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Earth’s Trojan asteroid

Naturevolume 475, pages481–483 (2011)Cite this article

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Abstract

It was realized in 1772 that small bodies can stably share the same orbit as a planet if they remain near ‘triangular points’ 60° ahead of or behind it in the orbit1. Such ‘Trojan asteroids’ have been found co-orbiting with Jupiter2, Mars3 and Neptune4. They have not hitherto been found associated with Earth, where the viewing geometry poses difficulties for their detection5, although other kinds of co-orbital asteroid (horseshoe orbiters6 and quasi-satellites7) have been observed8. Here we report an archival search of infrared data for possible Earth Trojans, producing the candidate 2010 TK7. We subsequently made optical observations which established that 2010 TK7 is a Trojan companion of Earth, librating around the leading Lagrange triangular point, L4. Its orbit is stable over at least ten thousand years.

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Figure 1:Orbital parameters of asteroid 2010 TK7.
Figure 2:Semimajor axis versus relative longitude for 2010 TK7.

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Acknowledgements

We thank the WISE team and JPL and NEODyS (University of Pisa) data services. Support came from Canada’s Natural Sciences and Engineering Research Council and Research Chairs. Problems with some 2010 TK7 positions reported in ref.23 were pointed out by T. Spahr and D. Tholen. We are grateful to them for data reductions provided, and to D. Tholen, M. Micheli and G. T. Elliot for observations made in support of this study.

Author information

Authors and Affiliations

  1. Athabasca University, 1 University Drive, Athabasca, Alberta T9S 3A3, Canada

    Martin Connors

  2. Department of Earth and Space Sciences, UCLA, Los Angeles, 90095, California, USA

    Martin Connors

  3. Department of Physics and Astronomy, The University of Western Ontario, London, Ontario N6A 3K7, Canada

    Paul Wiegert

  4. Canada–France–Hawaii Telescope, Kamuela, 96743, Hawaii, USA

    Christian Veillet

Authors
  1. Martin Connors

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  2. Paul Wiegert

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  3. Christian Veillet

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Contributions

The authors contributed equally to this work. M.C. and P.W. concentrated on dynamical calculations, and C.V. concentrated on observations and associated data reduction.

Corresponding author

Correspondence toMartin Connors.

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Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-2 with legends and the full legend for Supplementary Movie 1. (PDF 897 kb)

Supplementary Movie 1

This movie shows an artist's conception of the Sun, Earth and asteroid 2010 TK7 (right) as seen by an observer revolving around the Sun near the Earth (see Supplementary Information file for full legend). (MPG 6257 kb)

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Connors, M., Wiegert, P. & Veillet, C. Earth’s Trojan asteroid.Nature475, 481–483 (2011). https://doi.org/10.1038/nature10233

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Editorial Summary

Earth's travelling companion

More than 200 years ago, mathematician Joseph-Louis Lagrange predicted the existence of what became known as Trojan asteroids — small bodies that can stably share the orbit of a planet if they remain near 'triangular points' 60° ahead of or behind it in its orbit. Jupiter has thousands of Trojans; Mars and Neptune have some too. Now Earth is shown to have a Trojan. A search of data collected by NASA's Wide-field Infrared Survey Explorer (WISE) satellite revealed the asteroid 2010 TK7 as a strong candidate, and subsequent optical observations confirm its status as a Trojan companion of Earth, oscillating around the L4 (leading) Lagrange triangular point.

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