(162421) 2000 ET70

(162421) 2000 ET70 is a dark, elongated and oblate asteroid, classified as near-Earth object and potentially hazardous asteroid of the Aten group, approximately 2.2 kilometers in diameter. It was discovered on 8 March 2000, by astronomers of the Lincoln Near-Earth Asteroid Research at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico.[2] The body has a notably low albedo, and its shape resembles that of a "clenched fist".[3][4]

(162421) 2000 ET70
Discovery [1][2]
Discovered byLINEAR
Discovery siteLincoln Lab's ETS
Discovery date8 March 2000
Designations
(162421) 2000 ET70
2000 ET70
NEO · PHA · Aten [1][2]
Orbital characteristics [1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc37.17 yr (13,575 d)
Aphelion1.0638 AU
Perihelion0.8295 AU
0.9467 AU
Eccentricity0.1237
0.92 yr (336 days)
129.36°
1° 4m 12.36s / day
Inclination22.323°
331.16°
46.103°
Earth MOID0.0316 AU · 12.3 LD
Physical characteristics
Dimensions2.6 × 2.2 × 2.1 km[3]
2.9 × 2.2 × 1.5 km[4]
2.0±0.2 km[5]
2.10±0.07 km[4]
2.26±0.11 km[3][6]
8.94±0.04 h[5]
8.9444±0.0008 h[4]
8.947±0.001 h[7][lower-alpha 1]
8.96±0.01 h[3]
0.018±0.002[3][6]
0.065±0.05[4]
Xk [4]
18.0[1] · 18.2[3][6]

    Orbit and classification

    2000 ET70 orbits the Sun at a distance of 0.8–1.1 AU once every 11 months (336 days; semi-major axis of 0.95 AU). Its orbit has an eccentricity of 0.12 and an inclination of 22° with respect to the ecliptic.[1] A first precovery was found in the Digitized Sky Survey from images taken at ESO's La Silla Observatory in February 1977. The body's observation arc begins with its official discovery observation at Socorro in March 2000.[2]

    Close approaches

    The asteroid has an Earth minimum orbital intersection distance of 0.0316 AU (4,730,000 km) which translates into 12.3 lunar distances.[1] In February 2012, it was observed by radar during a close approach (0.045 AU) at the Arecibo and Goldstone observatories. The observations allowed to model the body's spin period and rotation, as well as its shape (see below).

    Physical characteristics

    2000 ET70 has been characterized as a Xk-subtype, which transitions between the X- and K-type asteroids.[4]

    Rotation period, pole, and shape

    During its close approach in February 2012, a rotational lightcurve of 2000 ET70 was obtained from photometric observations by a collaboration of astronomers from Uruguay, Australia, and the United States. Analysis of the lightcurve gave a period of 8.947 hours with a brightness amplitude of 0.60 magnitude (U=3-).[7][lower-alpha 1]

    Radar observations at Arecibo and Goldstone showed that the asteroid spins in a retrograde manner with a rotation period of 8.96 hours. It is likely a principal axis rotator, i.e., not tumbling.[3] Shape modelling by two independent teams gave sidereal periods of 8.96 and 8.944 hours, respectively.[3][4] A spin axis of (80.0°, −50.0°) in ecliptic coordinates was determined.[3] The observations also revealed that the asteroid has an elongated oblate shape, resembling a "clenched fist". Its surface exhibits multiple kilometer scale ridges and concavities.[3][5]

    Diameter and albedo

    According to shape modeling of radar observations, the asteroid's overall dimensions are 2.6 × 2.2 × 2.1 kilometers.[3] Based on an absolute magnitude of 18.2, this results in a notably low albedo of 0.018.[3] More recent modeling combining radar, photometric, and infrared data gave and even more elongated shape of 2.9 × 2.2 × 1.5 kilometers.[4] These authors argue that the absolute magnitude value is incorrect and report a geometric albedo of 0.09.[4]

    2000 ET70's mean-diameter measures between 2.0 and 2.26 kilometers and its surface has an albedo between 0.018 and 0.09.[3][4] The Collaborative Asteroid Lightcurve Link adopts an albedo of 0.018 and a diameter of 2.26 kilometers based on an absolute magnitude of 18.2.[3][6]

    Numbering and naming

    This minor planet was numbered on 26 September 2007, after its orbital parameters had been sufficiently determined (M.P.C. 60670).[8] As of 2018, it has not been named.[2]

    Notes
    1. Lightcurve plot of (162421) 2000 ET70, by Julian Oey (2012) at Blue Mountains Observatory (Kingsgrove Observatory; E19). Lightcurve period 8.970±0.004 hours. Note: additional photometric data from other observatories gave a refined period of 8.947 hours.[lower-alpha 2] Summary figures at the LCDB

    References
    1. "JPL Small-Body Database Browser: 162421 (2000 ET70)" (2014-04-20 last obs.). Jet Propulsion Laboratory. Retrieved 28 November 2017.
    2. "162421 (2000 ET70)". Minor Planet Center. Retrieved 28 November 2017.
    3. Naidu, Shantanu P.; Margot, Jean-Luc; Busch, Michael W.; Taylor, Patrick A.; Nolan, Michael C.; Brozovic, Marina; et al. (September 2013). "Radar imaging and physical characterization of near-Earth Asteroid (162421) 2000 ET70". Icarus. 226 (1): 323–335. arXiv:1301.6655. Bibcode:2013Icar..226..323N. doi:10.1016/j.icarus.2013.05.025.
    4. Marshall, Sean E.; Howell, Ellen S.; Magri, Christopher; Vervack, Ronald J.; Campbell, Donald B.; Fernández, Yanga R.; et al. (August 2017). "Thermal properties and an improved shape model for near-Earth asteroid (162421) 2000 ET70". Icarus. 292: 22–35. arXiv:1610.04653. Bibcode:2017Icar..292...22M. doi:10.1016/j.icarus.2017.03.028.
    5. Naidu, Shantanu; Margot, J. L.; Taylor, P. A.; Nolan, M. C.; Brozovic, M.; Benner, L. A. M.; et al. (October 2012). "Radar Observations and Shape Modeling of Near-Earth Asteroid (162421) 2000 ET70". American Astronomical Society: 302.06. Bibcode:2012DPS....4430206N.
    6. "LCDB Data for (162421)". Asteroid Lightcurve Database (LCDB). Retrieved 28 November 2017.
    7. Alvarez, Eduardo Manuel; Oey, Julian; Han, Xianming L.; Heffner, Orry R.; Kidd, Adam W.; Magnetta, Bradley J.; et al. (July 2012). "Period Determination for NEA (162421) 2000 ET70". The Minor Planet Bulletin. 39 (3): 170. Bibcode:2012MPBu...39..170A. ISSN 1052-8091.
    8. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 28 November 2017.
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