Each giant planet of the Solar System has two main types of moons. ‘Regular’ moons are typically larger satellites with prograde, nearly circular orbits in the equatorial plane of their host planets at distances of several to tens of planetary radii. The ‘irregular’ satellites (which are typically smaller) have larger orbits with significant eccentricities and inclinations. Despite these common features, Neptune's irregular satellite system, hitherto thought to consist of Triton and Nereid, has appeared unusual. Triton is as large as Pluto and is postulated to have been captured from heliocentric orbit; it traces a circular but retrograde orbit at 14 planetary radii from Neptune. Nereid, which exhibits one of the largest satellite eccentricities, is believed to have been scattered from a regular satellite orbit to its present orbit during Triton's capture1,2. Here we report the discovery of five irregular moons of Neptune, two with prograde and three with retrograde orbits. These exceedingly faint (apparent red magnitude mR = 24.2–25.4) moons, with diameters of 30 to 50 km, were presumably captured by Neptune.
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McKinnon, W. B. On the origin of Triton and Pluto. Nature 311, 355–358 (1984)
Goldreich, P., Murray, N., Longaretti, P.-Y. & Banfield, D. Neptune's story. Science 245, 500–504 (1989)
Hogg, D. W. et al. A photographic search for satellites of Neptune. Icarus 107, 304–310 (1994)
Gladman, B. J. et al. Discovery of two distant irregular moons of Uranus. Nature 392, 897–899 (1998)
Brown, M. J. I. & Webster, R. L. A search for distant satellites of Neptune. Publ. Astron. Soc. Austr. 15, 325–327 (1998)
Gladman, B. et al. NOTE: The discovery of Uranus XIX, XX, and XXI. Icarus 147, 320–324 (2000)
Sheppard, S. S. & Jewitt, D. C. An abundant population of small irregular satellites around Jupiter. Nature 423, 261–263 (2003)
Gladman, B. et al. Discovery of 12 satellites of Saturn exhibiting orbital clustering. Nature 412, 163–166 (2001)
Kavelaars, J. J. et al. The discovery of faint irregular satellites of Uranus. Icarus 169, 474–481 (2004)
Hénon, M. Numerical exploration of the restricted problem. VI. Hill's case: non-periodic orbits. Astron. Astrophys. 9, 24–36 (1970)
Nesvorný, D., Alvarellos, J. L. A., Dones, L. & Levison, H. F. Orbital and collisional evolution of the irregular satellites. Astron. J. 126, 398–429 (2003)
Allen, R. L., Bernstein, G. M. & Malhotra, R. The edge of the solar system. Astrophys. J. 549, L241–L244 (2001)
Landolt, A. U. UBVRI photometric standard stars in the magnitude range 11.5–16.0 around the celestial equator. Astron. J. 104, 340–371 (1992)
Gladman, B., Kavelaars, J. J., Nicholson, P. D., Loredo, T. J. & Burns, J. A. Pencil-beam surveys for faint trans-neptunian objects. Astron. J. 116, 2042–2054 (1998)
Alard, C. Image subtraction using a space-varying kernel. Astron. Astrophys. 144(Suppl.), 363–370 (2000)
Petit, J.-M., Holman, M., Scholl, H., Kavelaars, J. & Gladman, B. An automated moving object detection package. Mon. Not. R. Astron. Soc. 347, 471–480 (2004)
Sheppard, S. S. et al. Satellites of Neptune. IAU Circ. No. 8193 (2003)
Heppenheimer, T. A. & Porco, C. New contributions to the problem of capture. Icarus 30, 385–401 (1977)
Ćuk, M. & Burns, J. A. Gas-drag-assisted capture of Himalia's family. Icarus 167 369–381 (2004)
Colombo, G. & Franklin, F. A. On the formation of the outer satellite groups of Jupiter. Icarus 15, 186–189 (1971)
Pollack, J. B., Burns, J. A. & Tauber, M. E. Gas drag in primordial circumplanetary envelopes—A mechanism for satellite capture. Icarus 37, 587–611 (1979)
Astakhov, S. A., Burbanks, A. D., Wiggins, S. & Farrelly, D. Chaos-assisted capture of irregular moons. Nature 423, 264–267 (2003)
Goldreich, P., Lithwick, Y. & Sari, R. Formation of Kuiper-belt binaries by dynamical friction and three-body encounters. Nature 420, 643–646 (2002)
Wisdom, J. & Holman, M. Symplectic maps for the n-body problem. Astron. J. 102, 1528–1538 (1991)
Kozai, Y. Secular perturbations of asteroids with high inclination and eccentricity. Astron. J. 67, 591–598 (1962)
Carruba, V., Burns, J. A., Nicholson, P. D. & Gladman, B. J. On the inclination distribution of the jovian irregular satellites. Icarus 158, 434–449 (2002)
Kessler, D. J. Derivation of the collision probability between orbiting objects: The lifetimes of Jupiter's outer moons. Icarus 48, 39–48 (1981)
Grav, T., Holman, M. J., Gladman, B. J. & Aksnes, K. Photometric survey of the irregular satellites. Icarus 166, 33–45 (2003)
Rettig, T. W., Walsh, K. & Consolmagno, G. Implied evolutionary differences of the jovian irregular satellites from a BVR color survey. Icarus 154, 313–320 (2001)
Grav, T., Holman, M. J. & Fraser, W. Photometry of irregular satellites of Uranus and Neptune. Preprint astro-ph/0405605 at 〈http://www.arXiv.org〉 (2004).
We thank M. Lecar for discussions, and D. Trilling for observing assistance at Magellan. T. Abbott (CTIO) volunteered to observe during Director's Discretionary time. CTIO is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under a cooperative agreement with the National Science Foundation as part of the National Optical Astronomy Observatories. The CFHT is operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii. The VLT is operated by the European Southern Observatory. This work was supported by NASA and the Smithsonian Institution.
The authors declare that they have no competing financial interests.
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Holman, M., Kavelaars, J., Grav, T. et al. Discovery of five irregular moons of Neptune. Nature 430, 865–867 (2004). https://doi.org/10.1038/nature02832
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