More Moons Around Pluto? Options

[JRehling]

Press Release Source: NASA


NASA's Hubble Reveals Possible New Moons Around Pluto
Monday October 31, 12:30 pm ET


WASHINGTON, Oct. 31 /PRNewswire/ -- Using NASA's Hubble Space Telescope to view the ninth planet in our solar system, astronomers discovered Pluto may have not one, but three moons.
If confirmed, the discovery of the two new moons could offer insights into the nature and evolution of the Pluto system; Kuiper Belt Objects with satellite systems; and the early Kuiper Belt. The Kuiper Belt is a vast region of icy, rocky bodies beyond Neptune's orbit.

"If, as our new Hubble images indicate, Pluto has not one, but two or three moons, it will become the first body in the Kuiper Belt known to have more than one satellite," said Hal Weaver of the Johns Hopkins Applied Physics Laboratory, Laurel, Md. He is co-leader of the team that made the discovery.

Pluto was discovered in 1930. Charon, Pluto's only confirmed moon, was discovered by ground-based observers in 1978. The planet resides about 3 billion miles from the sun in the heart of the Kuiper Belt.

"Our result suggests other bodies in the Kuiper Belt may have more than one moon. It also means planetary scientists will have to take these new moons into account when modeling the formation of the Pluto system," said Alan Stern of the Southwest Research Institute, Boulder, Colo. Stern was co-leader of the research team.

The candidate moons, provisionally designated S/2005 P1 and S/2005 P2, were observed approximately 27,000 miles away from Pluto. The objects are roughly two to three times as far from Pluto as Charon.

The team plans to make follow-up Hubble observations in February to confirm the newly discovered objects are truly Pluto's moons. Only after confirmation will the International Astronomical Union consider names for S/2005 P1 and S/2005 P2.

The Hubble's Advanced Camera for Surveys observed the two new candidate moons on May 15, 2005. The candidates are roughly 5,000 times fainter than Pluto. Three days later, Hubble looked at Pluto again. The two objects were still there and appeared to be moving in orbit around Pluto.

The team looked long and hard for other potential moons around Pluto. "These Hubble images represent the most sensitive search yet for objects around Pluto," said team member Andrew Steffl of the Southwest Research Institute. "It is unlikely that there are any other moons larger than about 10 miles across in the Pluto system," he said.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. The Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington.


For detailed information and images about this research on the Web, visit:

http://hubblesite.org/news/2005/19

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home




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Source: NASA

[ljk4-1]

Paper: astro-ph/0511837

Date: Wed, 30 Nov 2005 19:37:52 GMT (124kb)

Title: New Constraints on Additional Satellites of the Pluto System

Authors: A.J. Steffl, M.J. Mutchler, H.A. Weaver, S.A.Stern, D.D. Durda, D.
Terrell, W.J. Merline, L.A. Young, E.F. Young, M.W. Buie, and J.R. Spencer

Comments: 18 pages including 4 figures
\\
Observations of Pluto and its solar-tidal stability zone were made using the
Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) on UT
2005 May 15 and UT 2005 May 18. Two small satellites of Pluto, provisionally
designated S/2005 P 1 and S/2005 P 2, were discovered and are reported by
(Weaver et al. 2005). These observations also provide strong constraints on the
existence of any additional satellites of Pluto. We place a 90%-confidence
lower limit of V=26.2 (V=27.1 for a 50%-confidence lower limit) on the
magnitude of undiscovered satellites >5" from Pluto. Assuming an albedo of
p_v=0.04 (similar to cometary nucleii and a reasonable lower limit), this
corresponds to a limiting diameter of 37 km at 90%-confidence (25 km at
50-confidence). For an assumed albedo similar to Charon, i.e p_v=0.38, the
magnitude limit corresponds to a limiting diameter of 12 km at 90%-confidence
(8 km at 50%-confidence). At distances <5" from Pluto, scattered light from
both Pluto and Charon degrades the sensitivity of our search, such that at 1.7"
from Pluto the 50%-confidence magnitude limit is V=25.3, corresponding to a
limiting diameter of 57 km for an object with p_v=0.04.

\\ ( http://arXiv.org/abs/astro-ph/0511837 , 124kb)

[Rob Pinnegar]

It's good to see that some abstracts are starting to come out of the two new Plutonian moons.

Not to harp on this too much, but I'm still *really* interested to see how much Charon perturbs their orbits. A few weeks back (in this thread) I tried to figure out a rough estimate of this effect, but my attempt was ridiculously oversimplified as it didn't take into account the rotating frame of reference (as seen from 2005 P1 and P2). It'll be neat to see the real solution.

[Comga]

Not to harp on this too much, but I'm still *really* interested to see how much Charon perturbs their orbits.

The article in the link and the original one both indicate that the new moons are in resonant orbits with Pluto-Charon and their 6.3 day rotation. They may be in the fourth and sixth harmonic orbits. (I don't have the original article to repeat the calculation.) Whether you can say that Charon "perturbs" the orbit or "regulates" them is semantics, but the system isn't chaotic. As for your simple model, determining how large the libration swings can be would require some real sophistication.