55637 Uni
Uni and Tinia as seen by the Hubble Space Telescope | |
| Discovery | |
|---|---|
| Discovered by | Spacewatch (291) |
| Discovery site | Kitt Peak National Obs. |
| Discovery date | 30 October 2002 |
| Designations | |
Designation | (55637) Uni |
| Pronunciation | /ˈjuːnaɪ/ |
Named after | Uni |
| 2002 UX25 | |
| Cubewano (MPC) Extended (DES) | |
| Orbital characteristics | |
| Epoch 5 May 2025 (JD 2460800.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 33.35 yr (12,182 days) |
| Earliest precovery date | 12 October 1991 |
| Aphelion | 49.291 AU |
| Perihelion | 36.716 AU |
| 43.003 AU | |
| Eccentricity | 0.1462 |
| 282.01 yr (103,005 days) | |
Average orbital speed | 4.54 km/s |
| 309.49° | |
| 0° 0m 12.24s / day | |
| Inclination | 19.400° |
| 204.57° | |
| ≈ 5 September 2066 ±3 days | |
| 275.27° | |
| Known satellites | 1 (Tinia) |
| Physical characteristics | |
| 659±38 km | |
| Mass | (1.25±0.03)×1020 kg |
Mean density | 0.82±0.11 g/cm3 (assuming equal densities for primary and satellite) 0.80±0.13 g/cm3 |
| 0.075 m/s2 | |
| 0.227 km/s | |
| 14.382±0.001 h | |
| Albedo | 0.107+0.005 −0.008 0.1±0.01 |
| Temperature | ≈ 43 K |
Spectral type | B–V=1.007±0.043 V−R=0.540±0.030 V−I=1.046±0.034 |
| 19.8 | |
| 3.87±0.02, 4.0 | |
55637 Uni (provisional designation 2002 UX25) is a large trans-Neptunian object that orbits the Sun in the Kuiper belt beyond Neptune. It briefly garnered scientific attention when it was found to have an unexpectedly low density of about 0.82 g/cm3. It was discovered on 30 October 2002, by the Spacewatch program.
Uni has an absolute magnitude of about 4.0, and Spitzer Space Telescope results estimate it to be about 660 km in diameter. The low density of this and many other mid-sized TNOs implies that they have never compressed into fully solid bodies, let alone differentiated or collapsed into hydrostatic equilibrium, and so are not likely to be dwarf planets.
Uni has one known moon, Tinia, discovered in 2005.