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TOPIC: Pluto
Blobrana


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RE: Pluto
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Title: On the Origin of Pluto's Minor Moons, Nix and Hydra
Authors: Yoram Lithwick, Yanqin Wu

How did Pluto's recently discovered minor moons form? Ward and Canup propose an elegant solution in which Nix and Hydra formed in the collision that produced Charon, then were caught into corotation resonances with Charon, and finally were transported to their current location as Charon migrated outwards. We show with numerical integrations that, if Charon's eccentricity is judiciously chosen, this scenario works beautifully for either Nix or Hydra. However, it cannot work for both Nix and Hydra simultaneously. To transport Nix, Charon's eccentricity must satisfy e_C< 0.024; otherwise, the second order Lindblad resonance at 4:1 overlaps with the corotation resonance, leading to chaos. To transport Hydra, e_C > 0.7 R_p/a_C > 0.04; otherwise migration would be faster than libration, and Hydra would slip out of resonance. These two restrictions conflict. Having ruled out this scenario, we suggest an alternative: that many small bodies were captured from the nebular disk, and they were responsible for forming, migrating and damping Nix and Hydra. If this is true, small moons could be common around large Kuiper belt objects.

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Blobrana


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Title: The Effect of Charon's Tidal Damping on the Orbits of Pluto's Three Moons
Authors: Yoram Lithwick, Yanqin Wu

Pluto's recently discovered minor moons, Nix and Hydra, have almost circular orbits, and are nearly coplanar with Charon, Pluto's major moon. This is surprising because tidal interactions with Pluto are too weak to damp their eccentricities. We consider an alternative possibility: that Nix and Hydra circularise their orbits by exciting Charon's eccentricity via secular interactions, and Charon in turn damps its own eccentricity by tidal interaction with Pluto. The timescale for this process can be less than the age of the Solar System, for plausible tidal parameters and moon masses. However, as we show numerically and analytically, the effects of the 2:1 and 3:1 resonant forcing terms between Nix and Charon complicate this picture. In the presence of Charon's tidal damping, the 2:1 term forces Nix to migrate outward and the 3:1 term changes the eccentricity damping rate, sometimes leading to eccentricity growth. We conclude that this mechanism probably does not explain Nix and Hydra's current orbits. Instead, we suggest that they were formed in-situ with low eccentricities.
We also show that an upper limit on Nix's migration speed sets a lower limit on Pluto-Charon's tidal circularisation timescale of >10^5 yrs. Moreover, Hydra's observed proper eccentricity may be explained by the 3:2 forcing by Nix.

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Blobrana


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OccultationPrediction - Pluto and Charon



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Blobrana


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Title: Masses of Nix and Hydra
Authors: David J. Tholen, Marc W. Buie, William M. Grundy, Garrett T. Elliott

A four-body orbit solution for the Pluto system yields GM values of 870.3 ± 3.7, 101.4 ± 2.8, 0.039 ± 0.034, and 0.021 ± 0.042 km³ sec-2 for Pluto, Charon, Nix, and Hydra, respectively. Assuming a Charon-like density of 1.63 gm cm-3, the implied diameters for Nix and Hydra are 88 and 72 km, leading to visual geometric albedos of 0.08 and 0.18, respectively, though with considerable uncertainty. The eccentricity of Charon's orbit has a significant nonzero value; however, the 0.030 ± 0.009 deg yr-1 rate at which the line of apsides precesses is insufficient to explain the difference in the longitude of periapsis seen in the orbits fitted to the 1992-1993 and 2002-2003 data sets. The mean orbital periods for Hydra, Nix, and Charon are in the ratios of 6.064 ± 0.006 : 3.991 ± 0.007 : 1, but we have not identified any resonant arguments that would indicate the existence of a mean motion resonance between any pairs of satellites.

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Blobrana


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Almost 30 years after the discovery of Pluto's large moon, Charon, a University of Hawaii astronomer has used a ground-based telescope to take an image of the Pluto system that exceeds the sharpness possible with the Hubble Space Telescope.

Nix and Hydra

Nix and Hydra

Pluto and Charon
Pluto and Charon

Charon's motion
Charon's motion

Pluto system
The Pluto System

Source

-- Edited by Blobrana at 23:08, 2007-10-12

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Blobrana


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New images of Pluto and its moons are among the sharpest ever made, astronomers announced Friday.
Pluto, long called a planet, was downgraded last year to "dwarf planet" status by the International Astronomical Union. It is so far away that no clear pictures of it exist.

PLU_ge4
Expand (56kb, 560 x 400)
Credit: David Tholen / IfA / Univ. of Hawaii

An image of the Pluto system taken with the one of the ground-based Keck telescopes in Hawaii. The Pluto system moved with respect to the background stars during the one hour of observations, leaving the stars trailed in this image.
The large white dot near the centre of this image is Pluto, with a smaller dot representing its largest moon, Charon. The two specks in the upper right are Nix and Hydra, Pluto's recently discovered mini-moons.

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Blobrana


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(134340) Pluto
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Pluto and its large moon Charon may have been bowled over when they were struck by wayward space rocks in the past, a new study suggests. If so, NASA's New Horizons spacecraft may find evidence of these rolls when it arrives at the distant worlds in 2015.
Jay Melosh of the University of Arizona in Tucson, US, first suggested about 30 years ago that the basins gouged out by impacts would redistribute the mass of planetary bodies, causing them to roll over to re-stabilise themselves.
This mechanism may have caused Earth's Moon which boasts the biggest impact crater in the solar system to roll over so that the crater moved from the equator to the south pole. Similarly, a low-mass region of geysers on Saturn's moon Enceladus may have caused that icy world to rotate, as well.
Now, Francis Nimmo of the University of California in Santa Cruz, US, who led the Moon and Enceladus studies, says impacts may also have caused Pluto and Charon to flip over on their sides.

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Blobrana


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Cryovolcanism
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 Dr. Ted Roush, a scientist at Ames, co-authored a paper titled "Near-Infrared Spectroscopy of Charon: Possible Evidence for Cryovolcanism on Kuiper Belt Objects" in the Astrophysical Journal.
Charon is a Kuiper Belt object that is either the largest moon of Pluto or one member of a double dwarf planet along with Pluto.
The paper included information on crystalline water ice at the surface that was likely due to the presence of ammonia hydrate. Ammonia hydrate lowers the melting point of crystalline water ice and the resulting liquid can be emplaced on the surface by volcanic activity.

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Blobrana


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Pluto
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As a planet, Pluto was a real dog. Now scientists say there may be something truly fishy about one the little world's three known moons.
Astronomers have announced they have evidence that, despite the bitterly cold conditions on the edge of the solar system, Pluto's moon Charon may have an underground ocean of liquid water, triggering speculation it could harbour marine life.
The water appears to be spewing up through cracks in the surface, producing spectacular geysers that instantly freeze, creating showers of ice.

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Blobrana


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Charon
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Frigid geysers spewing material up through cracks in the crust of Plutos companion Charon and recoating parts of its surface in ice crystals could be making this distant world into the equivalent of an outer solar system ice machine.
Evidence for these ice deposits comes from high-resolution spectra obtained using the Gemini Observatorys Adaptive Optics system, ALTAIR coupled with the near-infrared instrument NIRI. The observations, made with the Frederick C. Gillett Gemini North telescope on Hawaiis Mauna Kea, show the fingerprints of ammonia hydrates and water crystals spread in patches across Charon, and have been described as the best evidence yet for the existence of these compounds on worlds such as Charon. The observations suggest that liquid water mixed with ammonia from deep within Charon is pushing out to the ultra-cold surface. This action could be occurring on timescales as short as a few hours or days, and at levels that would recoat Charon to a depth of one millimetre every 100,000 years. This discovery could have profound implications for other similar-type worlds in the Kuiper Belt, which is the region of the solar system that extends out beyond the orbit of Neptune and contains a number of small bodies, the largest of which include Pluto and Charon.

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