Abstract
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).
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Rent or buy this article
Prices vary by article type
from$1.95
to$39.95
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
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)
Acknowledgements
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.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Competing interests
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
Supplementary information
Background Information
Pluto, the most distant planet in our Solar System, has been known for nearly 30 years to have a moon - Charon - about half as wide as the planet itself. Although some scientists suspected that the planet may have other, smaller moons, at such a great distance from the Earth they would be very hard to spot.
Now two such moons have been seen for the first time. Hal Weaver and co-workers report in Nature that they have found them in images taken by the Hubble Space Telescope. Compared with Charon, the two new moons, called P1 and P2, are tiny. Their exact size is hard to gauge, but reasonable assumptions about their reflectivity indicate that they are both between 48 and 165 kilometres across, compared with Charon's diameter of about 1,200 kilometres. The researchers estimate that P1 orbits Pluto once every 38 days, and P2 every 25 days.
Where did these moons come from? Charon is believed to have formed, like our own Moon, from the debris created when another object slammed into its parent planet. In a second, related paper, Alan Stern and colleagues suggest that a small amount of the material from this impact on Pluto gathered together under its own gravity to form P1 and P2.
The Flash Plugin
You will need the Flash browser plugin to view this video. Download the Flash Plugin here: http://www.macromedia.com/go/getflashplayer
Rights and permissions
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
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1038/nature04547
This article is cited by
-
Orbit determination of the moons of the Pluto–Charon system
Celestial Mechanics and Dynamical Astronomy (2022)
-
Circumplanetary Dust Populations
Space Science Reviews (2019)
-
Dust Phenomena Relating to Airless Bodies
Space Science Reviews (2018)
-
The Pluto system after the New Horizons flyby
Nature Astronomy (2017)
-
Resonant interactions and chaotic rotation of Pluto’s small moons
Nature (2015)
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.