145451 Rumina
Rumina belongs to the scattered disk, the population of TNOs whose orbits have been perturbed by Neptune into eccentric, inclined paths1. A 2018 stellar-occultation prediction by the RECON project lists the object at 37.0 AU from the Sun and 36.0 AU from Earth, with an absolute magnitude H of 4.4 and a dynamical classification of SCATNEAR2.
| Key fact | Detail |
|---|---|
| Diameter | About 705 km; a thermal-model solution gives 524 (+96/−103) km with a geometric albedo of 0.102 (+0.057/−0.029)1 |
| Absolute magnitude | H ≈ 4.42 |
| Dynamical class | Scattered-disk object (SDO); classified SCATNEAR (near-scattered) in the RECON occultation prediction1 • 2 |
| Light curve | Amplitude Δm = 0.12 ± 0.05 mag (Perna et al. 2009)3 |
Orbit and physical properties
Size and albedo. Published size estimates differ because they rest on different methods. A compilation of TNO diameters and albedos lists H = 4.58 with an assumed-albedo diameter of 4.58 (hundreds of km scale) and a geometric albedo of 0.555 ± 0.075 from Perna et al. (2009), alongside a thermal-model solution of 4.52 ± 0.01 in H, a diameter of 524 (+96/−103) km, and an albedo of 0.102 (+0.057/−0.029)1. The spread reflects how little is known about the surface reflectivity of mid-sized TNOs, since diameter and albedo cannot be separated from brightness alone.
Rotation and surface. Photometric monitoring with the New Technology Telescope of the European Southern Observatory at La Silla, part of ESO Large Programme 178.C-0036, yielded a light curve with a small amplitude of Δm = 0.12 ± 0.05 mag3 • 4. A small amplitude indicates a nearly spherical shape or a pole-on viewing geometry, and the rotational period and light curve were used to place a lower limit on the axis ratio and hence estimate the body's density4.
Near-infrared colors confirm that Rumina is a BB-class object in the taxonomy of Centaurs and TNOs, the spectrally neutral to bluish class common among icy bodies3. Later measurements found the V − J and V − H colors about 0.2 mag redder than earlier published values while the V − K color was consistent; because the color differences exceed the light-curve amplitude, the authors suggested possible surface heterogeneity, with regions of differing composition3. Visible spectroscopy obtained on 4 December 2007 in the same ESO large program measured a very shallow spectral slope of 2.2 ± 0.7, consistent with the neutral BB classification5.
Observation opportunities
Because Rumina is large and moderately bright (apparent V magnitude about 20.1 at the 2018 epoch), it is a target for stellar-occultation campaigns, in which the object's shadow crossing a background star measures its size and shape directly2. A predicted occultation event on 24 December 2018 placed the 1-sigma cross-track uncertainty of the shadow at 1,693 km, with the TNO moving 23.7 km/s on the sky relative to the star2.
References
- TNO/centaur diameters, albedos, and densities (Johnston's Archive)
- RECON: TNO occultation event (145451) 05RM43, 2018/12/24
- D. Perna et al.: Colors and taxonomy of Centaurs and trans-Neptunian objects (thesis)
- Perna, D., Dotto, E., Barucci, A., Rossi, A., Fornasier, S., De Bergh, C. (2009). Rotations and densities of trans-Neptunian objects, CNR IRIS record
- Visible spectroscopy of the new ESO large programme on trans-Neptunian objects and Centaurs: final results
Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Kuiper belt and trans-Neptunian objects
Initially written Oct 21, 2026 · Edited: Oct 25, 2026
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