(85713) 1998 SS49

(85713) 1998 SS49, provisional designation 1998 SS49, is an asteroid on an eccentric orbit, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 3 kilometers (1.9 miles) in diameter. The asteroid was discovered on 29 September 1998, by astronomers of the LINEAR program at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.[2] It is one of the largest potentially hazardous asteroids and has a notably low Earth-MOID of less than the distance to the Moon.[12]

(85713) 1998 SS49
Discovery[1]
Discovered byLINEAR
Discovery siteLincoln Lab's ETS
Discovery date29 September 1998
Designations
(85713) 1998 SS49
1998 SS49
Apollo · NEO · PHA[1][2]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc18.05 yr (6,593 days)
Aphelion3.1535 AU
Perihelion0.6940 AU
1.9237 AU
Eccentricity0.6393
2.67 yr (975 days)
359.74°
0° 22m 9.84s / day
Inclination10.764°
41.493°
102.47°
Earth MOID0.0023 AU · 0.9 LD
Physical characteristics
Dimensions2.00±0.06 km[3]
2.25 km (calculated)[4]
3.03±1.49 km[5]
3.484±0.789 km[6][7]
5.370±0.005 h[8][lower-alpha 1]
5.398±0.001 h[9]
5.66±0.01 h[10][lower-alpha 2]
0.076±0.039[6][7]
0.08±0.12[5]
0.20 (assumed)[4]
0.237±0.018[3]
S (assumed)[4]
15.6[1][4] · 15.70[3][7] · 15.80±0.29[11] · 16.01[5]

    Orbit and classification

    1998 SS49 is a member of the dynamical Apollo group,[1][2] which are Earth-crossing asteroids. Apollo asteroids are the largest subgroup of near-Earth objects.

    It orbits the Sun at a distance of 0.7–3.2 AU once every 2 years and 8 months (975 days; semi-major axis of 1.92 AU). Its orbit has a high eccentricity of 0.64 and an inclination of 11° with respect to the ecliptic.[1] The body's observation arc begins with its official discovery observation at Socorro in September 1998.[2]

    Close approaches

    At about absolute magnitude 15.6, 1998 SS49 is one of the brightest and presumably largest known potentially hazardous asteroid (see PHA-list).[12] It has a very low Earth minimum orbital intersection distance of 0.0023 AU (340 thousand km; 0.90 LD).[1] On 26 November 1902, this asteroid made its closest near-Earth encounter since 1900 at a nominal distance of 0.0659 AU (9.86 million km; 25.6 LD). The next notable close approach will be on 21 November 2022 passing at a nominal distance of 0.141 AU (21,100,000 km; 13,100,000 mi).[1]

    1998 SS49 is also a Venus- and Mars-crosser, as it crosses the orbit of Venus and the Red Planet at c. 0.72 and 1.66 AU, respectively.

    Physical characteristics

    1998 SS49 is an assumed, stony S-type asteroid.[4]

    Rotation period

    In 2014, two rotational lightcurves of 1998 SS49 were obtained from photometric observations by American astronomer Brian Warner at the CS3–Palmer Divide Station in California (U82). Lightcurve analysis gave a rotation period of 5.370 and 5.66 hours and a brightness variation of 0.18 and 0.06 magnitude, respectively (U=2/2), one of which gave an alternative period solution of 2.686±0.002 hours.[8][10][lower-alpha 1][lower-alpha 2] In April 2016, the EURONEAR lightcurve survey measured a period of 5.398 hours with an amplitude of 0.12 magnitude (U=2).

    Diameter and albedo

    Surveys contrast: of the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer. These measure the object as between 2 and 3.484 kilometers lengthways (in diameter) and to have an albedo (optical wavelength reflectivity) between 0.076 and 0.237.[3][5][6][7] The Collaborative Asteroid Lightcurve Link assumes a stony typical albedo of 0.20 to calculate the diameter as 2.25 kilometers and an absolute magnitude of 15.6.[4]

    Numbering and naming

    This minor planet was numbered by the Minor Planet Center on 30 August 2004.[13] As of 2018, it has not been named.[2]

    Notes
    1. Lightcurve plot of (85713) 1998 SS49 – ambiguous rotation period 5.370±0.005 and 2.686±0.002 hours, by B. D. Warner at the CS3–Palmer Divide Station (2014). Quality code of 2. Summary figures at the LCDB and CS3 website.
    2. Lightcurve plot of (85713) 1998 SS49 – rotation period 5.66±0.01 hours, by B. D. Warner at the CS3–Palmer Divide Station (2014). Quality code of 2. Summary figures at the LCDB and CS3 website.

    References
    1. "JPL Small-Body Database Browser: 85713 (1998 SS49)" (2016-10-17 last obs.). Jet Propulsion Laboratory. Retrieved 18 January 2018.
    2. "85713 (1998 SS49)". Minor Planet Center. Retrieved 18 January 2018.
    3. Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117.
    4. "LCDB Data for (85713)". Asteroid Lightcurve Database (LCDB). Retrieved 18 January 2018.
    5. Nugent, C. R.; Mainzer, A.; Bauer, J.; Cutri, R. M.; Kramer, E. A.; Grav, T.; et al. (September 2016). "NEOWISE Reactivation Mission Year Two: Asteroid Diameters and Albedos". The Astronomical Journal. 152 (3): 12. arXiv:1606.08923. Bibcode:2016AJ....152...63N. doi:10.3847/0004-6256/152/3/63.
    6. Mainzer, A.; Grav, T.; Bauer, J.; Masiero, J.; McMillan, R. S.; Cutri, R. M.; et al. (December 2011). "NEOWISE Observations of Near-Earth Objects: Preliminary Results". The Astrophysical Journal. 743 (2): 17. arXiv:1109.6400. Bibcode:2011ApJ...743..156M. doi:10.1088/0004-637X/743/2/156.
    7. Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
    8. Warner, Brian D. (January 2015). "Near-Earth Asteroid Lightcurve Analysis at CS3-Palmer Divide Station: 2014 June-October". The Minor Planet Bulletin. 42 (1): 41–53. Bibcode:2015MPBu...42...41W. ISSN 1052-8091.
    9. Vaduvescu, O.; Macias, A. Aznar; Tudor, V.; Predatu, M.; Galád, A.; Gajdos, S.; et al. (August 2017). "The EURONEAR Lightcurve Survey of Near Earth Asteroids". Earth. 120 (2): 41–100. Bibcode:2017EM&P..120...41V. doi:10.1007/s11038-017-9506-9. hdl:10316/80202.
    10. Warner, Brian D. (April 2015). "Near-Earth Asteroid Lightcurve Analysis at CS3-Palmer Divide Station: 2014 October-December". The Minor Planet Bulletin. 42 (2): 115–127. Bibcode:2015MPBu...42..115W. ISSN 1052-8091.
    11. Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007.
    12. "List of the Potentially Hazardous Asteroids (PHAs)". Minor Planet Center. Retrieved 18 January 2018.
    13. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 24 February 2018.
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