S/2011 P 1

S/2011 P 1

Hubble Space Telescope discovery images of S/2011 P 1.
Discovery[1]
Discovered by	Showalter, M. R. et al.
Discovery date	June 28, 2011 (verified July 20, 2011)
Orbital characteristics[1]
Mean orbit radius	(59 ± 2)×103 km
Eccentricity	≈ 0
Orbital period	32.1 ± 0.3 days
Inclination	≈ 0
Satellite of	Pluto
Physical characteristics
Apparent magnitude	26.1 ± 0.3[1]

Orbits of the four moons of Pluto

S/2011 P 1 (also known as S/2011 (134340) 1^{[note 1]} or P4) is a small natural satellite of Pluto whose existence was announced on July 20, 2011.^[1] Its discovery, following the discoveries of Charon in 1978 and Nix and Hydra in 2005, made it Pluto's fourth known moon.

Discovery

S/2011 P 1 was discovered by the Hubble Space Telescope's Pluto Companion Search Team on June 28, 2011, using the Wide Field Camera 3, during an attempt to find any rings that Pluto might possess.^{[note 2][4]} Further observations were made on July 3 and July 18, 2011 and it was verified as a new moon on July 20, 2011.^[1][5] It was later identified in archival Hubble images from February 15, 2006 and June 25, 2010.^[1] S/2011 P 1's brightness is only about 10% of that of Nix, and it was found because the discovery team took 8-minute exposures; earlier observations had used shorter exposures.^[6]

Physical properties

With an estimated diameter of 13–34 km (8–21 mi), S/2011 P 1 is the smallest known moon of Pluto.^[7][8] This diameter range is derived from an assumed possible geometric albedo range of 0.06 to 0.35.^[1][6]

Orbital properties

Current observations suggest a circular, equatorial orbit with a radius of approximately 59,000 km (about 37,000 miles).^[1][6] The moon orbits in the region between Nix and Hydra and makes a complete orbit of Pluto roughly every 32.1 Earth days.^[1][6] This period is close to a 1:5 orbital resonance with Charon, with the timing discrepancy being apparently less than 0.6%. As with the near resonances between Nix or Hydra and Charon (1:4 and 1:6, respectively), determining how close this relationship is to a true resonance will require more accurate knowledge of S/2011 P 1's orbit, in particular its rate of precession.

Origin

Like Pluto's other satellites,^[9] it is suspected that S/2011 P 1 coalesced from the debris of a massive collision between Pluto and another Kuiper belt object, similar to the "big whack" believed to have created the Earth's Moon.^[4]

Naming

A formal name for S/2011 P 1 will probably be proposed to the International Astronomical Union by the discovery team. According to team leader Mark Showalter, a name associated with Hades and the underworld will be chosen from Greek mythology.^[10]

See also

• Moons of Pluto

Notes

1. ^ 134340 is Pluto's Minor Planet Center number, assigned following its demotion from full planetary status in 2006. S/2011 P 1 is the format used for planetary satellites.
2. ^ The search for rings is motivated in part by a desire to avoid damage to the New Horizons spacecraft when it passes through the Pluto system in July 2015.^[2][3]

References

1. ^ ^{a b c d e f g h i} Showalter, M. R.; Hamilton, D. P. (2011-07-20). "New Satellite of (134340) Pluto: S/2011 (134340) 1". Central Bureau for Astronomical Telegrams. International Astronomical Union. http://www.cbat.eps.harvard.edu/cbet/cbet002769.txt. Retrieved 2011-07-20. 
2. ^ Wall, M. (2011-07-20). "New Pluto Moon Foreshadows More Surprises for NASA Probe En Route". Space.Com web site. TechMediaNetwork. http://www.space.com/12372-pluto-fourth-moon-nasa-spacecraft.html. Retrieved 2011-07-21. 
3. ^ McKee, M. (2006-02-22). "Rings of ice and dust may encircle Pluto". New Scientist web site. New Scientist. http://www.newscientist.com/article/dn8760-rings-of-ice-and-dust-may-encircle-pluto.html. Retrieved 2011-07-21. 
4. ^ ^{a b} Boyle, A. (2011-07-20). "Scientists spot Pluto's fourth moon". Cosmic Log on msnbc.com. msnbc.com. http://cosmiclog.msnbc.msn.com/_news/2011/07/20/7119984-scientists-spot-plutos-fourth-moon. Retrieved 2011-07-20. 
5. ^ Pluto Has Another Moon, Hubble Photos Reveal | Dwarf Planet Pluto | Pluto's Moons | Space.com
6. ^ ^{a b c d} Lakdawalla, E. (2011-07-20). "A fourth moon for Pluto". Planetary Society weblog. The Planetary Society. http://www.planetary.org/blog/article/00003107/. Retrieved 2011-07-20. 
7. ^ "NASA's Hubble Discovers Another Moon Around Pluto". http://www.nasa.gov/mission_pages/hubble/science/pluto-moon.html. Retrieved 2011-07-20. 
8. ^ "Tiny fourth moon discovered in Pluto's orbit". CNN. http://www.cnn.com/2011/US/07/20/us.pluto.moon/. Retrieved 2011-07-20. 
9. ^ Stern, S. A.; Weaver, H. A.; Steff, A. J.; Mutchler, M. J.; Merline, W. J.; Buie, M. W.; Young, E. F.; Young, L. A.; Spencer, J. R. (2006-02-23). "A giant impact origin for Pluto’s small moons and satellite multiplicity in the Kuiper belt". Nature 439 (7079): 946–948. Bibcode 2006Natur.439..946S. doi:10.1038/nature04548. PMID 16495992. http://ns1.plutoportal.net/~layoung/eprint/Stern2006plutosat.pdf. Retrieved 2011-07-20. 
10. ^ Shiga, D. (2011-07-20). "What should Pluto's new moon be named?". New Scientist web site. New Scientist. http://www.newscientist.com/blogs/shortsharpscience/2011/07/what-should-plutos-new-moon-be.html. Retrieved 2011-07-21.