Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua)

Abstract

‘Oumuamua (1I/2017 U1) is the first known object of interstellar origin to have entered the Solar System on an unbound and hyperbolic trajectory with respect to the Sun1. Various physical observations collected during its visit to the Solar System showed that it has an unusually elongated shape and a tumbling rotation state1,2,3,4 and that the physical properties of its surface resemble those of cometary nuclei5,6, even though it showed no evidence of cometary activity1,5,7. The motion of all celestial bodies is governed mostly by gravity, but the trajectories of comets can also be affected by non-gravitational forces due to cometary outgassing8. Because non-gravitational accelerations are at least three to four orders of magnitude weaker than gravitational acceleration, the detection of any deviation from a purely gravity-driven trajectory requires high-quality astrometry over a long arc. As a result, non-gravitational effects have been measured on only a limited subset of the small-body population9. Here we report the detection, at 30σ significance, of non-gravitational acceleration in the motion of ‘Oumuamua. We analyse imaging data from extensive observations by ground-based and orbiting facilities. This analysis rules out systematic biases and shows that all astrometric data can be described once a non-gravitational component representing a heliocentric radial acceleration proportional to r−2 or r−1 (where r is the heliocentric distance) is included in the model. After ruling out solar-radiation pressure, drag- and friction-like forces, interaction with solar wind for a highly magnetized object, and geometric effects originating from ‘Oumuamua potentially being composed of several spatially separated bodies or having a pronounced offset between its photocentre and centre of mass, we find comet-like outgassing to be a physically viable explanation, provided that ‘Oumuamua has thermal properties similar to comets.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Deep stacked images for dust detection.
Fig. 2: Astrometric residuals of ‘Oumuamua observations.

References

  1. 1.

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

    Article  PubMed  ADS  CAS  Google Scholar 

  2. 2.

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

    Article  ADS  Google Scholar 

  3. 3.

    Drahus, M. et al. Tumbling motion of 1I/‘Oumuamua reveals body’s violent past. Nature Astron. 2, 407–412 (2018).

    Article  ADS  Google Scholar 

  4. 4.

    Belton, M. J. S. et al. The excited spin state of 1I/2017 U1 ‘Oumuamua. Astrophys. J. 856, L21 (2018).

    Article  ADS  Google Scholar 

  5. 5.

    Fitzsimmons, A. et al. Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua. Nature Astron 2, 133–137 (2018).

    Article  ADS  Google Scholar 

  6. 6.

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

    Article  ADS  Google Scholar 

  7. 7.

    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. 851, L5 (2017).

    Article  ADS  Google Scholar 

  8. 8.

    Marsden, B. G., Sekanina, Z. & Yeomans, D. K. Comets and nongravitational forces. V. Astron. J. 78, 211–225 (1973).

    Article  ADS  Google Scholar 

  9. 9.

    Królikowska, M. Long-period comets with non-gravitational effects. Astron. Astrophys. 427, 1117–1126 (2004).

    Article  MATH  ADS  Google Scholar 

  10. 10.

    Wainscoat, R. et al. The Pan-STARRS search for near earth objects. Proc. IAU 10, 293–298 (2015).

    Article  Google Scholar 

  11. 11.

    Denneau, L. et al. The Pan-STARRS moving object processing system. Publ. Astron. Soc. Pacif. 125, 357–395 (2013).

    Article  ADS  Google Scholar 

  12. 12.

    Williams, G.V. MPEC 2017-U181: comet C/2017 U1 (PANSTARRS). IAU Minor Planet Center https://minorplanetcenter.net/mpec/K17/K17UI1.html (2017).

  13. 13.

    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 

  14. 14.

    Farnocchia, D., Chesley, S. R., Milani, A., Gronchi, G. F. & Chodas, P. W. in Asteroids IV (eds Michel, P. et al.) 815–834 (Univ. Arizona Press, Tuscan, 2015).

  15. 15.

    Prialnik, D. Modeling the comet nucleus interior. Earth Moon Planets 89, 27–52 (2000).

    Article  ADS  CAS  Google Scholar 

  16. 16.

    Park, R. S., Pisano, D. J., Lazio, T. J. W., Chodas, P. W. & Naidu, S. P. Search for OH 18-cm radio emission from 1I/2017 U1 with the Green Bank Telescope. Astron. J. 155, 185 (2018).

    Article  ADS  Google Scholar 

  17. 17.

    Cochran, A. L., Barker, E. S. & Gray, C. L. Thirty years of cometary spectroscopy from McDonald Observatory. Icarus 218, 144–168 (2012).

    Article  ADS  CAS  Google Scholar 

  18. 18.

    Fink, U. A taxonomic survey of comet composition 1985–2004 using CCD spectroscopy. Icarus 201, 311–334 (2009).

    Article  ADS  CAS  Google Scholar 

  19. 19.

    McNeill, A., Trilling, D. E. & Mommert, M. Constraints on the density and internal strength of 1I/‘Oumuamua. Astrophys. J. 857, L1 (2018).

    Article  ADS  Google Scholar 

  20. 20.

    Williams, G.V. MPEC 2008-D12: 2006 RH120. IAU Minor Planet Center https://minorplanetcenter.net/mpec/K08/K08D12.html (2008).

  21. 21.

    Micheli, M., Tholen, D. J. & Elliott, G. T. Detection of radiation pressure acting on 2009 BD. New Astron. 17, 446–452 (2012).

    Article  ADS  Google Scholar 

  22. 22.

    Micheli, M., Tholen, D. J. & Elliott, G. T. 2012 LA, an optimal astrometric target for radiation pressure detection. Icarus 226, 251–255 (2013).

    Article  ADS  Google Scholar 

  23. 23.

    Micheli, M., Tholen, D. J. & Elliott, G. T. Radiation pressure detection and density estimate for 2011 MD. Astrophys. J. 788, L1 (2014).

    Article  ADS  Google Scholar 

  24. 24.

    Vokrouhlický, D., Bottke, W. F., Chesley, S. R., Scheeres, D. J. & Statler, T. S. in Asteroids IV (eds Michel, P. et al.) 509–531 (Univ. Arizona Press, Tuscan, 2015).

  25. 25.

    Meyer-Vernet, N. Basics of the Solar Wind 348–351, 366–371 (Cambridge Univ. Press, Cambridge, 2007).

    Google Scholar 

  26. 26.

    Zubrin, R. M. & Andrews, D. G. Magnetic Sails and Interplanetary Travel. J. Spacecr. Rockets 28, 197–203 (1991).

    Article  ADS  Google Scholar 

  27. 27.

    Wang-Sheeley-Arge (WSA)-Enlil Solar Wind Prediction. Space Weather Prediction Center https://www.ngdc.noaa.gov/enlil/ (accessed March 2018).

  28. 28.

    Richter, I. et al. Magnetic field measurements during the ROSETTA flyby at asteroid (21) Lutetia. Planet. Space Sci. 66, 155–164 (2012).

    Article  ADS  Google Scholar 

  29. 29.

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

    Article  PubMed  PubMed Central  ADS  Google Scholar 

  30. 30.

    Yabushita, S. On the effect of non-gravitational processes on the dynamics of nearly parabolic comets. Mon. Not. R. Astron. Soc. 283, 347–352 (1996).

    Article  ADS  CAS  Google Scholar 

  31. 31.

    Krist, J. E., Hook, R. N. & Stoehr, F. 20 years of Hubble Space Telescope optical modeling using Tiny Tim. Proc. SPIE 8127, 81270J (2011).

    Article  ADS  Google Scholar 

  32. 32.

    Hastings, W. K. Monte Carlo sampling methods using Markov chains and their applications. Biometrika 57, 97–109 (1970).

    MathSciNet  Article  MATH  Google Scholar 

  33. 33.

    Gaia Collaboration. Gaia data release 2. Summary of the contents and survey properties. Astron. Astrophys. https://doi.org/10.1051/0004-6361/201833051 (2018).

  34. 34.

    Lindegren, L. et al. Gaia data release 1. Astrometry: one billion positions, two million proper motions and parallaxes. Astron. Astrophys. 595, A4 (2016).

    Article  Google Scholar 

  35. 35.

    Farnocchia, D., Chesley, S. R., Chamberlin, A. B. & Tholen, D. J. Star catalog position and proper motion corrections in asteroid astrometry. Icarus 245, 94–111 (2015).

    Article  ADS  Google Scholar 

  36. 36.

    Monet, D. G. et al. The USNO-B catalog. Astron. J. 125, 984–993 (2003).

    Article  ADS  Google Scholar 

  37. 37.

    Farnocchia, D. et al. High precision comet trajectory estimates: the Mars flyby of C/2013 A1 (Siding Spring). Icarus 266, 279–287 (2016).

    Article  ADS  Google Scholar 

  38. 38.

    Yeomans, D. K. & Chodas, P. W. An asymmetric outgassing model for cometary nongravitational accelerations. Astron. J. 98, 1083–1093 (1989).

    Article  ADS  Google Scholar 

  39. 39.

    A’Hearn, M. F. Comets as building blocks. Annu. Rev. Astron. Astrophys. 49, 281–299 (2011).

    Article  ADS  Google Scholar 

  40. 40.

    Carry, B. Density of asteroids. Planet. Space Sci. 73, 98–118 (2012).

    Article  ADS  Google Scholar 

  41. 41.

    Crovisier, J. & Schloerb, F. P. in Comets in the Post-Halley Era (eds Newburn, R. L. et al.) 166 (Kluwer, The Netherlands, 1991).

  42. 42.

    Schorghofer, N. The lifetime of ice on main belt asteroids. Astrophys. J. 682, 697–705 (2008).

    Article  ADS  Google Scholar 

  43. 43.

    Laufer, D., Pat-El, I. & Bar-Nun, A. Experimental simulation of the formation of non-circular active depressions on comet Wild-2 and of ice grain ejection from cometary surfaces. Icarus 178, 248–252 (2005).

    Article  ADS  Google Scholar 

  44. 44.

    Stern, S. A. ISM-induced erosion and gas-dynamical drag in the Oort cloud. Icarus 84, 447–466 (1990).

    Article  ADS  Google Scholar 

  45. 45.

    Prialnik, D. Crystallization, sublimation, and gas release in the interior of a porous comet nucleus. Astrophys. J. 388, 196–202 (1992).

    Article  ADS  CAS  Google Scholar 

  46. 46.

    Vereš, P., Farnocchia, D., Chesley, S. R. & Chamberlin, A. B. Statistical analysis of astrometric errors for the most productive asteroid surveys. Icarus 296, 139–149 (2017).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

K.J.M., J.T.K. and J.V.K. acknowledge support through NSF awards AST1413736 and AST1617015, in addition to support for HST programmes GO/DD-15405 and -15447 provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555. R.J.W. and R.W. acknowledge support through NASA under grant NNX14AM74G issued to support Pan-STARRS1 through the SSO Near Earth Object Observation Program. D.F., P.W.C. and A.E.P. conducted this research at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We thank S. Sheppard for obtaining the Magellan observations, and E. J. Christensen, W. H. Ryan and M. Mommert for providing astrometric uncertainty information related to the Catalina Sky Survey, Magdalena Ridge Observatory and Discovery Channel Telescope observations of ‘Oumuamua. This work is based on observations obtained at CFHT, which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France and the University of Hawai‘i . It is based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 2100.C-5008(A) and in part on observations obtained under programme GS-2017B-DD-7 obtained at the Gemini Observatory, which is operated by AURA under cooperative agreement with the NSF on behalf of the Gemini partnership: NSF (United States), NRC (Canada), CONICYT (Chile), MINCYT (Argentina) and MCT (Brazil). This is work is also based on observations made with NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555. This work has made use of data from the ESA mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

Reviewer information

Nature thanks A. Fitzsimmons, M. Granvik and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

Affiliations

Authors

Contributions

M.M. discovered the non-gravitational acceleration and extracted the high-precision astrometry from most ground-based observations obtained by the team. D.F. performed the different fits and modelling of the non-gravitational acceleration. K.J.M. secured the HST time and designed the observation programme, computed sublimation dust and gas outgassing limits, and provided the assessment of outgassing. M.W.B. led the design of the HST observations and contributed precision astrometry from HST images. O.R.H. obtained the deep stack of images, searched them for dust and companion, and estimated production rates. D.P. performed the thermal sublimation modelling. N.S. conducted thermal model calculations. H.A.W. managed the HST observations and the initial reduction of images. P.W.C. provided support in analysing possible explanations for the observed non-gravitational acceleration. J.T.K. assembled the deep stack of CFHT data to search for dust and outgassing. R.W. identified and searched pre-discovery images of ‘Oumuamua in Pan-STARRS1 data. R.J.W. obtained the observations using CFHT and searched for pre-discovery observations of ‘Oumuamua. H.E. contributed to the HST proposal and to the design of the HST observations. J.V.K. and K.C.C. contributed to the HST proposal. D.K. provided support in analysing possible explanations for the observed non-gravitational acceleration. A.E.P. investigated the magnetic hypothesis.

Corresponding author

Correspondence to Marco Micheli.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

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 Non-gravitational accelerations of Solar System comets and ‘Oumuamua.

Measured non-gravitational radial accelerations A1 for short-period (red) and long-period (blue) comets from the JPL Small Body Database (https://ssd.jpl.nasa.gov/sbdb.cgi). The solid vertical black line indicates the A1 value for ‘Oumuamua, which falls within the range observed for Solar System comets; the dashed vertical black lines mark the corresponding 1σ uncertainty. Source Data

Extended Data Table 1 Ground-based astrometry
Extended Data Table 2 HST astrometry
Extended Data Table 3 Uncertainty assumptions for existing astrometry

Source Data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Micheli, M., Farnocchia, D., Meech, K.J. et al. Non-gravitational acceleration in the trajectory of 1I/2017 U1 (‘Oumuamua). Nature 559, 223–226 (2018). https://doi.org/10.1038/s41586-018-0254-4

Download citation

Further reading

Comments

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.

Search

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