Pluto's first known satellite, Charon, was discovered1 in 1978. It has a diameter (∼1,200 km) about half that of Pluto2,3,4,17, which makes it larger, relative to its primary, than any other moon in the Solar System. Previous searches for other satellites around Pluto have been unsuccessful5,6,7, but they were not sensitive to objects ≲150 km in diameter and there are no fundamental reasons why Pluto should not have more satellites6. Here we report the discovery of two additional moons around Pluto, provisionally designated S/2005 P 1 (hereafter P1) and S/2005 P 2 (hereafter P2), which makes Pluto the first Kuiper belt object known to have multiple satellites. These new satellites are much smaller than Charon, with estimates of P1's diameter ranging from 60 km to 165 km, depending on the surface reflectivity; P2 is about 20 per cent smaller than P1. Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon, with orbital periods of ∼38 days (P1) and ∼25 days (P2).
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Christy, J. W. & Harrington, R. S. The satellite of Pluto. Astron. J. 83, 1005–1008 (1978)
Buie, M. W., Tholen, D. J. & Horne, K. Albedo maps of Pluto and Charon—Initial mutual event results. Icarus 97, 211–227 (1992)
Young, L. A. Bulk Properties and Atmospheric Structure of Pluto and Charon. PhD thesis, MIT (1994)
Sicardy, B. et al. Charon's size and an upper limit on its atmosphere from a stellar occultation. Nature 439, 52–54 (2006)
Stern, S. A., Parker, J. W., Fesen, R. A., Barker, E. S. & Trafton, L. M. A search for distant satellites of Pluto. Icarus 94, 246–249 (1991)
Stern, S. A., Parker, J. W., Duncan, M. J., Snowdall, J. C. J. & Levison, H. F. Dynamical and observational constraints on satellites in the inner Pluto-Charon system. Icarus 108, 234–242 (1994)
Stern, S. A. Does the Pluto system contain additional satellites? Lunar Planet. Inst. Conf. XXXIV, abst. 1106 (2003)
Hartig, G. F., Krist, J. E., Martel, A. R., Ford, H. C., Illingworth, G. D. . Proc. SPIE 4854, 532–543 (2003)
Bernstein, G. M. et al. The size distribution of trans-Neptunian bodies. Astron. J. 128, 1364–1390 (2004)
Russell, H. N. On the albedo of the planets and their satellites. Astrophys. J. 43, 173–195 (1916)
Lamy, P. L., Toth, I., Fernandez, Y. R. & Weaver, H. A. in Comets II (eds Festou, M. C., Keller, H. U. & Weaver, H. A.) 223–264 (Univ. Arizona Press, Tucson, 2004)
Marcialis, R. L. et al. The albedos of Pluto and Charon—Wavelength dependence. Astron. J. 103, 1389–1394 (1992)
Steffl, A. J. et al. New constraints on additional satellites of the Pluto system. Astron. J. (submitted); preprint at http://arXiv.org/astrophys/0511837
Stern, S. A. et al. A giant impact origin for Pluto's small moons and satellite multiplicity in the Kuiper belt. Nature doi:10.1038/nature04548 (this issue)
Sirianni, M. et al. The photometric performance and calibration of the Hubble Space Telescope Advanced Camera for Surveys. Publ. Astron. Soc. Pacif. 117, 1049–1112 (2005)
Allen, C. W. Astrophysical Quantities 3rd edn (Atholone, London, 1976)
Gulbis, A. A. S. et al. Charon's radius and atmospheric constraints from observations of a stellar occultation. Nature 439, 48–51 (2006)
We thank G. Hartig for discussions of the ACS optical performance and for examining the images discussed here. We thank the Directors and staff at the Keck, Very Large Telescope, and Gemini observatories for their efforts in attempting ground-based recoveries of these new satellites under non-optimal conditions. We thank the Director and staff of the Space Telescope Science Institute (STScI) for their support of the Hubble Space Telescope observations. Support for this work was provided by NASA through a grant from the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
About this article
Cite this article
Weaver, H., Stern, S., Mutchler, M. et al. Discovery of two new satellites of Pluto. Nature 439, 943–945 (2006). https://doi.org/10.1038/nature04547
Space Science Reviews (2019)
Space Science Reviews (2018)
Nature Astronomy (2017)