(26308) 1998 SM165
Trans-Neptunian binary
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(26308) 1998 SM165 is a resonant trans-Neptunian object and binary system from the Kuiper belt in the outermost regions of the Solar System. It was discovered on 16 September 1998, by American astronomer Nichole Danzl at the Kitt Peak National Observatory in Arizona.[1] It is classified as a twotino and measures approximately 280 kilometers in diameter. Its minor-planet moon was discovered in 2001.[5]
Hubble Space Telescope image of 1998 SM165 and its companion, taken in December 2001 | |
| Discovery[1] | |
|---|---|
| Discovered by | N. Danzl |
| Discovery site | Kitt Peak Obs. |
| Discovery date | 16 September 1998 |
| Designations | |
| (26308) 1998 SM165 | |
| 1998 SM165 | |
| TNO[2] · twotino[3][4][5] Kozai · distant[1] | |
| Orbital characteristics[2] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 2 | |
| Observation arc | 32.26 yr (11,784 days) |
| Earliest precovery date | 12 October 1982 |
| Aphelion | 64.968 AU |
| Perihelion | 29.866 AU |
| 47.417 AU | |
| Eccentricity | 0.3701 |
| 326.52 yr (119,261 days) | |
| 47.484° | |
| 0° 0m 10.8s / day | |
| Inclination | 13.521° |
| 183.21° | |
| 130.22° | |
| Known satellites | 1[5] (96±12 km in diameter)[6] |
| Physical characteristics | |
| Dimensions | 268±28 km (derived)[5] 287±36 km[6] |
| Mass | (6.87±0.018)Ã1018 kg[5] |
Mean density | 0.51+0.29 â0.14 g/cm3[6] |
| 8.40±0.05 h[6] | |
| 0.07±0.02[6] | |
| 5.7[2] | |
Twotino
1998 SM165 has a semi-major axis (average distance from the Sun) near the edge of the classical belt. The Deep Ecliptic Survey (DES) list this trans-Neptunian object as a twotino that stays in a 1:2 orbital resonance with the planet Neptune (for every one orbit that a twotino makes, Neptune orbits twice).[3][4]
Physical characteristics
The observations with the infrared Spitzer Space Telescope combined with the orbits established using the Hubble Space Telescope allow the estimation of the density, assuming the components of equal albedo.
The resulting estimate of 0.51+0.29
â0.14 g/cm3[6]
is similar to the density of the binary plutino 47171 Lempo (0.3â0.8 g/cm3[7]) and Saturn's moon Hyperion (0.567±0.102 g/cm3[8])
Such a low density is indicative of a highly porous composition dominated by ice.[6]
1998 SM165 is fairly red, with a color comparable to 79360 SilaâNunam.
Satellite
On 22 December 2001, a minor-planet moon was discovered by American astronomers Michael Brown and Chad Trujillo using the Hubble Space Telescope.[5] The discovery was announced in January 2002. The satellite measures approximately 96 ± 12 km (59.7 ± 7.5 mi) in diameter and orbits its primary at a distance of 11,310 ± 110 km (7,028 ± 68 mi). Assuming a circular orbit, this takes 130.1±1 days to complete one orbit.[5]
Numbering and naming
This minor planet was numbered by the Minor Planet Center on 5 July 2001.[9] As of 2025, it has not been named.[1]
