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2003 UB313 (the largest object discovered in the Solar system since Neptune in 1846)

Announced on IAUC 8577 on 29 Jul 2005 with more details given on MPEC 2005-O41 the same day, this extraordinary object had been originally detected as a (very slow) moving object on 5th January 2005, from images taken on 21st October 2003 nearly 15 months previously.

It is slightly larger than Pluto and currently over 96 times further from the Sun than the Earth (or 96 AU) and over three times further away than Pluto. It is the most distant object observed in the Solar System to date, even further than the previous record holder Sedna, discovered by the same team in November 2003 which is just over 88 AU away. 2003 UB313 is now at about at its furthest from the Sun, coming closest to the Sun 250 years from now at a distance of about 38 AU. 

The discoverers M. E. Brown, C. A. Trujillo, and D. Rabinowitz used the Palomar 1.2-m Schmidt telescope and very large field Quest camera (172 Megapixels - 112 CCDs(!) arranged to cover 3.6x4.6 at the focal plane of this famous instrument) in their ongoing search for large distant solar system objects. Other large transneptunian objects discovered by them in the last few years include Sedna, Quaoar, Orcus and 2002 AW197.

Brown had intended to announce 2003 UB313 in September 2005 after completing follow-up observations with other large instruments including the Spitzer Space Telescope. However, concerns that their discovery might be pre-empted by others prompted them to announce their discovery of 2003 UB313 (along with another very large transneptunian object 2005 FY9) and also their observations of another, 2003 EL61 in late July 2005.

The image above shows the object in rather poor sky conditions moving just 40" in a period of 3 days. The field of view is approximately 1/7th the area of the full moon and shows just how slow and distant the object is. For comparison the moon travels the same apparent distance in about 75 seconds of time.

See more information here:

2003 UB313
(90377) Sedna

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