Dwarf planet candidates

You may have heard the term being bandied about, but really, what is a dwarf planet? It refers to a category created by the International Astronomers’ Union (IAU) used to describe particular celestial bodies.

There are only 5 dwarf planets: Ceres, Makemake, Eris, Pluto and Haumea. Dwarves are celestial bodies large enough to take spherical form, orbit around the sun but aren’t satellites in themselves. A “full-size” planet has succeeded in clearing its orbit of debris and other objects while a dwarf has not. While there are only 5 dwarf planets, the list of dwarf planet candidates is considerably longer.

The list of candidates that make the curious wonder what is a dwarf planet is based on absolute magnitude (H). H is “the apparent magnitude an object would have if it were 1 astronomical unit (au) away from the sun and the observer and located at a phase angle of zero degrees”. A lower H-value indicates a larger theoretical minimum diameter (TMD) of the object.

The number of dwarf planet candidates with an H-value less than 3 is few. The H-value indicates a TMD greater than 333km: Sedna, 2007 OR10, Orcus, and Quaoar. An H-value of 3-4 is given to candidates whose TMD is 210-330km: (55636) 2002 TX300, Vesta, Ixion, (55565) 2002 AW197, 2005 QU182, (202421) 2005 UQ513, 2007 UK126, (55637) 2002 UX25, (174567) 2003 MW12, Varuna, 2002 MS4, 2006 QH181, (84522) 2002 TC302, (145452) 2005 RN43, (90568) 2004 GV9, (42301) 2001 UR163.

There are also candidates with H-values of 4-5: (145453) 2005 RR43, (84922) 2003 VS2, (208996) 2003 AZ84, 2004 XA192, 2009 YE7, Pallas, (120178) 2003 OP32, (120347) 2004 SB60, 2003 UZ413, (120348) 2004 TY364, 2008 ST291, (145451) 2005 RM43, 2004 NT33, 2004 XR190 (Buffy), (119951) 2002 KX14, (144897) 2004 UX10, (19308) 1996 TO66, 2004 PR107, 2001 QF298, (26375) 1999 DE9, 38628 Huya, (145480) 2005 TB190, (175113) 2004 PF115, (47171) 1999 TC36, 2007 JH43, 2003 QX113, (24835) 1995 SM55, (120132) 2003 FY128, (82075) 2000 YW134, 19521 Chaos, 2002 XV93, 2002 CY248, 2007 JJ43, 2008 OG19, 2000 CN105. Candidates with H-values above 5: (119979) 2002 WC19, (79360) 1997 CS29, 1999 CD158, 2006 HH123, (15874) 1996 TL66, 2003 QW90, Hygeia, 2002 KW14, (35671) 1998 SN165.

It is thought there might be up to 2000 dwarves to be identified and named once the Kuiper belt and the region beyond it is explored.

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