Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua

Abstract

During the formation and evolution of the Solar System, significant numbers of cometary and asteroidal bodies were ejected into interstellar space1,2. It is reasonable to expect that the same happened for planetary systems other than our own. Detection of such interstellar objects would allow us to probe the planetesimal formation processes around other stars, possibly together with the effects of long-term exposure to the interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known interstellar object, discovered by the Pan-STARRS1 telescope in October 2017 (ref. 3). The discovery epoch photometry implies a highly elongated body with radii of ~ 200 × 20 m when a comet-like geometric albedo of 0.04 is assumed. The observable interstellar object population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity of 'Oumuamua implies a lack of surface ice. Here, we report spectroscopic characterization of ‘Oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer Solar System. We show that this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure4. An internal icy composition cannot therefore be ruled out by the lack of activity, even though ‘Oumuamua passed within 0.25 au of the Sun.

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Fig. 1: Optical reflectance spectra of 1I/2017 U1 obtained with the WHT + ACAM and VLT + X-shooter.
Fig. 2: WHT + ACAM (red data points) and VLT + X-shooter (grey data points) spectra of 1I/2017 U1 compared with reflectances of main-belt asteroids.
Fig. 3: Comparison of our X-shooter 1I/2017 U1 spectrum from Fig. 2 with ranges of reflectance spectra of outer Solar System bodies.
Fig. 4: Thermal modelling of 1I/2017 U1 during its flyby of the Sun, demonstrating the survivability of sub-surface ice.

References

  1. 1.

    Charnoz, S. & Morbidelli, A. Coupling dynamical and collisional evolution of small bodies: an application to the early ejection of planetesimals from the Jupiter–Saturn region. Icarus 166, 141–156 (2003).

    ADS  Article  Google Scholar 

  2. 2.

    Dones, L., Weissman, P. R., Levison, H. F. & Duncan, M. J. in Comets II (eds Festou, M. C., Keller, H. U. & Weaver, H. A.) 153–174 (Univ. Arizona Press, Tucson, 2004).

  3. 3.

    Meech, K. J. et al. A brief visit from a red and extremely elongated interstellar asteroid. Nature https://doi.org/10.1038/nature25020 (2017).

  4. 4.

    Guilbert-Lepoutre, A. et al. On the evolution of comets. Space Sci. Rev. 197, 271–296 (2015).

    ADS  Article  Google Scholar 

  5. 5.

    Fitzsimmons, A., Hyland, M., Jedicke, R., Snodgrass, C. & Yang, B. Minor planets 2017 SN_33 and 2017 U1. Cent. Bur. Electr. Telegr. 4450, 2 (2017).

    ADS  Google Scholar 

  6. 6.

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

  7. 7.

    Knight, M. M. et al. On the rotation period and shape of the hyperbolic asteroid 1I/`Oumuamua (2017) U1 from its lightcurve. Astrophys. J. Lett. (in the press); preprint at https://arxiv.org/abs/1711.01402.

  8. 8.

    Bannister, M. T. et al. Col-OSSOS: colors of the interstellar planetesimal 1I/`Oumuamua. Astrophys. J. Lett. (in the press); preprint at https://arxiv.org/abs/1711.06214.

  9. 9.

    Ye, Q.-Z., Zhang, Q., Kelley, M. S. P. & Brown, P. G. 1I/2017 U1 (`Oumuamua) is hot: imaging, spectroscopy and search of meteor activity. Astrophys. J. Lett. (in the press); preprint at https://arxiv.org/abs/1711.02320.

  10. 10.

    Rivkin, A. S. et al. in Asteroids IV (eds Michel, P., DeMeo, F. E. & Bottke, W. F.) 65–87 (Univ. Arizona Press, Tucson, 2015).

  11. 11.

    Reddy, V., Dunn, T. L., Thomas, C. A., Moskovitz, N. A. & Burbine, T. H. in Asteroids IV (eds Michel, P., DeMeo, F. E. & Bottke, W. F.) 43–63 (Univ. Arizona Press, Tucson, 2015).

  12. 12.

    Masiero, J. Palomar optical spectrum of hyperbolic near-earth object A/2017 U1. Preprint at https://arxiv.org/abs/1710.09977v2 (2017).

  13. 13.

    Bolin, B. T. et al. APO time resolved color photometry of highly-elongated interstellar object 1I/’Oumuamua. Astrophys. J. Lett. (in the press); preprint at https://arxiv.org/abs/1711.04927v4.

  14. 14.

    Jewitt, D. et al. Interstellar Interloper 1I/2017 U1: observations from the NOT and WIYN telescopes. Astrophys J. Lett. 850, L36 (2017).

  15. 15.

    Mothé-Diniz, T., Lazzaro, D., Carvano, J. M. & Florczak, M. Rotationally resolved spectra of some S-type asteroids. Icarus 148, 494–507 (2000).

    ADS  Article  Google Scholar 

  16. 16.

    Fraser, W. C., Brown, M. E. & Glass, F. The Hubble Wide Field Camera 3 test of surfaces in the outer solar system: spectral variation on Kuiper belt objects. Astrophys. J. 804, 31 (2015).

    ADS  Article  Google Scholar 

  17. 17.

    DeMeo, F. E., Binzel, R. P., Slivan, S. M. & Bus, S. J. An extension of the bus asteroid taxonomy into the near-infrared. Icarus 202, 160–180 (2009).

    ADS  Article  Google Scholar 

  18. 18.

    Emery, J. P., Burr, D. M. & Cruikshank, D. P. Near-infrared spectroscopy of trojan asteroids: evidence for two compositional groups. Astron. J. 141, 25 (2011).

    ADS  Article  Google Scholar 

  19. 19.

    Snodgrass, C. et al. Distant activity of 67P/Churyumov–Gerasimenko in 2014: ground-based results during the Rosetta pre-landing phase. Astron. Astrophys. 588, A80 (2016).

    Article  Google Scholar 

  20. 20.

    Merlin, F., Hromakina, T., Perna, D., Hong, M. J. & Alvarez-Candal, A. Taxonomy of trans-Neptunian objects and centaurs as seen from spectroscopy. Astron. Astrophys. 604, A86 (2017).

    ADS  Article  Google Scholar 

  21. 21.

    Pike, R. E. et al. Col-OSSOS: z-band photometry reveals three distinct TNO surface types. Astron. J. 154, 101 (2017).

    ADS  Article  Google Scholar 

  22. 22.

    Brunetto, R., Barucci, M. A., Dotto, E. & Strazzulla, G. Ion irradiation of frozen methanol, methane, and benzene: linking to the colors of centaurs and trans-Neptunian objects. Astrophys. J. 644, 646–650 (2006).

    ADS  Article  Google Scholar 

  23. 23.

    Strazzulla, G., Cooper, J. F., Christian, E. R. & Johnson, R. E. Irradiation ionique des OTNs: des flux mesurés dans l’espace aux expériences de laboratoire. C. R. Phys. 4, 791–801 (2003).

    ADS  Article  Google Scholar 

  24. 24.

    Meech, K. J. et al. Inner solar system material discovered in the Oort cloud. Sci. Adv. 2, e1600038 (2016).

    ADS  Article  Google Scholar 

  25. 25.

    Engelhardt, T. et al. An observational upper limit on the interstellar number density of asteroids and comets. Astron. J. 153, 133 (2017).

    ADS  Article  Google Scholar 

  26. 26.

    Jewitt, D. C. in Comets II (eds Festou, M. C., Keller, H. U. & Weaver, H. A.) 659–676 (Univ. Arizona Press, Tucson, 2004).

  27. 27.

    Groussin, O. et al. Gravitational slopes, geomorphology, and material strengths of the nucleus of comet 67P/Churyumov–Gerasimenko from OSIRIS observations. Astron. Astrophys. 583, A32 (2015).

    Article  Google Scholar 

  28. 28.

    Meech, K. J. et al. Activity of comets at large heliocentric distances pre-perihelion. Icarus 201, 719–739 (2009).

    ADS  Article  Google Scholar 

  29. 29.

    Zackrisson, E. et al. Terrestrial planets across space and time. Astrophys. J. 833, 214 (2016).

    ADS  Article  Google Scholar 

  30. 30.

    Jewitt, D. Color systematics of comets and related bodies. Astron. J. 150, 201 (2015). 1510.07069.

    ADS  Article  Google Scholar 

  31. 31.

    Benn, C., Dee, K. & Agócs, T. ACAM: a new imager/spectrograph for the William Herschel Telescope Proc. SPIE 7014, 70146X (2008); https://doi.org/10.1117/12.788694.

  32. 32.

    Vernet, J. et al. X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope. Astron. Astrophys. 536, A105 (2011).

    Article  Google Scholar 

  33. 33.

    Cruikshank, D. P. et al. The composition of centaur 5145 Pholus. Icarus 135, 389–407 (1998).

    ADS  Article  Google Scholar 

  34. 34.

    Doressoundiram, A. et al. Spectral characteristics and modeling of the trans-Neptunian object (55565) 2002 AW197 and the centaurs (55576) 2002 GB10 and (83982) 2002 GO9: ESO Large Program on TNOs and Centaurs. Plan. Space Sci. 53, 1501–1509 (2005).

    ADS  Article  Google Scholar 

  35. 35.

    Emery, J. P., Burr, D. M. & Cruikshank, D. P. Near-infrared spectroscopy of trojan asteroids: evidence for two compositional groups. Astron. J. 141, 25 (2011).

    ADS  Article  Google Scholar 

  36. 36.

    Capaccioni, F. et al. The organic-rich surface of comet 67P/Churyumov–Gerasimenko as seen by VIRTIS/Rosetta. Science 347, 628 (2015).

    Article  Google Scholar 

  37. 37.

    Soderblom, L. A. et al. Short-wavelength infrared (1.3-2.6 μm) observations of the nucleus of Comet 19P/Borrelly. Icarus 167, 100–112 (2004).

    ADS  Article  Google Scholar 

  38. 38.

    Abell, P. A. et al. Physical characteristics of comet nucleus C/2001 OG108 (LONEOS). Icarus 179, 174–194 (2005).

    ADS  Article  Google Scholar 

  39. 39.

    Delbo, M., Mueller, M., Emery, J. P., Rozitis, B. & Capria, M. T. in Asteroids IV (eds Michel, P., DeMeo, F. E. & Bottke, W. F.) 107–128 (Univ. Arizona Press, Tucson, 2015).

  40. 40.

    Rozitis, B. & Green, S. F. Directional characteristics of thermal-infrared beaming from atmosphereless planetary surfaces—a new thermophysical model. Mon. Not. R. Astron. Soc. 415, 2042–2062 (2011).

    ADS  Article  Google Scholar 

  41. 41.

    Fornasier, S. et al. Spectrophotometric properties of the nucleus of comet 67P/Churyumov–Gerasimenko from the OSIRIS instrument onboard the ROSETTA spacecraft. Astron. Astrophys. 583, A30 (2015).

    Article  Google Scholar 

  42. 42.

    Spohn, T. et al. Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov–Gerasimenko. Science 349, aab0464 (2015).

  43. 43.

    Lowry, S. et al. The nucleus of comet 67P/Churyumov–Gerasimenko. A new shape model and thermophysical analysis. Astron. Astrophys. 548, A12 (2012).

    Article  Google Scholar 

  44. 44.

    Groussin, O. et al. The temperature, thermal inertia, roughness and color of the nuclei of comets 103P/Hartley 2 and 9P/Tempel 1. Icarus 222, 580–594 (2013).

    ADS  Article  Google Scholar 

  45. 45.

    Gasc, S. et al. Change of outgassing pattern of 67P/Churyumov–Gerasimenko during the March 2016 equinox as seen by ROSINA. Mon. Not. R. Astron. Soc. 469, S108–S117 (2017).

    Article  Google Scholar 

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Acknowledgements

We thank the observatory staff at the Isaac Newton Group of Telescopes and the European Southern Observatory for responding quickly to our observing requests. Particular thanks go to R. Ashley, C. Fariña and I. Skillen (Isaac Newton Group) and G. Beccari, B. Haeussler and F. Labrana (European Southern Observatory). A.F., M.T.B. and W.C.F. acknowledge support from Science and Technology Facilities Council grant ST/P0003094/1 and M.T.B. acknowledges support from Science and Technology Facilities Council grant ST/L000709/1. C.S. acknowledges support from the Science and Technology Facilities Council in the form of an Ernest Rutherford Fellowship. B.R. is supported by a Royal Astronomical Society Research Fellowship. The WHT is operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The ACAM spectroscopy was obtained as part of programme SW2017b11. This paper is also based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under European Southern Observatory programme 2100.C-5009.

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A.F. led the application and organization of the WHT observations, analysis of these data and writing of the paper. C.S. led the application for VLT observations, organized the observing plan and assisted with analysis and writing. B.R. performed the thermal modelling of 1I/2017 U1. B.Y. was co-investigator on the telescope proposals, assisted in writing the VLT proposal and reduced the X-shooter data. M.T.B. and W.C.F. assisted in interpretation of the spectra in terms of known TNO properties and helped with writing the paper. M.H. reduced the WHT data. T.S. reduced the VLT data and provided the comparison spectrum of Echeclus. R.J. was co-investigator on the telescope proposals and contributed to the analysis and interpretation, especially with respect to observational selection effects. P.L. assisted in interpretation of the variable spectra and helped with writing the paper.

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Correspondence to Alan Fitzsimmons.

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Fitzsimmons, A., Snodgrass, C., Rozitis, B. et al. Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua. Nat Astron 2, 133–137 (2018). https://doi.org/10.1038/s41550-017-0361-4

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