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Sedna has a V band absolute magnitude of about 1.8, and is estimated to have an albedo (reflectivity) of around 0.41, giving it a diameter of approximately 900 km. [14] At the time of discovery it was the brightest object found in the Solar System since Pluto in 1930.
[9] [19] It was initially estimated to be 300 km (190 mi) in diameter under the assumption of an albedo of 0.15, [5] though observations of a single-chord stellar occultation at Penticton, Canada on 20 October 2018 suggested a smaller diameter of 220 km (140 mi), corresponding to a higher albedo of 0.21.
This is close to what as of 2019 is believed to be roughly the limit for objects beyond Neptune that are fully compact, solid bodies, with Salacia ( r = 423 ± 11 km, m = (0.492 ± 0.007) × 10 21 kg) being a borderline case both for the 2006 Q&A expectations and in more recent evaluations, and with Orcus being just above the expected limit. [52]
Many TNOs in the size range of about 400–1000 km have oddly low densities, in the range of about 1.0–1.2 g/cm 3, that are substantially less than those of dwarf planets such as Pluto, Eris and Ceres, which have densities closer to 2. Brown has suggested that large low-density bodies must be composed almost entirely of water ice since he ...
A sednoid is a trans-Neptunian object with a large semi-major axis and a high perihelion, similar to the orbit of the dwarf planet Sedna. The consensus among astronomers is that there are only three objects that are known from this population: Sedna, 2012 VP 113, and 541132 Leleākūhonua (2015 TG 387). [1] All three have perihelia greater than ...
= 2.54 × 10 −2 m/s: kilometre per hour: km/h ≡ 1 km/h = 2. 7 × 10 −1 m/s knot: kn ≡ 1 nmi/h = 1.852 km/h = 0.51 4 m/s knot (Admiralty) kn ≡ 1 NM (Adm)/h = 1.853 184 km/h [29] = 0.514 77 3 m/s mach number: M: Ratio of the speed to the speed of sound [note 1] in the medium (unitless). ≈ 340 m/s in air at sea level ≈ 295 m/s in air ...
This far infrared radiation is so dim that the thermal method is only applicable to the largest KBOs. For the majority of (small) objects, the diameter is estimated by assuming an albedo. However, the albedos found range from 0.50 down to 0.05, resulting in a size range of 1,200–3,700 km for an object of magnitude of 1.0. [24]
This is a list of trans-Neptunian objects (TNOs), which are minor planets in the Solar System that orbit the Sun at a greater distance on average than Neptune, that is, their orbit has a semi-major axis greater than 30.1 astronomical units (AU).