1995 SM55 has a high geometric albedo of 0.67 in visible light and a similar orbit to the dwarf planetHaumea, which means that it must be a member of the Haumea family.[3][8] The Haumea family is a population of bright, water ice-rich Kuiper belt objects that are believed to have broken off from Haumea after a giant collision over 4 billion years ago.[17][16] Members of the Haumea family include 1996 TO66, 2002 TX300, 2003 OP32 and 2005 RR43.[17][16] Based on the differences between the orbits of 1995 SM55 and Haumea, the object was likely ejected from the dwarf planet at a relatively high speed of 123.3m/s.[16]
Physical characteristics
Because 1995 SM55 has a high albedo, it appears much brighter than other Kuiper belt objects.[18] Because its high brightness, astronomers initially believed that 1995 SM55 could have a very large size, with a diameter up to 700km (430mi) if it had a dark, low-albedo surface.[19] However, further analysis of 1995 SM55's thermal emission and orbit showed that it should be much smaller with a more reflective surface.[18]
On 25 February 2025, 1995 SM55 passed in front of a star and occulted it.[8] This stellar occultation was observed by numerous astronomers at 40 different locations, with 5 of them reporting positive detections of the occultation.[8] The occultation observations revealed that 1995 SM55 is a roughly elliptical object that is 218km ×180km (135mi ×112mi) in diameter (area-equivalent diameter198km or 123mi).[8]
↑ JPL Horizons Observer Location: @sun (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 3-sigma.)
1 2 John Stansberry; Will Grundy; Mike Brown; Dale Cruikshank; John Spencer; David Trilling; etal. (2007). Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope. arXiv:astro-ph/0702538. Bibcode:2008ssbn.book..161S.
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