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]

Close approaches edit

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]

2018 flyby edit

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]

Rotation period edit

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]

Diameter and albedo edit

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]

•  
  Daily motion of asteroid across sky
•  
  View of flyby above the earth and moon

• List of the Potentially Hazardous Asteroids (PHAs), Minor Planet Center
• List Of Apollo Minor Planets (by designation), Minor Planet
• Asteroid Lightcurve Database (LCDB), query form (info Archived 16 December 2017 at the Wayback Machine)
• (505657) 2014 SR339 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• (505657) 2014 SR339 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• (505657) 2014 SR339 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters