1998 WW31

1998 WW31, is a non-resonant trans-Neptunian object and binary system from the Kuiper belt located in the outermost region of the Solar System, approximately 148 kilometers (92 miles) in diameter. It was first observed on 18 November 1998, by American astronomer Marc Buie and Robert Millis at the Kitt Peak National Observatory in Arizona, United States.[2][3][1] In December 2000, a minor-planet moon, designated S/2000 (1998 WW31) 1 with a diameter of 123 kilometers (76 miles), was discovered in its orbit.[7] After Charon in 1978, it was the first of nearly 100 satellites since discovered in the outer Solar System.[3][7]

1998 WW31
Hubble Space Telescope image of 1998 WW31 and its satellite in orbit
Discovery[1]
Discovered byM. W. Buie[2]
R. L. Millis[3]
Discovery siteKitt Peak Obs.
Discovery date18 November 1998
(first observed only)
Designations
1998 WW31
TNO[2][4] · cubewano (hot)[5]
distant[1] · binary[6]
Orbital characteristics[4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 4
Observation arc20.94 yr (7,647 d)
Aphelion48.526 AU
Perihelion40.429 AU
44.477 AU
Eccentricity0.09102
296.63 yr (108,345 d)
141.847°
0° 0m 11.963s / day
Inclination6.8171°
237.138°
51.218°
Known satellites1 (D: 123 km; P: 587 d)[6][7]
Physical characteristics
Mean diameter
148 km (est. primary)[5][6]
192.1 km (cal. system)[8]
0.04 (est.)[9]
0.10 (assumed)[8]
blue[9]
C (assumed)[8]
V–I = 0.910±0.020[10]
6.7[4][8]
6.9[9]

    Orbit and classification

    Located beyond the orbit of Neptune, 1998 WW31 is a non-resonant classical Kuiper belt object (cubewano) of the so-called hot population, which have higher inclinations than those of the cold population.[5][11] It orbits the Sun at a distance of 40.4–48.5 AU once every 297 years (108,345 days; semi-major axis of 44.48 AU). Its orbit has an eccentricity of 0.09 and an inclination of 7° with respect to the ecliptic.[4] The body's observation arc begins at Kitt Peak with its first observation on 18 November 1998.[1]

    Numbering and naming

    As of 2018, this minor planet has not been numbered nor named by the Minor Planet Center.[1]

    Physical characteristics

    1998 WW31 is expected to have a low albedo due to its blue (neutral) color.[9] Other sources assume a higher albedo of 0.10 and 0.16, respectively (see below).[6][8] It has a V–I color index of 0.91,[10] notably lower than the mean-color index for cubewanos, and in between that of comets and Jupiter trojans.[12]: 35 

    Hubble image composite from 2001–02 of 1998 WW31 with its satellite on a long, 587-day orbit

    Satellite

    1998 WW31 is a binary minor planet with a minor-planet moon in its orbit. On 22 December 2000, French astronomers Christian Veillet and Alain Doressoundiram in collaboration with J. Shapiro discovered the satellite using the Canada–France–Hawaii Telescope at Mauna Kea on the Big Island of Hawaii, United States. The discovery was announced on 16 April 2001 and received the provisional designation S/2000 (1998 WW31) 1.[7]

    It was the first trans-Neptunian binary discovered after Charon in 1978, the largest satellite in the Pluto–Charon system.[3] Since then nearly 100 trans-Neptunian binaries have been discovered. 1998 WW31 is also one of the most symmetrical binaries known in the Solar System. The satellite has a highly eccentric orbit of approximately 0.8 with an exceptionally long orbital period of 587 days and a semi-major axis of 22,620 kilometers.[3][6]

    Diameter and albedo

    While the primary measures 148 kilometers, the satellite has a diameter of 123 kilometers (a ratio of 0.883) with a combined system diameter of 192 kilometers.[6][11] The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.10 and calculates a system diameter of 192 kilometers based on an absolute magnitude of 6.7,[8] while Mike Brown finds a diameter of 267 kilometers with a lower albedo of 0.04.[9]

    Rotation period

    As of 2020, no rotational lightcurve of 1998 WW31 has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.[8][11]

    References
    1. "1998 WW31". Minor Planet Center. Retrieved 10 October 2018.
    2. "List Of Transneptunian Objects". Minor Planet Center. Retrieved 10 October 2018.
    3. "The binary Kuiper-belt object 1998 WW31" (PDF). Nature. 18 April 2002. Retrieved 10 October 2018.
    4. "JPL Small-Body Database Browser: (1998 WW31)" (2011-12-24 last obs.). Jet Propulsion Laboratory. Retrieved 10 October 2018.
    5. Johnston, Wm. Robert (30 December 2017). "List of Known Trans-Neptunian Objects". Johnston's Archive. Retrieved 10 October 2018.
    6. Johnston, Wm. Robert (31 January 2015). "Asteroids with Satellites Database – 1998 WW31 and S/2000 (1998 WW31) 1". Johnston's Archive. Retrieved 10 October 2018.
    7. Veillet, C.; Doressoundiram, A.; Shapiro, J.; Kavelaars, J. J.; Morbidelli, A. (April 2001). "S/2000 (1998 WW_31) 1". IAU Circ. 7610 (7610): 1. Bibcode:2001IAUC.7610....1V. Retrieved 10 October 2018.
    8. "LCDB Data for (1998 WW31)". Asteroid Lightcurve Database (LCDB). Retrieved 10 October 2018.
    9. Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 10 October 2018.
    10. Hainaut, O. R.; Boehnhardt, H.; Protopapa, S. (October 2012). "Colours of minor bodies in the outer solar system. II. A statistical analysis revisited". Astronomy and Astrophysics. 546: 20. arXiv:1209.1896. Bibcode:2012A&A...546A.115H. doi:10.1051/0004-6361/201219566. S2CID 54776793.
    11. "Asteroid 1998 WW31". Small Bodies Data Ferret. Retrieved 10 October 2018.
    12. Fornasier, S.; Dotto, E.; Hainaut, O.; Marzari, F.; Boehnhardt, H.; De Luise, F.; et al. (October 2007). "Visible spectroscopic and photometric survey of Jupiter Trojans: Final results on dynamical families". Icarus. 190 (2): 622–642. arXiv:0704.0350. Bibcode:2007Icar..190..622F. doi:10.1016/j.icarus.2007.03.033. S2CID 12844258.
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