Ring System Around Pluto?

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With the New Horizons spacecraft on its way to Pluto, there may be an intriguing additional task for the mission’s science team: look for a potential ring around Pluto and its moons. Researchers at The Universidade Estadual Paulista in Brazil have recently submitted a paper for publication in which they explore the possibility of a ring system around the Pluto-Charon system.  In their paper, the team discusses the effects of micrometeoroid impacts on Nix and Hydra and how the resulting dust particles could form a ring around Pluto.  The team also investigates forces, such as the solar wind, which would dissipate said ring system.


Pryscilla Maria Pires dos Santos and her team provide an exhaustive list of calculations in their paper which estimates the ring system to have a diameter of nearly 16,000 kilometers – well outside the orbits of Nix and Hydra.  Based on their calculations, Pires dos Santos state that despite nearly 50% of the ring’s mass being dissipated within a year, a tenuous ring system can be maintained by the dust expelled by micrometeoroid impacts.

Additional data presented in the paper places the rings “optical depth” as being several orders of magnitude fainter than even Jupiter’s rings. (Yes, Jupiter has a ring system!)  While ground-based observatories and even the Hubble Space Telescope haven’t detected the ring system Pires dos Santos et al. are hopeful that the New Horizons mission will provide data to validate their theoretical models. New Horizons has a dust counter capable of measuring dust grains with a minimum mass of 10-12 grams, which should provide the data required to support or refute the team’s models.

Pires dos Santos mentions: “It is worth to point out that the interplanetary environment in the outer Solar System is not well known. Many assumptions have to be made in order to estimate a normal optical depth of a putative ring encompassing the orbits of Nix and Hydra.

If you’d like to read the full paper, you can access it  (for free) at: http://arxiv.org/PS_cache/arxiv/pdf/1108/1108.0712v1.pdf

Source: arXiv:1108.0712v1 [astro-ph.EP]

Double Occultations This Week Will Reveal More Details About Pluto

Several teams of astronomers are taking advantage of a rare double event this week to learn more about the atmosphere and makeup of Pluto and its moons. The dwarf planet will occult, or pass in front of two different stars this week. One of the best viewing sites for these two events is in Hawaii, and eclipse-chaser Dr. Jay Pasachoff is there to record both events. “To see those occultations, we have to be in a particular set of places on Earth, those over which the shadow of the object in starlight passes,” Pasachoff wrote in a guest post on the Planet Hunters blog. “Since the stars are so far away, their light is essentially parallel and the shadows of the objects on Earth are the same as the sizes of the objects.”

If all goes well, we will know a lot more about the Pluto system, Pasachoff said.

Map of where the occultation would be visible on June 22-23, 2011.

Last night, June 22/23, both Pluto and its moon Charon occulted a magnitude 14.4 star, with each occultation lasting a minute or so and separated from each other by 12 minutes. “The event is particularly exciting because if we capture both Pluto and Charon nearly simultaneously, we can find out about the system’s internal orbits with higher precision than before, perhaps allowing a refinement of the center of mass and thus the masses and densities of each object,” Pasachoff said.

Also, the first deployment for an occultation of the NASA/German SOFIA observatory took place last night to view the Pluto occultation, flying at an altitude of 43,000 feet off the west coast of Central America.

“The scientific goal is to catch the ‘central flash,’ which conveys vital information about conditions in Pluto’s global atmosphere,” wrote American Astronomical Society press officer Rick Fienberg on Twitter. Fienberg was part of the press corps that was accompanying the flight.

On Sunday/Monday night, June 26/27, Pluto will occult a different star, and over a much narrower path, its small moon Hydra might also occult another star.

Pasachoff said that the most recent predictions for last night’s occulations shifted the prediction south, so that Hawaii is slightly off the main predicted path, to its north. But other teams are in Cairns, Australia, to see if it goes that far south.

For the June 26/27 event (June 27 UT but June 26 in Hawaii), the star is magnitude 13.6. “That is a couple of magnitudes brighter than most of the stars we have observed being occulted,” Pasachoff said, “so the data would be particularly low-noise. In addition to the occultation of Pluto itself, whose southern limit is predicted to pass through the Hawaiian islands, the tiny Pluto moon Hydra is to be occulted, though that narrow path’s prediction now passes north of the Hawaiian islands. We have arranged for telescopes in Yunnan, China, in Japan, Taiwan, and Thailand to observe with us, and MIT’s Matt Lockhart is en route to Yunnan with one of our POETS (Portable Occultation, Eclipse, and Transit System) cameras. We have Australian sites still observing as well, just in case the actual path is hundreds of kilometers south of the predictions.”

Earlier occultations by Pluto studied by Pasachoff and his colleagues showed that Pluto’s atmosphere was warming and that the atmosphere would probably remain warm enough by 2015 for the New Horizons spacecraft to detect and study it with its on-board instruments, and was part of the incentive for the mission to launch when it did.

To learn more about the occultations and the research, check out this main stellar occultation website from Williams College, where Pasachoff is located, which has links to the work of other researchers as well.

Maps and details of the predictions can be found here, and more details about Pluto occultations websites can be found here.

We’ll try to provide an update of the events when details become available.

You can follow Universe Today senior editor Nancy Atkinson on Twitter: @Nancy_A. Follow Universe Today for the latest space and astronomy news on Twitter @universetoday and on Facebook.

Pluto’s Moons, Nix and Hydra, may have been Adopted

 

How many moons does Pluto have? The mini-moons of Pluto, Nix and Hydra, were discovered in 2005 (but named in 2006) during an observation campaign by the Hubble Space Telescope. The discovery of these mini-moons increase the number of natural satellites orbiting Pluto to three (including larger moon Charon). But where did these satellites come from? The current accepted theory on the formation on the large moon, Charon, is much like the theory supporting the creation of Earth’s Moon. It is thought that a large impact between two Large Kuiper Belt Objects chipped Charon away from a proto-Pluto, putting the chunk of Pluto mass into orbit. Over the years, tidal forces slowed the pair and Charon was allowed to settle into its present-day orbit. Recent theory suggests that Nix and Hydra are a by product of this collision, merely shattered fragments of the huge impact. But there are problems with this idea. Could Nix and Hydra have come from somewhere other than the Pluto-Charon impact?

The orbits of Plutos moons, Charon, Nix and Hydra (credit: NASA)
The small moons that orbit the Large Kuiper Belt Object (formerly classified as a planet) can be found about 48,700 kilometers and 64,800 kilometers from the surface of Pluto. The closest moon is called Nix and the farthest, Hydra. Nix has an orbital resonance of 4:1 with Charons orbit and the larger moon Hydra has a resonance of 6:1 (i.e. Nix will orbit Pluto once for every four of Charons orbits; Hydra will orbit Pluto once for every six of Charons orbits).

The reasons behind these mini-moon orbits are only just beginning to be understood, but it is known that their resonances with Charons orbit is rooted way back during the Pluto-system evolution. If we assume Hydra and Nix were formed from a massive Kuiper Belt Object collision, the easiest explanation is to assume they are whole fragments from the impact caught in the gravity of the Pluto-Charon system. However, due to the highly eccentric orbits that would have resulted from this collision, it is not possible that the two little moons could have evolved into a near-circular orbit, in near-corotational resonance with Charon.

So, could it be possible that the moons may have formed from the dust and debris resulting from the initial collision? If there was enough material produced, and if the material collided frequently, then perhaps Nix and Hydra were born from a cold disk of debris (rather than being whole pieces of rock), eventually coalescing and forming sizeable rocky moons. As there may have been a disk of debris, collisions with the orbiting Nix and Hydra would have also reduced any eccentricity in their orbits.

But there is a big problem with this theory. From impact simulations, the post-impact disk of debris surrounding Pluto would have been very compact. The disk could not have reached as far as the present-day orbits of the moons.

One more theory suggests that perhaps the moons were created in a post-impact disk, but very close to Pluto, and then through gravitational interactions with Charon, the orbits of Nix and Hydra were pulled outward, allowing them to orbit far from the Pluto-Charon post-impact disk. According to recent computer simulations, this doesn’t seem to be possible either.

To find an answer, work by Yoram Lithwick and Yanqin Wu (University of Toronto) suggest we must look beyond the Pluto-Charon system for a source of material for Nix and Hydra. From simulations, the above theories on the creation of the small moons being started by material ejected from a large collision between two Large Kuiper Belt Objects (creating Pluto and Charon) are extremely problematic. They do not correctly answer how the highly eccentric orbits Nix and Hydra would have from a collision could evolve into the near-circular ones they have today.

Lithwick and Wu go on to say that the circular, corotational resonant orbits of the two moons could be created from a Plutocentric disk of small bits of rock scooped up during Pluto’s orbit around the Sun. Therefore Nix and Hydra may have been formed from the rocky debris left over from the development of the Solar System, and not from a collision event creating Charon. This may hold true for the countless other Kuiper Belt Objects in orbit in the far reaches of the Solar System, no impact is necessary for the creation of the tiny moons now thought to be their satellites.

It is hoped that the New Horizons mission (launched January 21st, 2006) to the far reaches of the Solar System will reveal some of the questions that remain unanswered in the depths of our mysterious Kuiper Belt. Hopefully we will also find out whether Nix and Hydra are children of Pluto and Charon… or whether they were adopted.

Source: arXiv