[en] | (52768) 1998 OR2

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]

The body’s observation arc begins with a precovery published by the Digitized Sky Survey taken at the Siding Spring Observatory in June 1986, more than 12 years prior to its official discovery observation at Haleakala Observatory, Hawaii.^[3]

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.)

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]

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]

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]

• Asteroid Lightcurve Database (LCDB), query form (info Archived 16 December 2017 at the Wayback Machine)
• Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend
• (52768) 1998 OR2 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• (52768) 1998 OR2 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• (52768) 1998 OR2 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters