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TOPIC: Pluto


L

Posts: 131433
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Hydra and Nix
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The names Nix and Hydra have been approved for the two small satellites of Pluto discovered in May 2005. The International Astronomical Union (IAU), the internationally recognized authority for assigning designations to celestial bodies, approved the names this week.



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RE: Pluto
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Pluto II Nix = S/2005 P 2
Pluto III Hydra = S/2005 P 1

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Nix and Hydra
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Pluto's twin moons, formerly known as S/2005 P 1 and S/2005 P 2, have been christened Nix and Hydra. The objects, discovered last year by the Hubble Space Telescope, received their names from the International Astronomical Union (IAU). A formal announcement will be issued this Friday, 23 June.

The names were proposed this spring by the discovery team, who first identified the moons in May of last year.
In mythology, Pluto ruled the underworld. Nyx was the goddess of night and the mother of Charon, the boatman who takes souls across the River Styx. Pluto's large satellite, discovered in 1978, is called Charon. Because an asteroid with the name Nyx already exists, the IAU decided to use a slightly different spelling for the inner one of the two small Plutonian moons, to avoid confusion. Hydra was the mythological nine-headed serpent that guarded the underworld. A large but inconspicuous constellation in the spring sky also bears this name.

Pluto-philes read even more significance into the two names. The first letters, N and H, also refer to NASA's New Horizons spacecraft, which was launched in January and is now on its way to an encounter with the Pluto system in the summer of 2015. And according to the team, nine-headed Hydra is a fitting companion for the ninth planet. This summer, the IAU will decide on the much-discussed planetary status of Pluto. The naming of Hydra "could possibly" help convince the IAU to preserve Pluto's planet status.

James Christy, the now-retired discoverer of Charon, says he would have preferred Persephone--Pluto's involuntary spouse--as the name for one of the satellites, but again, that name has already been used for an asteroid. Back in 1978, Christy chose Charon to honour his wife Charlene.

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Posts: 131433
Date:
Additional Satellites
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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, J.R. Spencer

Observations of Pluto and its solar-tidal stability zone were made using the Advanced Camera for Surveys' (ACS) Wide Field Channel (WFC) on the Hubble Space Telescope 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, as discussed by Weaver et al. (2006) and Stern et al. (2006a). Confirming observations of the newly discovered moons were obtained using the ACS in the High Resolution Channel (HRC) mode on 2006 Feb 15 (Mutchler et al. 2006). Both sets of observations provide strong constraints on the existence of any additional satellites in the Pluto system.
Based on the May 2005 observations using the ACS/WFC, the researchers place a 90%-confidence lower limit of m_V = 26.8 (m_V = 27.4 for a 50%-confidence lower limit) on the magnitude of undiscovered satellites greater than 5" (1.1x10^5 km) from Pluto. Using the 2005 Feb 15 ACS/HRC observations researchers place 90%-confidence lower limits on the apparent magnitude of any additional satellites of m_V = 26.4 between 3"-5" (6.9x10^4-1.1x10^5 km) from Pluto, m_V = 25.7 between 1"-3" (2.3x10^4-6.9x10^4 km) from Pluto, and m_V = 24. between 0.3"-1" (6.9x10^3-2.3x10^4 km) from Pluto. The 90%-confidence magnitude limits translate into upper limits on the diameters of undiscovered satellites of 29 km outside of 5" from Pluto, 36 km between 3"-5" from Pluto, 49 km between 1"-3" from Pluto, and 115 km between 0.3"-1" for a comet-like albedo of p_V = 0.04. If potential satellites are assumed to have a Charon-like albedo of p_V = 0.38, the diameter limits are 9 km, 12 km, 16 km, and 37 km, respectively.

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Posts: 131433
Date:
Pluto-Charon System
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Title: On the Orbits and Masses of the Satellites of the Pluto-Charon System
Authors: Man Hoi Lee, S. J. Peale (UCSB)

(UPDATE)

The orbits of the recently discovered satellites of Pluto, S/2005 P2 and S/2005 P1, are significantly non-Keplerian, even if P2 and P1 have negligible masses, because the mass ratio of Charon-Pluto is ~0.1.

Researchers present an analytic theory with P2 and P1 treated as test particles. This analytic theory shows that the azimuthal periods of P2 and P1 are shorter than the Keplerian orbital periods and that the periapse and ascending node of each of the satellites precess at nearly equal rates in opposite directions. The deviation from Kepler's third law is already detected in the unperturbed Keplerian fit of Buie and coworkers.
The researchers also present direct numerical orbit integrations with different assumed masses for P2 and P1 within the ranges allowed by the albedo uncertainties. If the albedos are as high as that of Charon, the masses of P2 and P1 are sufficiently low that their orbits are well described by the analytic theory. There is at present no evidence that P2 has any significant epicyclic eccentricity. However, the orbit of P1 has a significant epicyclic eccentricity, and its prograde periapse precession with a period of 5300 days should be easily detectable.
If the albedos are as low as that of comets, the large inferred masses induce significant variations in the epicyclic eccentricities and/or periapse longitudes on the 400-500-day timescales, due to the proximity of P2 and P1 to the 3:2 mean-motion commensurability. In fact, for the maximum inferred masses, P2 and P1 may be in the 3:2 mean-motion resonance, with the resonance variable involving the periapse longitude of P1 librating. Observations that sample the orbits of P2 and P1 well on the 400-500-day timescales should provide strong constraints on the masses of P2 and P1 in the near future.

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RE: Pluto
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Title: The Positions, Colours, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006
Authors: S.A. Stern, M.J. Mutchler, H.A. Weaver, A.J. Steffl

Pluto's two small satellites, temporarily designated S/2005 P 1 and S/2005 P 2, were observed on four dates (15.1 and 18.1 May 2005, 15.7 February 2006, and 2.8 March 2006) using the Hubble Space Telescope's (HST) Advanced Camera for Surveys (ACS). Here we collect together the astrometric positions of these two satellites (henceforth P1 and P2), as well as a single colour measurement for each satellite and initial constraints on their photometric variability obtained during these observations. We find that both satellites have essentially neutral (grey) reflectivities, like Charon. We also find that neither satellite exhibited strong photometric variation, which might suggest that P1 and P2 are toward the large end of their allowable size range, and therefore may have far lower reflectivities than Charon.



ACS/HRC broad V-band composite image of the Pluto system obtained on 15 February 2006. The image above is the combination of four 475s dithered images drizzled to an output scale of 0.015 arcsec/pixel (smaller than the input HRC detector pixels, which are 0.025 arcsec/pixel). This is the highest-resolution image of the entire Pluto satellite system to date. The complex HRC point spread function and diffraction spikes emanating from Pluto and Charon are evident. All other faint features can be associated with residual star trails or many cosmic rays events that were not completely removed by our processing steps.

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The latest NASA Hubble Space Telescope images of Pluto's two newly discovered satellites reveal that the new moons have the same colour as Charon. All three of Pluto's satellites reflect the Sun's light equally across the visible spectrum and have essentially the same colour as Earth's moon. Pluto, in contrast, has a reddish hue. The common colour of the moons further reinforces the idea that all three moons were born from a single titanic collision between Pluto and another similarly sized Kuiper Belt object billions of years ago. The colour exposures were made on March 2nd in both red (F606W) and blue (F435W) filters using Hubble's Advanced Camera for Surveys. The Pluto team hopes to make further observations in more colour filters to more precisely characterize the moons.



These NASA Hubble Space Telescope images of Pluto were taken on March 2, 2006, using the High Resolution Channel (HRC) of the Advanced Camera for Surveys (ACS). The image on the left was taken through a blue filter (F435W), and the one on the right was taken through a red filter (F606W).
By comparing these two images in detail, astronomers discovered that the surfaces of Pluto's two newly-discovered satellites (S/2005 P 1 and S/2005 P 2, or P1 and P2 for short) have essentially the same colour as Charon's surface. All three satellites have surfaces that reflect sunlight with equal efficiency at all wavelengths, which means they have the same colour as Earth's moon (in the absence of Earth's atmospheric effects, which can alter the apparent colour of our moon).
In contrast, Pluto's surface has a reddish hue. The remarkable similarity in the colours of the satellites supports the idea that they were all created from material stripped from the surface layers of Pluto during the giant impact that created the entire system more than 4 billion years ago.
(Note that the colour schemes used to display the images are not meant to represent the colours of the objects. Rather, a blue intensity scale is used for the image taken through the F435W filter and a red intensity scale is used for the F606W image simply to highlight that the images were obtained through two different filters.)

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Posts: 131433
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RE: Pluto Moons
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Official names for the newly discovered moons of Pluto have been submitted to the International Astronomical Union (IAU) for formal approval.

The pair currently have been nicknames "Boulder" and "Baltimore," in honour of the hometowns of eight of the nine people on the discovery team (and the respective locations where Hubble space telescopes instruments were built and where Hubble scientific institute is located).
S/2005 P1, has been nicknamed "Baltimore." S/2005 P2, being smaller, is "Boulder."

-- Edited by Blobrana at 21:51, 2006-02-27

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Posts: 131433
Date:
Plutos moons
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Astronomers using NASA's Hubble Space Telescope have confirmed the presence of two new moons around the distant planet Pluto. The moons were first discovered by Hubble in May 2005, but the Pluto Companion Search team probed even deeper into the Pluto system with Hubble on February 15 to look for additional satellites and to characterise the orbits of the moons.
In the image, Pluto is in the centre and Charon is just below it. The moons, provisionally designated S/2005 P 1 and S/2005 P 2, are located to the right of Pluto and Charon.


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The confirmation reinforces the emerging view that the Kuiper Belt, a swarm of icy bodies encircling the solar system beyond Neptune, may be more complex and dynamic than astronomers once thought. Pluto resides inside the Kuiper Belt and is about 3 billion miles from the Sun. Pluto was discovered in 1930.
The moons' orbits are in the same plane as the orbit of the much larger satellite Charon (discovered in 1978). This likely means the moons were not captured, but instead were born, along with Charon, in what is commonly theorized to have been a titanic collision between two Pluto-sized objects over 4 billion years ago.
A team of astronomers, led by Hal Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and Alan Stern of the Southwest Research Institute in Boulder, Colorado, made the new observations on Feb. 15, 2006, with Hubble's Advanced Camera for Surveys (ACS).
The team used the sharp vision of the ACS to do a targeted search of the region around and inside the orbits of the twin moons. In addition to confirming the reality of the new moons, the observations also rule out the possibility of other satellites of roughly similar size orbiting Pluto inside the orbits of the two moons. The moons, provisionally designated S/2005 P 1 and S/2005 P 2, are approximately 40,000 and 30,000 miles away from Pluto, respectively.

Astronomers believe that the formation of the Pluto system is similar to that of our Earth and Moon. In both cases a comparable-sized body slammed into the parent planet. Simulations show that debris from the collision would go into an orbit around the planet and coalesce to form one or more satellites. Investigating how Pluto ended up with three moons while the Earth has only one should yield valuable insights into the processes by which satellite systems form around planets.

The team will use Hubble again on March 2 to study the new moons. They hope the follow-up observations will provide information on the moons' colour, as well as their size and shape, which could yield further clues about the formation and evolution of the Pluto system.

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RE: Pluto
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Astronomers have found that Pluto's surface temperature is colder than it should be. It's thought that the planetís lower temperature is the result of interactions between its icy surface and the thin nitrogen atmosphere.

Using the Submillimeter Array, or SMA, a network of radio telescopes located in Hawaii, astronomers found that Plutoís average surface temperature was about 43 K instead of the expected 53 K, which is what the temperature of Charon is.

Unlike Pluto, Charon has no atmosphere, so its surface temperature was what astronomers predicted based on its geological makeup and reflectivity.
Pluto is located thirty times farther away from the Sun than Earth, about three billion miles, and receives only about 1/1000th of the light that our planet receives. Plutoís surface temperature varies widely because of its erratic orbit, which can send it as close as 30 astronomical units (AU), or as far away as 50 AU.
Astronomers have suspected since the early 1990ís that Pluto is colder than it should be, but they were unable to confirm their suspicions until recently because it was difficult to separate the heat emissions of Pluto from nearby Charon.
From Earth, Pluto and Charon appear about 0.9 arcseconds apart.

The SMA is the first telescope able to make the required measurement. Other telescopes like the Very Large Array (VLA) in New Mexico have higher resolution than the SMA, but are less sensitive to colder objects.

"Weíre the first to have the combination of resolution and sensitivity to be able to do this experiment" - Mark Gurwell, astronomer at the Harvard-Smithsonian Centre for Astrophysics and a co-author on the study.

Astronomers think Plutoís colder than expected temperature reading involves interactions between nitrogen ice on the planetís surface and the nitrogen gas that makes up its atmosphere.
The two forms of nitrogen are in a constant state of careful flux: as Pluto moves away from the Sun, the nitrogen gas "condenses," freezing and falling back to the surface as ice. The opposite happens when Pluto is closer to the Sun.
Planets like Venus and Earth experience a natural greenhouse effect, where sunlight energy striking the surface is absorbed and used to heat the surface. On Pluto, the opposite happens.

"Pluto is a dynamic example of what we might call an anti-greenhouse effect" - Mark Gurwell.

Instead of being absorbed and warming the surface, sunlight striking Pluto is used to convert nitrogen ice on its surface into gas. A similar process happens when humans sweat: the evaporation of sweat from the skin has a cooling effect because the evaporated water carries away the bodyís excess heat.
The finding could apply to other planets in the solar system which have condensable atmospheres like Mars, or even to extra solar planets.
In the future, astronomers will be able to make even more precise measurements of Pluto using the Atacama Large Millimetre Array (ALMA) currently being built in Chile. The ALMA is scheduled for completion in 2012 but early scientific experiments could begin as soon as 2008.
The ALMA will allow astronomers to see where on Plutoís surface nitrogen gas is being generated and whether the atmosphere is spread out evenly across the entire planet or concentrated in hot spot like on Saturnís moon, Enceladus.

The new finding will be presented at the 2005 meeting of the American Astronomical Society that begins on January 8 2006 in Washington, D.C.

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