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TOPIC: 2003UB313 / The Tenth Planet
Blobrana


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Dwarf planet (136199) Eris
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Title: A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation
Authors: B. Sicardy, J. L. Ortiz, M. Assafin, E. Jehin, A. Maury, E. Lellouch, R. Gil Hutton, F. Braga-Ribas, F. Colas, D. Hestroffer, J. Lecacheux, F. Roques, P. Santos-Sanz, T. Widemann, N. Morales, R. Duffard, A. Thirouin, A. J. Castro-Tirado, M. Jelínek, P. Kubánek, A. Sota, R. Sánchez-Ramírez, A. H. Andrei, J. I. B. Camargo, D. N. da Silva Neto et al.

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. Read more



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Faraway Eris is Pluto's Twin

Astronomers have accurately measured the diameter of the faraway dwarf planet Eris for the first time by catching it as it passed in front of a faint star. This event was seen at the end of 2010 by telescopes in Chile, including the Belgian TRAPPIST telescope at ESO's La Silla Observatory. The observations show that Eris is an almost perfect twin of Pluto in size. Eris appears to have a very reflective surface, suggesting that it is uniformly covered in a thin layer of ice, probably a frozen atmosphere. The results will be published in the 27 October 2011 issue of the journal Nature.
In November 2010, the distant dwarf planet Eris passed in front of a faint background star, an event called an occultation. These occurrences are very rare and difficult to observe as the dwarf planet is very distant and small. The next such event involving Eris will not happen until 2013. Occultations provide the most accurate, and often the only, way to measure the shape and size of a distant Solar System body.
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Blobrana


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RE: 2003UB313 / The Tenth Planet
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Dwarf Planet 136199 Eris is at Opposition (95.606 AU) on the 15th October, 2011.



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Blobrana


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Dwarf planet (136199) Eris
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Title: Size, density, albedo and atmosphere limit of dwarf planet Eris from a stellar occultation
Authors: B. Sicardy, J. L. Ortiz, M. Assan, E. Jehin, A. Maury, E. Lellouch R. Gil-Hutton  F. Braga-Ribas, F. Colas, J. Lecacheux, F. Roques, P. Santos-Sanz, T. Widemann, N. Morales, A. Thirouin, J. I. B. Camargo, R. Vieira-Martins, M. Gillon, J. Manfroid, R. Behrend, and the Eris occultation team

We report the observation of a multi-chord stellar occultation by the dwarf planet (136199) Eris. The event was observed on November 6, 2010 UT, from two sites in Chile. Our observation is consistent with a spherical Eris with radius RE =1163± 6 km, density =2.52 ±0.05 g cm^-3 , and visible geometric albedo pV =0.96 +0.09  _-0.04 . Besides being remarkably similar in size to Pluto, Eris appears as one of the intrinsically brightest objects of the solar system, with a density suggesting a mainly rocky interior. Upper limits of about 1 nbar are derived for the surface pressure of possible nitrogen, argon or methane atmospheres of the dwarf planet.

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Dysnomia
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Dysnomia, officially (136199) Eris I Dysnomia, is the only known moon of the dwarf planet Eris (the most-massive known dwarf planet in the Solar System). It was discovered on the 10th September, 2005, by Mike Brown and the laser guide star adaptive optics team at the W. M. Keck Observatory, and carried the provisional designation of S/2005 (2003 UB313) 1 until officially named Dysnomia (from the Ancient Greek word meaning "lawlessness") after the daughter of the Greek goddess Eris.



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RE: 2003UB313 / The Tenth Planet
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The death of the 10th planet

 At the time of the Pluto vote, my discovery was still officially called only by its license plate number of 2003 UB313, but to many it was known by the tongue-in-cheek nickname of Xena, and to even more it was known simply as the tenth planet. Or maybe, after today, not the tenth planet. Xena had precipitated the past year of intensive arguments about Pluto, but it was clear that Xena would also share whatever fate was dealt to Pluto. If Pluto was to be a planet, then so too Xena. If Pluto was to be kicked out, Xena would get the same boot. It was worth waking up early to find out the answer.
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136199 Eris
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Discovery of dwarf planet Eris announced on July 29, 2005

Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly.
Eris was discovered by the team of Mike Brown, Chad Trujillo, and David Rabinowitz on January 5, 2005, from images taken on October 21, 2003. The discovery was announced on July 29, 2005, the same day as Makemake and two days after Haumea.
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RE: 2003UB313 / The Tenth Planet
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Is Eris bigger than Pluto or vice-versa?

In November, that object, now known as the dwarf planet Eris, passed in front of a dim, distant star. Astronomers led by Bruno Sicardy of the Paris Observatory measured how long the star disappeared behind Eris and from that, calculated the width of Eris.
The occultation measurement - which means Eris is not just smaller than expected but also incredibly shiny - is the latest surprise of the Kuiper Belt, a ring of icy debris beyond Neptune. That belt turns out to be even stranger than astronomers thought a few years ago. Not everyone is convinced that Eris is smaller than Pluto. Brown is perplexed. The occultation measurement seems to demonstrate that Eris' diameter is less than 2,360 kms, or 1,466 miles, Brown said.
That is smaller than earlier estimates of 3,000 kms, based on infrared light from Eris, and 2,400 km, based on Brown's observations with the Hubble Space Telescope. But he notes that conflicting figures for the size of Pluto appear on websites.
Wikipedia, citing a 2006 paper, puts the diameter at 2,306 kms, give or take 20 kms.
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Dwarf planet Eris
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Dwarf planet Eris may be smaller than Pluto after all

The dwarf planet Eris - once thought to be the largest body in the solar system beyond Neptune's orbit - may actually be smaller than Pluto, new observations suggest.
Three teams of astronomers watched through telescopes as the icy Eris passed in front of a distant star over the weekend. The length of the occultation - as the event is called - showed that Eris is likely less than 1,454 miles (2,340 kilometres) wide, the magazine Sky & Telescope reported.
This would make Eris a smidge smaller than Pluto, which is about 1,455 miles (2,342 km) wide.
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Occultation by dwarf planet Eris (Nov-6th-2010)



Occultation of a 16 magnitude star by dwarf planet Eris on November 6th, 2010. The observation was performed with a 40 cm. robotic telescope from The Andalusian Astrophysics Institute (Instituto de Astrofísica de Andalucía, Spain), located at San Pedro de Atacama (Chile). The star can be seen centred in the field, where the arrow is pointing, and it clearly shows how it disappears beneath Eris shadow, and how it shortly emerges afterwards. This occultation will allow to determine very precisely the size of the object. Eris is a trans-Neptunian object and the most distant object for which such an occultation has been detected, being at 96.6 Astronomical Units at the moment at which the occultation occurred.

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