The discovery of two new satellites of Pluto
Abstract
The planet Pluto was discovered in 1930, and is roughly 70% the size of the Earth's moon. Its satellite Charon, about half the size of Pluto, was discovered in 1978. On October 31, 2005, we announced the discovery of two additional satellites of Pluto (IAU Circular 8625), provisionally designated S/2005 P 1 and S/2005 P 2. These new satellites were identified in Hubble Space Telescope observations made between May 15-18, 2005, with the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC). We also found evidence that these satellites were marginally detected in earlier ACS High Resolution Channel (HRC) images obtained in 2002, near the locations predicted by our best orbital solutions, which provides some independent support for this discovery.
P 1 and P 2 have visual magnitudes V = 22.93 +/- 0.12 and V = 23.38 +/- 0.17, respectively, which implies diameters roughly 3-14% that of Charon, or 100 km +/- 60 km, depending on their albedos. Definitive orbits cannot be calculated from the available data, but their measured positions are consistent with objects located in Charon's orbital plane with little or no eccentricity. We estimate that P 1 and P 2 are orbiting at barycentric radii of 64,700 km and 49,400 km, respectively -- or 3.7 and 2.8 times the orbital radius of Charon. We calculate orbital periods of 38.2 and 25.5 days for P 1 and P 2, respectively, which suggest possible 6:1 and 4:1 mean motion orbital resonances with Charon (period 6.4 days). Since our data shows no evidence for satellites beyond P 1, to a limiting magnitude of V = 26.2 (90% confidence), this makes for a surprisingly compact ``quadruple planet" system, which occupies only the inner 3% of Pluto's orbital stability zone. We will describe the discovery observations, and our ongoing efforts to characterize these new satellites (with further Hubble and ground-based observations) at this pivotal moment: with the New Horizons mission set to launch during the AAS Meeting, on January 11, 2006. Further information is available on our team webpage: http://www.boulder.swri.edu/plutonews/- Publication:
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American Astronomical Society Meeting Abstracts #207
- Pub Date:
- June 2006
- Bibcode:
- 2006AAS...207.0423M