively ascribed to the contour of the solar spectrum. Lick Obs. Bull. 19, 131 (1941).

    ADS  CAS  Google Scholar 

  28. Peck, E. R. & Reeder, K. Dispersion of air. J. Opt. Soc. Am. 62, 958–962 (1972).

  29. Haser, L. Distribution d’intensité dans la tête d’une comète. Bull. Acad. R. Sci. Liege 43, 740–750 (1957).

    ADS  MathSciNet  MATH  Google Scholar 

  30. Combi, M. R., Harris, W. M. & Skyth, W. M. in Comets II (eds Festou, M., Keller, H. U. & Weaver, H. A.) 523–554 (Univ. Arizona Press, 2004).

  31. Huebner, W. F. & Mukherjee, J. Photoionization and photodissociation rates in solar and blackbody radiation fields. Planet. Space Sci. 106, 11–45 (2015).

    Article  ADS  CAS  Google Scholar 

  32. A’Hearn, M. F., Millis, R. C., Schleicher, D. G., Osip, D. J. & Birch, P. V. The ensemble properties of comets: results from narrowband photometry of 85 comets, 1976–1992. Icarus 118, 223–270 (1995).

    Article  ADS  Google Scholar 

  33. Johnson, J. A. Populating the periodic table: nucleosynthesis of the elements. Science 363, 474–478 (2019).

    Article  ADS  CAS  PubMed  Google Scholar 

  34. Wasson, J. T. Meteorites 11–38 (Springer, 1974).

  35. Goldberg, R. A. & Aikin, A. C. Comet Encke: meteor metallic ion identification by mass spectrometer. Science 180, 294–296 (1973).

    Article  ADS  CAS  PubMed  Google Scholar 

  36. Jessberger, E. K., Christoforidis, A. & Kissel, J. Aspects of the major element composition of Halley’s dust. Nature 332, 691–695 (1988).

    Article  ADS  CAS  Google Scholar 

  37. Flynn, G. J. et al. Elemental compositions of comet 81P/Wild 2 samples collected by Stardust. Science 314, 1731–1735 (2006).

    Article  ADS  CAS  PubMed  Google Scholar 

  38. Zolensky, M. E. et al. Mineralogy and petrology of comet 81P/Wild 2 nucleus samples. Science 314, 1735–1739 (2006).

    Article  ADS  CAS  PubMed  Google Scholar 

  39. Chochol, D., Rušín, V., Kulčár, L. & Vanýsek, V. Emission features in the solar corona after the perihelion passage of Comet 1979 XI. Astrophys. Space Sci. 91, 71–77 (1983).

    Article  ADS  CAS  Google Scholar 

  40. Hoeijmakers, H. J. et al. Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b. Nature 560, 453–455 (2018).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  41. Hoeijmakers, H. J. et al. Hot exoplanet atmospheres resolved with transit spectroscopy (HEARTS). Astron. Astrophys. 641, A123 (2020).

    Article  CAS  Google Scholar 

  42. Vanderburg, A. et al. A disintegrating minor planet transiting a white dwarf. Nature 526, 546–549 (2015).

    Article  ADS  CAS  PubMed  Google Scholar 

  43. Xu, S. et al. The chemical composition of an extrasolar Kuiper-belt-object. Astrophys. J. Lett. 836, L7 (2017).

    Article  ADS  Google Scholar 

  44. Prialnik, D., Benkhoff, J. & Podolak, M. in Comets II (eds Festou, M., Keller, H. U. & Weaver, H. A.) 359–387 (Univ. Arizona Press, 2004).

  45. Rubin, M. et al. Elemental and molecular abundances in comet 67P/Churyumov–Gerasimenko. Mon. Not. R. Astron. Soc. 489, 594–607 (2019).

    Article  ADS  CAS  Google Scholar 

  46. Ivezić, Ž., et al. LSST: from science drivers to reference design and anticipated data products. Astrophys. J. 873, 111 (2019).

    Article  ADS  Google Scholar 

  47. Freudling, W. et al. Automated data reduction workflows for astronomy. The ESO Reflex environment. Astron. Astrophys. 559, A96 (2013).

    Article  Google Scholar 

  48. Kurucz, R. L. New atlases for solar flux, irradiance, central intensity, and limb intensity. Mem. Soc. Astron. Ital. 8, 189 (2005).

    ADS  Google Scholar 

  49. Kramida, A., Ralchenko, Yu., Reader, J. & NIST ASD Team. NIST Atomic Spectra Database (v.5.7.1) (National Institute of Standards and Technology, accessed 22 October 2020);

  50. Haser, L., Oset, S. & Bodewits, D. Intensity distribution in the heads of comets. Planet. Sci. J. 1, 83 (2020).

    Article  Google Scholar 

  51. Combi, M. R. & Delsemme, A. H. Neutral cometary atmospheres. I—An average random walk model for photodissociation in comets. Astrophys. J. 237, 633–640 (1980).

    Article  ADS  CAS  Google Scholar 

  52. Schleicher, D. G. & A’Hearn, M. F. The fluorescence of cometary OH. Astrophys. J. 331, 1058–1077 (1988).

    Article  ADS  CAS  Google Scholar 

  53. Schleicher, D. G. The fluorescence efficiencies of the CN violet bands in comets. Astron. J. 140, 973–984 (2010).

    Article  ADS  CAS  Google Scholar 

  54. Bohlin, R. C., Gordon, K. D. & Tremblay P.-E. Techniques and review of absolute flux calibration from the ultraviolet to the mid-infrared. Publ. Astron. Soc. Pac. 126, 711 (2014).

  55. Hall, L. A. & Anderson, G. P. High-resolution solar spectrum between 2000 and 3100 Å. J. Geophys. Res. 96, 12927 (1991).

Download references


We thank K. Rusek for help with proposal writing, M. Ratajczak and M. Gromadzki for introducing us to X-shooter data reduction, and P. Kozyra for discussion on nickel-containing molecules. This work is based on observations collected at the ESO under ESO programme 0104.C-0933(B). We thank the ESO staff for support. We are also grateful for support from the National Science Centre of Poland through ETIUDA scholarship no. 2020/36/T/ST9/00596 to P.G. and SONATA BIS grant no. 2016/22/E/ST9/00109 to M.D., and we acknowledge support from the Polish Ministry of Science and Higher Education through grant no. DIR/WK/2018/12.

Author information

Authors and Affiliations



P.G. and M.D. wrote the telescope time proposal, searched for the origin of the detected spectral lines and wrote the paper. P.G. prepared the observations, reduced and calibrated the data, identified the emitting species and measured the spectral lines. M.D. created the fluorescence model, retrieved the scalelengths and calculated the production rate.

Corresponding authors

Correspondence to Piotr Guzik or Michał Drahus.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Ryan Fortenberry and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Complete spectrum of comet 2I/Borisov from X-shooter UVB arm.

a, Flux-calibrated spectrum with fitted dust continuum (see Methods). b, Same as a but with the dust-continuum component removed. Major emission features are labelled. c, Modelled spectrum of nickel fluorescence emission (see Methods) scaled to best match the two brightest lines.

Extended Data Fig. 2 Distribution of Monte Carlo-simulated production rates.

The distribution was constructed from the production rates corresponding to the results of the Monte Carlo simulation in Fig. 3b (see Methods). Results are presented in three groups according to the assumed PSF equal to 0.65 (blue), 1.0 (red) and 1.5 (green) arcsec.

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Guzik, P., Drahus, M. Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov. Nature 593, 375–378 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing