(24835) 1995 SM55

Lore & Background

1995 SM55 has a high geometric albedo of 0.80 in visible light and a similar orbit to the dwarf planet Haumea, which means that it must be a member of the Haumea family. 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. Members of the Haumea family include 1996 TO66, 2002 TX300, 2003 OP32 and 2005 RR43. 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 123.3 m/s.

Because 1995 SM55 has a high albedo, it appears much brighter than other Kuiper belt objects. Because of its high brightness, astronomers initially believed that 1995 SM55 could have a very large size, with a diameter up to 700 km (430 mi) if it had a dark, low-albedo surface. However, further analysis of 1995 SM55's thermal emission and orbit showed that it should be much smaller with a more reflective surface. On 25 February 2024, 1995 SM55 passed in front of a star and occulted it. This stellar occultation was observed by numerous astronomers at 40 different locations, with 7 of them reporting positive detections of the occultation. The occultation observations revealed that 1995 SM55 is a roughly elliptical object that is 212 km × 184 km × 152 km (132 mi × 114 mi × 94 mi) in diameter (volume-equivalent diameter 181 km or 112 mi). The object has a high geometric albedo of 0.80±0.04.

As of January 2025, this minor planet has not been named by the Minor Planet Center. Suggestions for names are open to the public.

Reader's Guide

The significance of (24835) 1995 SM55 lies in its membership in the Haumea family, a group of icy fragments believed to have originated from a giant collision with the dwarf planet Haumea over 4 billion years ago. Its high geometric albedo of 0.80 and water ice-rich composition are typical of this family, providing evidence for the collisional origin of these objects. The stellar occultation observed on 25 February 2024, with positive detections from 7 of 40 observation locations, allowed astronomers to determine its elliptical shape and volume-equivalent diameter of 181 km, resolving earlier uncertainties about its size. The object's legacy includes refining models of the Haumea family's formation and dynamics, as its ejection speed of 123.3 m/s from Haumea helps constrain the collision scenario. As an unnamed minor planet as of January 2025, it also represents an opportunity for public engagement in naming celestial bodies.

Did You Know?

• 1995 SM55 was discovered on 19 September 1995 by American astronomer Nichole Danzl at Kitt Peak National Observatory.
• It has a geometric albedo of 0.80±0.04, making its surface highly reflective.
• A stellar occultation on 25 February 2024 revealed its dimensions as 212 km × 184 km × 152 km.
• It was likely ejected from the dwarf planet Haumea at a speed of 123.3 m/s.