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.

  • Letter
  • Published:

The tumbling rotational state of 1I/‘Oumuamua


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.

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

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: The geometry-reduced and colour-corrected r′-band photometry, Hr′, of 1I/‘Oumuamua cannot be well described by a model of simple rotation.
Fig. 2: Rotational colour variations.

Similar content being viewed by others


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

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

  3. Fitzsimmons, A. et al. Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua. Nat. Astron. (2018).

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  7. Masiero, J. Palomar optical spectrum of hyperbolic near-earth object A/2017 U1. Preprint at (2017).

  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).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  10. Drahus, M. et al. Tumbling motion of 1I/‘Oumuamua reveals body’s violent past. Preprint at (2017).

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

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

  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).

    ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  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).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

Download references


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.

Author information

Authors and Affiliations



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.

Corresponding author

Correspondence to Wesley C. Fraser.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

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

Supplementary information

Supplementary Information

Supplementary Table 1.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

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

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


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