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A low density of 0.8 g cm-3 for the Trojan binary asteroid 617 Patroclus

Abstract

The Trojan population consists of two swarms of asteroids following the same orbit as Jupiter and located at the L4 and L5 stable Lagrange points of the Jupiter–Sun system (leading and following Jupiter by 60°). The asteroid 617 Patroclus is the only known binary Trojan1. The orbit of this double system was hitherto unknown. Here we report that the components, separated by 680 km, move around the system's centre of mass, describing a roughly circular orbit. Using this orbital information, combined with thermal measurements to estimate the size of the components, we derive a very low density of . The components of 617 Patroclus are therefore very porous or composed mostly of water ice, suggesting that they could have been formed in the outer part of the Solar System2.

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Figure 1: 617 Patroclus observed with the Keck 10-m telescope on the Mauna Kea summit in Hawaii and its adaptive optics system.
Figure 2: Several good-fit orbits of the 617 Patroclus components estimated using 2004–2005 Keck LGS adaptive optics data.
Figure 3: Relationship between the sample density and the porosity of 617 Patroclus for various compositions.

References

  1. Merline, W. J. et al. S/2001 (617) 1. IAU Circ. 7741 (2001)

  2. Morbidelli, A., Levison, H. F., Tsiganis, K. & Gomes, R. Chaotic capture of Jupiter's Trojan asteroids in the early Solar System. Nature 435, 462–465 (2005)

    Article  ADS  CAS  Google Scholar 

  3. Chapman, C. R. et al. Discovery and physical properties of Dactyl, a satellite of asteroid 243 Ida. Nature 374, 783–785 (1995)

    Article  ADS  CAS  Google Scholar 

  4. Merline, W. J. L., et al. in Asteroids III (eds Bottke, W. F., Cellino, A., Paolicchi, P. & Binzel, R. P.) 289–312 (Univ. Arizona Press, Tucson, 2002)

    Google Scholar 

  5. Pravec, P. et al. Photometric survey of binary near-Earth asteroids. Am. Astron. Soc. Div. Planet. Sci. 36, abstr. 28.04 (2004)

  6. Marchis, F., Descamps, P., Hestroffer, D. & Berthier, J. Discovery of the triple asteroidal system 87 Sylvia. Nature 436, 822–824 (2005)

    Article  ADS  CAS  Google Scholar 

  7. Roth, K. C. et al. Hokupa'a performance and point spread function characterization. Bull. Am. Astron. Soc. 33, abstr. 02.02, 785 (2001)

    ADS  Google Scholar 

  8. Berthier, J. & Marchis, F. A tool for observations of Centaurs/Kuiper Objects with adaptive optics systems. Bull. Am. Astron. Soc. 33, abstr. 12.17, 1049 (2001)

    ADS  Google Scholar 

  9. Marchis, F. et al. in Advancements in Adaptive Optics (eds Bonaccini, D., Ellerbroek, B. L. & Ragazzoni, R.) Proc. SPIE 5490, 338–350 (2004).

  10. Bouchez, A. H. et al. in Advancements in Adaptive Optics (eds Bonaccini, D., Ellerbroek, B. L. & Ragazzoni, R.) Proc. SPIE 5490, 321–330 (2004).

  11. Hestroffer, D. & Vachier, F. Orbit determination of binary asteroids. IAU Symp. 229 on Asteroids, Comets and Meteors (Buzios, Rio de Janeiro, Brazil, 2005) abstr. 10.9, 87 (IAU, 2005)

    Google Scholar 

  12. Descamps, P. Orbit of an astrometric binary system. Celest. Mech. Dynam. Astron. 92, 381–402 (2005)

    Article  ADS  MathSciNet  Google Scholar 

  13. Marchis, F., et al. On the diversity of binary asteroid orbits. IAU Symp. 229 on Asteroids, Comets and Meteors (Buzios, Rio de Janeiro, Brazil, 2005) abstr. 10.1, 83 (IAU, 2005)

    Google Scholar 

  14. Marchis, F. et al. Mass and density of asteroid 121 Hermione from an analysis of its companion orbit. Icarus (in the press)

  15. Veillet, C. et al. The binary Kuiper-belt 1998 WW31. Nature 416, 711–713 (2000)

    Article  ADS  Google Scholar 

  16. Fernandez, Y. et al. The albedo distribution of jovian trojan asteroids. Astron. J. 126, 1563–1574 (2003)

    Article  ADS  Google Scholar 

  17. Emery, J. P., Cruikshank, D. P. & Van Cleve, J. Thermal emission spectroscopy of asteroids with the Spitzer Space Telescope. Am. Astron. Soc. Div. Planet. Sci. 37, abstr. 15.07 (2005)

  18. Merline, W. J. L. et al. Discovery of a moon orbiting the asteroid 45 Eugenia. Nature 401, 565–569 (1999)

    Article  ADS  CAS  Google Scholar 

  19. Marchis, F., Descamps, P., Berthier, J., Hestroffer, D. & de Pater, I. Fine analysis of 121 Hermione, 45 Eugenia, and 90 Antiope binary asteroid systems with AO observations. Am. Astron. Soc. Div. Planet. Sci. 36, abstr. 46.02 (2004)

  20. Descamps, P., et al. Insights on 90 Antiope double asteroid combining VLT-AO and lightcurve observations. IAU Symp. 229 on Asteroids, Comets and Meteors (Buzios, Rio de Janeiro, Brazil, 2005) abstr. 10.7, 87 (IAU, 2005)

    Google Scholar 

  21. Anderson, J. D. et al. Amalthea's density is less than that of water. Science 308 (5726), 1291–1293 (2005)

    Article  ADS  CAS  Google Scholar 

  22. Britt, D. T., Yeomans, D., Housen, K. & Consolmagno, G. in Asteroids III (eds Bottke, W. F., Cellino, A., Paolicchi, P. & Binzel, R. P.) 485–500 (Univ. Arizona Press, Tucson, 2002)

    Google Scholar 

  23. Gladman, B., Quinn, D., Nicholson, P. & Rand, R. Synchronous locking of tidally evolving satellites. Icarus 122, 166–172 (1996)

    Article  ADS  Google Scholar 

  24. Angeli, C. A. et al. A contribution to the study of asteroids with long rotation period. Planet. Space Sci. 47, 699–714 (1999)

    Article  ADS  CAS  Google Scholar 

  25. Michalowski, T. et al. Eclipsing binary asteroid 90 Antiope. Astron. Astrophys. 423, 1159–1168 (2004)

    Article  ADS  Google Scholar 

  26. Tohline, J. E. The origin of binary stars. Annu. Rev. Astron. Astrophys. 40, 349–385 (2002)

    Article  ADS  Google Scholar 

  27. Weidenshilling, S. J., Marzari, F., Davis, D. R. & Neese, C. Origin of the double asteroid 90 Antiope: a continuing puzzle. Lunar Planet. Sci. XXXII, 1890 (2001)

    ADS  Google Scholar 

  28. Goldreich, P., Lithwick, Y. & Re'em, S. Formation of Kuiper-belt binaries by dynamical friction and three-body encounters. Nature 410, 643–646 (2002)

    Article  ADS  Google Scholar 

  29. Astakhov, S. A., Lee, E. A. & Farrelly, D. Formation of Kuiper-belt binaries through multiple chaotic scattering encounters with low-mass intruders. Mon. Not. R. Astron. Soc. 360, 401–415 (2005)

    Article  ADS  Google Scholar 

  30. Walsh, K. J. & Richardson, D. C. Binary near-Earth asteroid formation: rubble pile model of tidal disruptions. Am. Astron. Soc. Div. Planet. Sci. 37, abstr. 14.11 (2005)

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Acknowledgements

This work was supported by the National Science Foundation Science and Technology Center for Adaptive Optics and by the National Aeronautics and Space Administration (NASA) issue through the Science Mission Directorate Research and Analysis programmes. Most of the data were obtained at the W. M. Keck observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California and NASA. Additional observations were obtained at the Gemini Observatory (acquired through the Gemini Science Archive). Author Contributions F.M. and the IMCCE researchers processed, analysed and interpreted the data. The 2004–2005 campaign of observations with Keck LGS adaptive optics was conducted by the team from the W. M. Keck Observatory, and other University of California at Berkeley researchers.

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Correspondence to Franck Marchis.

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Supplementary information

Supplementary Table 1

This Supplementary Table summarizes the measurements performed on each observation for the analysis, such as the relative positions of the components (X, Y based on a fit by a gaussian function in arcsec), the difference of brightness in magnitude, and the residual mean square fitting error of our model. (XLS 18 kb)

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Marchis, F., Hestroffer, D., Descamps, P. et al. A low density of 0.8 g cm-3 for the Trojan binary asteroid 617 Patroclus. Nature 439, 565–567 (2006). https://doi.org/10.1038/nature04350

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