(505657) 2014 SR339, provisional designation 2014 SR339, is a dark and elongated asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 970 meters (3,200 feet) in diameter. It was discovered on 30 September 2014, by NASA's Wide-field Infrared Survey Explorer telescope (WISE) in Earth's orbit.[1] Closely observed at Goldstone and Arecibo in February 2018, it has a rotation period of 8.7 hours.[5]
2014 SR339 is a member of the Apollo asteroids, which cross the orbit of Earth. Apollo's are the largest group of near-Earth objects with nearly 10 thousand known objects. It orbits the Sun at a distance of 0.90–1.70 AU once every 18 months (541 days; semi-major axis of 1.30 AU). Its orbit has an eccentricity of 0.30 and an inclination of 30° with respect to the ecliptic.[2] With an aphelion of 1.70 AU, it is also a Mars-crosser, as it crosses the orbit of the Red Planet at 1.666 AU. The body's observation arc begins with its official discovery observation by WISE in September 2014.[1]
As a potentially hazardous asteroid, 2014 SR339 has a minimum orbital intersection distance (MOID) with Earth of less than 0.05 AU and a diameter of greater than 150 meters. The Earth-MOID is currently 0.0354 AU (5,300,000 km), which translates into 13.8 lunar distances (LD).[2]
On 7 February 2018 it passed 0.054 AU (21 LD) from the Earth when its apparent magnitude brightened to 14.[3] Goldstone observed it until the following day.[6] While this was an 8.1-million kilometer flyby, the next close flyby of 6.3 million km will occur on 5 February 2058, and another 7.6 million km on 8 February 2095. It will also have a 3.2 million km flyby of Mars on 26 September 2048.[7]
The asteroid's spectral type is unknown. Due to its unusually low albedo (see below) it is likely a carbonaceous C-type asteroid.[2]
On 9 February, radiometric observations by the Arecibo Observatory revealed that the asteroid has an elongated, lumpy shape.[3] The radar images also gave it a rotational period between 8 and 9 hours.[5] A refined period of 8.7 hour agrees with (photometric) lightcurve observations by American photometrist Brian Warner at the Center for Solar System Studies (U82) during 9–11 February 2018, who obtained a period of 8.729 hours with a high brightness amplitude of 0.93 magnitude, which also indicates a non-spheroidal shape (U=3-).[3][a]
According to the survey carried out by the NEOWISE mission of NASA's WISE telescope, 2014 SR339 measures 0.971 kilometers in diameter and its surface has an albedo of 0.068.[4] During its close approach in February 2018, radiometric observations by Arecibo Observatory determined that the object is at least 1.5 kilometers (0.93 miles) wide.[3] Data from the Arecibo Telescope released in 2022 showed an unusually high radar albedo, possibly indicating rich metal content.[8]
This minor planet was numbered by the Minor Planet Center on 4 November 2017 (M.P.C. 107069).[9] As of 2018, it has not been named.[1]
Recent radar images of near-Earth asteroid (505657) 2014 SR339 from @NAICobservatory show a lumpy, elongated body at least 1.5 km long and rotating once every 8 to 9 hours!