Abstract

The discovery1 of 1I/2017 U1 (1I/‘Oumuamua) has provided the first glimpse of a planetesimal born in another planetary system. This interloper exhibits a variable colour within a range that is broadly consistent with local small bodies, such as the P- and D-type asteroids, Jupiter Trojans and dynamically excited Kuiper belt objects2,3,4,5,6,7. 1I/‘Oumuamua appears unusually elongated in shape, with an axial ratio exceeding 5:1 (refs 1,4,5,8). Rotation period estimates are inconsistent and varied, with reported values between 6.9 and 8.3 h (refs 4,5,6,9). Here, we analyse all the available optical photometry data reported to date. No single rotation period can explain the exhibited brightness variations. Rather, 1I/‘Oumuamua appears to be in an excited rotational state undergoing non-principal axis rotation, or tumbling. A satisfactory solution has apparent lightcurve frequencies of 0.135 and 0.126 h−1 and implies a longest-to-shortest axis ratio of 5:1, although the available data are insufficient to uniquely constrain the true frequencies and shape. Assuming a body that responds to non-principal axis rotation in a similar manner to Solar System asteroids and comets, the timescale to damp 1I/‘Oumuamua’s tumbling is at least one billion years. 1I/‘Oumuamua was probably set tumbling within its parent planetary system and will remain tumbling well after it has left ours.

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References

  1. 1.

    Meech, K. J., Weryk, R. & Micheli, M. A brief visit from a red and extremely elongated interstellar asteroid. Nature 552, 378–381 (2017).

  2. 2.

    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. 851, L5 (2017).

  3. 3.

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

  4. 4.

    Bannister, M. T. et al. Col-OSSOS: colors of the interstellar planetesimal 1I/‘Oumuamua. Astrophys. J. Lett. 851, L38 (2017).

  5. 5.

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

  6. 6.

    Bolin, B. T. et al. APO time-resolved color photometry of highly elongated interstellar object 1I/‘Oumuamua. Astrophys. J. Lett. 852, L2 (2018).

  7. 7.

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

  8. 8.

    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. 851, L31 (2017).

  9. 9.

    Feng, F. & Jones, H. R. A. ‘Oumuamua as a messenger from the Local Association. Astrophys. J. Lett. 852, L27 (2018).

  10. 10.

    Drahus, M. et al. Tumbling motion of 1I/‘Oumuamua reveals body’s violent past. Preprint at https://arxiv.org/abs/1712.00437 (2017).

  11. 11.

    Pravec, P. et al. Tumbling asteroids. Icarus 173, 108–131 (2005).

  12. 12.

    Gutiérrez, P. J., Davidsson, B. J. R., Ortiz, J. L., Rodrigo, R. & Vidal-Nuñez, M. J. Comments on the amplitude–phase relationship of asteroid lightcurves. Effects of topography, surface scattering properties, and obliquity. Astron. Astrophys. 454, 367–377 (2006).

  13. 13.

    Zappala, V., Cellino, A., Barucci, A. M., Fulchignoni, M. & Lupishko, D. F. An analysis of the amplitude–phase relationship among asteroids. Astron. Astrophys. 231, 548–560 (1990).

  14. 14.

    Henych, T. & Pravec, P. Asteroid rotation excitation by subcatastrophic impacts. Mon. Not. R. Astron. Soc. 432, 1623–1631 (2013).

  15. 15.

    Scheeres, D. J., Ostro, S. J., Werner, R. A., Asphaug, E. & Hudson, R. S. Effects of gravitational interactions on asteroid spin states. Icarus 147, 106–118 (2000).

  16. 16.

    Samarasinha, N. H. & Mueller, B. E. A. Relating changes in cometary rotation to activity: current status and applications to Comet C/2012 S1 (ISON). Astrophys. J. Lett. 775, L10 (2013).

  17. 17.

    Vokrouhlický, D., Breiter, S., Nesvorný, D. & Bottke, W. F. Generalized YORP evolution: onset of tumbling and new asymptotic states. Icarus 191, 636–650 (2007).

  18. 18.

    Burns, J. A. & Safronov, V. S. Asteroid nutation angles. Mon. Not. R. Astron. Soc. 165, 403 (1973).

  19. 19.

    Sharma, I., Burns, J. A. & Hui, C.-Y. Nutational damping times in solids of revolution. Mon. Not. R. Astron. Soc. 359, 79–92 (2005).

  20. 20.

    Breiter, S., RoŻek, A. & Vokrouhlický, D. Stress field and spin axis relaxation for inelastic triaxial ellipsoids. Mon. Not. R. Astron. Soc. 427, 755–769 (2012).

  21. 21.

    Pravec, P. et al. The tumbling spin state of (99942) Apophis. Icarus 233, 48–60 (2014).

  22. 22.

    Scheirich, P. et al. The shape and rotation of asteroid 2008 TC3. Meteorit. Planet. Sci. 45, 1804–1811 (2010).

  23. 23.

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

  24. 24.

    Trilling, D. E. et al. Implications for planetary system formation from interstellar object 1I/2017 U1 (‘Oumuamua). Astrophys. J. Lett. 850, L38 (2017).

  25. 25.

    Grav, T. et al. The Pan-STARRS synthetic solar system model: a tool for testing and efficiency determination of the moving object processing system. Publ. Astron. Soc. Pac. 123, 423–447 (2011).

  26. 26.

    Lacerda, P., Jewitt, D. & Peixinho, N. High-precision photometry of Extreme KBO 2003 EL61. Astron. J. 135, 1749–1756 (2008).

  27. 27.

    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).

  28. 28.

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

  29. 29.

    Fukugita, M. et al. The Sloan Digital Sky Survey photometric system. Astron. J. 111, 1748 (1996).

  30. 30.

    Fraser, W. et al. TRIPPy: Trailed Image Photometry in Python. Astron. J. 151, 158 (2016).

  31. 31.

    Harris, A. W. Tumbling asteroids. Icarus 107, 209 (1994).

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Acknowledgements

W.C.F., A.F., M.T.B. and P.L. acknowledge support from Science and Technology Facilities Council grant ST/P0003094/1. M.T.B. also acknowledges support from Science and Technology Facilities Council grant ST/L000709/1. The work by P.P. was supported by the Grant Agency of the Czech Republic (grant 17-00774S). C.S. is supported by a Science and Technology Facilities Council Ernest Rutherford Fellowship and grant ST/L004569/1.

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Affiliations

  1. Astrophysics Research Centre, Queen’s University Belfast, Belfast, UK

    • Wesley C. Fraser
    • , Alan Fitzsimmons
    • , Pedro Lacerda
    •  & Michele T. Bannister
  2. Astronomical Institute, Academy of Sciences of the Czech Republic, Ondřejov, Czech Republic

    • Petr Pravec
  3. Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, UK

    • Colin Snodgrass
  4. Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Belgrade, Serbia

    • Igor Smolić

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Contributions

W.C.F. compiled the common filter dataset, re-reduced observations where necessary and led the analysis and writing of the manuscript. P.P., P. L. and I.S. performed the lightcurve modelling and assisted with writing. A.F. calculated damping timescale estimates and assisted with writing the paper. M.T.B. and C.S. assisted with interpretation of the lightcurve results and writing the paper.

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The authors declare no competing financial interests.

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Correspondence to Wesley C. Fraser.

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https://doi.org/10.1038/s41550-018-0398-z