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TOPIC: Pluto


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RE: Pluto
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plutochart

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Whether you call it a planet or not, Pluto has officially been overtaken by a more massive planetary object Eris (previously nicknamed Xena).
Pluto, traditionally known as the ninth planet of our Solar System, sits in a giant zone called the Kuiper belt that is filled with asteroids and many other planetary bodies. The discovery of more and more objects in this zone including Eris, in 2005, which was found to be bigger than Pluto led astronomers to try to more strictly define what is and isn't a planet. In 2006, members of the International Astronomical Union (IAU) at a meeting in Prague, the Czech Republic, voted that Pluto be reclassified as a 'dwarf planet'. Eris, by these terms, sits in the same category.

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"Why isn't Pluto a planet any more?"
Answered by Dr. Robert Hurt of NASA's Spitzer Science Centre
Windows Media: 56k | Broadband

Transcript (PDF)

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Constraints on Rings in the Pluto System
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Title: First Constraints on Rings in the Pluto System
Authors: A.J. Steffl, S.A. Stern
(revised v2)

Simple theoretical calculations have suggested that small body impacts onto Pluto's newly discovered small satellites, Nix and Hydra, are capable of generating time-variable rings or dust sheets in the Pluto system. Using HST/ACS data obtained on 2006 February 15 and 2006 March 2, we find no observational evidence for such a ring system and present the first constraints on the present-day I/F and optical depth of a putative ring system. At the 1500-km radial resolution of our search, we place a 3-sigma upper limit on the azimuthally-averaged normal I/F of ring particles of 5.1x10^-7 at a distance of 42,000 km from the Pluto-Charon barycentre, the minimum distance for a dynamically stable ring (Stern et al., 1994; Nagy et al., 2006); 4.4x10^-7 at the orbit of Nix; and 2.5x10^-7 at the orbit of Hydra. For an assumed ring particle albedo of 0.04 (0.38), these I/F limits translate into 3-sigma upper limits on the normal optical depth of macroscopic ring particles of 1.3x10^-5 (1.4x10^-6), 1.1x10^-5 (1.2x10^-6), 6.4x10^-6 (6.7x10^-7), respectively. Were the New Horizons spacecraft to fly through a ring system with optical depth of 1.3x10^-5, it would collide with a significant number of potentially damaging ring particles. We therefore recommend that unless tighter constraints can be obtained, New Horizons cross the putative ring plane within 42,000 km of the Pluto-Charon barycentre, where rings are dynamically unstable. We derive a crude estimate of the lifetime of putative ring particles of 900 years.

plutosystem v3

Drizzled HRC F606Wimages of the Pluto system. The image on the left is from the 2006 February 15 visit, while the image on the right is from the 2006 March 2 visit. Pluto, Charon, Nix, and Hydra can be clearly seen. All other features are due to the extended PSF halos around Pluto and Charon or artefacts introduced by the incomplete removal of background star trails or cosmic ray events. The diffraction spikes from Pluto have been used to divide each image into four quadrants. 1500 km width annuli at the orbital distances of Nix (left) and Hydra (right) are shown in red. Four 10° segments (half width), centred on each diffraction spike, are excluded from analysis. A one arcsecond scale bar is shown in the upper left of each image.

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(134340) Pluto
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Pluto is now officially named (134340) Pluto.

(134340) Pluto 1930 01 23 C. W. Tombaugh, Flagstaff
(136199) 2003 UB313 2003 10 21 M. E. Brown, C. A. Trujillo, D. Rabinowitz, Palomar
(136472) 2005 FY9 2005 03 31 M. E. Brown, C. A. Trujillo, D. Rabinowitz, Palomar
(136108) 2003 EL61 2003 03 07 F. J. Aceituno, P.Santos Sanz, J.L. Ortiz, Sierra Nevada

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Astronomers have approved the historic new planet definition guidelines today, and downsizing Earth's neighbourhood from nine principal heavenly bodies to eight by demoting Pluto.

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An international panel has unanimously recommended that Pluto retain its title as a planet, and it may be joined by other undersized objects that revolve around the sun.
Some astronomers had lobbied for reclassifying Pluto because it is so tiny. And at least one major museum has excluded Pluto from its planetary display. But sources tell NPR that under a proposal to be presented at a big meeting of astronomers in Prague next week for a vote, Pluto would become part of a new class of small planets. Several more objects could be granted membership.

When Pluto was first discovered in 1930, its planethood was not in question. Early estimates put it at perhaps five times the size of the Earth. Over the years, measurements have consistently shrunk.

Under a new proposal, to be presented at a big meeting of astronomers in Prague next week for a vote, Pluto would become part of a new class of small planets and several more objects could be granted membership.
Several panel members have favoured dividing planets into categories: terrestrial planets (Mercury, Venus, Earth, Mars), giant planets (Jupiter, Saturn, Uranus, Neptune) and a third class that would include Pluto.

"We'll call them dwarf planets or something" - Iwan Williams, an astronomer at the University of London.

Source NPR

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Hydra
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On the night of 5/6 August 2006, the newly discovered Pluto satellite Hydra (alias 2005/P1) will occult a star, 2UCAC 26034796, with magnitudes respectively

mK = 12.7 , mH = 12.9, mJ = 13.7, mI =14.8, (rUCAC = 16.2) mV = 16.5.

portHydra-2006-8-6-0h10m

This rare event might be seen from somewhere in Spain, Portugal (00h04), or Canary Islands (00h05), or Africa and South America (00h13). The faintness of the star requires a large enough telescope and a sensitive camera. The star and Hydra will be about 3 arcsec south of Pluto (mK = 12.9, mV = 13.9) : it is a MUST to resolve the images of Pluto and the star on different pixels.

060806occHydra

Depending on Hydra's albedo (m = 22.9), the satellite brightness implies a diameter ranging from 50 to 150 km, i.e. a poorly constrained size. Observing such occultation would provide constraints on the satellite size, an important step in determining its albedo, hence its nature (bright icy body vs dark cometary material) and origin. Size can also constrain Hydra's mass, with important consequences for better estimating its resonant interaction with Nix

Source

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RE: Pluto
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Astronomers at the University of Tasmania have found that the solar system's smallest planet is not getting colder as first thought and it probably does not have rings.

Dr John Greenhill has collected observations from last month's event when Pluto passed in front of a bright star, making it easier to study.
French scientists have shared the measurements they took in Tasmania that night, which indicate that the planet is unlikely to have rings.

Dr Greenhill says the results are surprising because they show Pluto is warming up.

"It looks as though the atmosphere has not changed from 2002, which is pretty surprising because we expected the atmosphere would freeze out as the planet moved further away from the Sun. But so far, if anything, the atmosphere has gotten even denser." - Dr John Greenhill.

Source

-- Edited by Blobrana at 10:35, 2006-07-26

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Nix and Hydra
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Nix and Hydra photographed by Hubble in 2005


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