This article needs to be updated. The reason given is: New Arecibo radar results presented at the 8th IAA Planetary Defense Conference in April 2023[1]. Please help update this article to reflect recent events or newly available information.(April 2023)
(52768) 1998 OR2 (provisional designation1998 OR2) is an asteroid on an eccentric orbit, classified as a near-Earth object and potentially hazardous asteroid of the Amor group, with a diameter of 2 kilometers (1.2 mi). It was discovered on 24 July 1998, by astronomers of the Near-Earth Asteroid Tracking (NEAT) program at the Haleakala Observatory, Hawaii, it passed very near to earth on 29 April 2020 at around 4:15am.[3] It is one of the brightest and therefore largest potentially hazardous asteroids known to exist.[7] With an observation arc of 35 years, the asteroid has a well-determined orbit, and its trajectory is well known through the year 2197.[2] The asteroid's orbit is only potentially hazardous on a time scale of thousands of years.[8]
Orbit and classification
Time lapse of asteroid 1998 OR2's motion in the sky on 9 April 2020
Orbit diagram of 1998 OR2
Arecibo radar images of 1998 OR2 taken over a two-hour period in April 2020
Animation of 1998 OR2 close approach in 2020
1998 OR2 is a member of the dynamical Amor group of near-Earth asteroids,[2][3] and therefore does not currently cross Earth's orbit. The asteroid's closest approach to the Sun is just outside Earth's farthest distance from the Sun. When the asteroid has a perihelion point less than 1.017 AU (Earth's aphelion), it is classified an Apollo asteroid. This asteroid's category flips back and forth as time passes, due to minor perturbations of its orbit.
It orbits the Sun at a distance of 1.0–3.7 AU once every 3 years and 8 months (1,344 days; semi-major axis of 2.38 AU). Its orbit has a high eccentricity of 0.57 and an inclination of 6° with respect to the ecliptic. With its sufficiently large aphelion, this asteroid is also classified as a Mars-crosser, crossing the orbit of Mars at 1.66 AU.[2]
With an absolute magnitude of approximately 15.8,[3]1998 OR2 is one of the brightest and presumably largest-known potentially hazardous asteroids (see PHA-list).[7] It currently has an Earth minimum orbital intersection distance of 0.0087 AU (1,300,000 km), which translates into 3.4 lunar distances (LD).[2] On 16 April 2079, this asteroid will make a near-Earth encounter at a safe distance of 0.0118 AU (4.59 LD), and pass the Moon at 0.0092 AU (3.6 LD).[2] The asteroid's orbit is only potentially hazardous on a time scale of hundreds, if not thousands, of years.
On 29 April 2020 at 09:56 UTC, the asteroid passed at a distance of 0.042 AU (6.3 million km; 16 LD) from Earth.[2] With observations as recent as April 2020 and a 32-year observation arc, the 2020 close approach distance was known with an accuracy of roughly ±6 km.[9] (For comparison, Venus will be 0.29 AU or 43 million km or 110 LD from Earth on 3 June 2020.)
History of close approaches of large near-Earth objects since 1908 (A)
(A) List includes near-Earth approaches of less than 5 lunar distances (LD) of objects with H brighter than 18. (B)Nominal geocentric distance from the Earth's center to the object's center (Earth radius≈0.017 LD). (C) Diameter: estimated, theoretical mean-diameter based on H and albedo range between X and Y. (D) Reference: data source from the JPL SBDB, with AU converted into LD (1 AU≈390 LD) (E) Color codes: unobserved at close approach observed during close approach upcoming approaches
Physical characteristics
Animation of radar images showing 1998 OR2's rotation
According to observations by the NASA IRTF telescope during the ExploreNEOs Warm Spitzer program, 1998 OR2 is a rather rare L-type asteroid.[10] Delay-Doppler radar observations by the Arecibo Observatory in April 2020 have shown that 1998 OR2 bears a large, crater-like concavity in its shape.[11] These radar observations have also resolved several other topographic features on the asteroid's surface, such as hills and ridges.[12]
Rotation period
In 2009, rotational lightcurves of 1998 OR2 were obtained from photometric observations by astronomers in Salvador, Brazil, and during the Lowell Observatory Near-Earth Asteroid Photometric Survey (NEAPS). Lightcurve analysis gave a rotation period of 3.198 and 4.112 hours with a brightness amplitude of 0.29 and 0.16 magnitude, respectively (U=2/2+).[13][14] The latter rotation period of 4.1 hours was later confirmed by radar observations of the asteroid in 2020.[12][11]
Diameter and albedo
The Collaborative Asteroid Lightcurve Link (CALL) assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 2.15 km (1.34 mi) based on an absolute magnitude of 15.7.[15] It is the first near-earth asteroid to show evidence of shock darkening: the slow darkening of the surface over time, from micrometeorites and solar wind.[5]
^1998 OR2's rotational north pole direction is given in terms of ecliptic coordinates, where λ is ecliptic longitude and β is ecliptic latitude.[1]: 6 β is the angular offset from the ecliptic plane, whereas inclinationi with respect to the ecliptic is the angular offset of the asteroid's rotational north pole from the ecliptic north pole at β = +90° ;i with respect to the ecliptic would be the complement of β.[4] Therefore, given β = +20.7° ,i = 90° – (+20.7°) = 69.3° from the ecliptic.
^"Coordinate transformations". Astronomy and Astrophysics. European Southern Observatory. January 1998. Archived from the original on 17 June 2021. Retrieved 5 April 2023.
^Betzler, Alberto Silva; Novaes, Alberto Brum (October 2009). "Photometric Observations of 1998 OR2, 1999 AQ10, and 2008 TC3". The Minor Planet Bulletin. 36 (4): 145–147. Bibcode:2009MPBu...36..145B. ISSN1052-8091.
^Koehn, Bruce W.; Bowell, Edward G.; Skiff, Brian A.; Sanborn, Jason J.; McLelland, Kyle P.; Pravec, Petr; et al. (October 2014). "Lowell Observatory Near-Earth Asteroid Photometric Survey (NEAPS) - 2009 January through 2009 June". The Minor Planet Bulletin. 41 (4): 286–300. Bibcode:2014MPBu...41..286K. ISSN1052-8091.
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