(26308) 1998 SM165

Lore & Background

1998 SM165 is classified as a twotino by the Deep Ecliptic Survey, meaning it orbits the Sun in a 1:2 resonance with Neptune: for every one orbit of the object, Neptune completes two. Its semi-major axis lies near the edge of the classical Kuiper belt. Observations with the infrared Spitzer Space Telescope and orbits from the Hubble Space Telescope allowed an estimate of its density at 0.51+0.29−0.14 g/cm³, similar to the binary plutino 47171 Lempo and Saturn's moon Hyperion. This low density suggests a highly porous composition dominated by ice. The object is fairly red, with a color comparable to 79360 Sila–Nunam. On 22 December 2001, a minor-planet moon was discovered by American astronomers Michael Brown and Chad Trujillo using the Hubble Space Telescope, announced in January 2002. The satellite measures approximately 96 ± 12 km in diameter and orbits its primary at a distance of 11,310 ± 110 km, completing one orbit in 130.1 ± 1 days, assuming a circular orbit. The minor planet was numbered by the Minor Planet Center on 5 July 2001; as of 2025, it has not been named.

Reader's Guide

The significance of (26308) 1998 SM165 lies in its classification as a twotino, a resonant trans-Neptunian object locked in a 1:2 orbital resonance with Neptune, which helps constrain models of solar system evolution and migration. Its binary nature, with a moon discovered in 2001, provides a rare opportunity to measure physical properties such as density. The estimated density of 0.51+0.29−0.14 g/cm³, derived from Spitzer and Hubble data, is exceptionally low, indicating a highly porous, ice-dominated interior. This density is comparable to other icy bodies like Saturn's moon Hyperion and the binary plutino 47171 Lempo, suggesting a common origin or composition among such objects. The object's red color, similar to 79360 Sila–Nunam, adds to the understanding of surface compositions in the Kuiper belt. As of 2025, it remains unnamed, highlighting the ongoing process of cataloging and characterizing distant solar system bodies.

Did You Know?

• 1998 SM165 is a twotino, meaning it orbits the Sun once for every two orbits of Neptune.
• Its moon was discovered on 22 December 2001 by Michael Brown and Chad Trujillo using the Hubble Space Telescope.
• The object's estimated density is 0.51+0.29−0.14 g/cm³, similar to Saturn's moon Hyperion.
• As of 2025, this minor planet has not been named.