158999

158999 is a numbered minor planet of the asteroid belt assigned the provisional designation 2002 XY21. It was discovered on 14 October 2002 by the Sloan Digital Sky Survey in the near‑east horizon region of the sky. Observations were made at the Apache Point Observatory using the 2.5‑meter telescope with the SDSS camera.

The orbit of 158999 has a semi‑major axis of 2.74 AU, a perihelion of 2.35 AU and an aphelion of 3.13 AU. Its orbital eccentricity is 0.14 and the inclination relative to the ecliptic plane is 12.7°. The asteroid completes an orbit around the Sun approximately every 4.50 years (1642 days). The objects in this orbital group are considered typical Main Belt asteroids, with no obvious resonance with Jupiter or other planets.

Preliminary spectrophotometric analysis indicates that 158999 is of the S–type, meaning it is composed primarily of silicate rock and nickel‑iron metal. Its absolute magnitude is 13.7, giving an estimated diameter of about 4.6 km assuming a typical albedo of 0.20. The rotation period of the asteroid has not yet been measured by photometric light‑curve studies, and it remains an object of interest for future rotational and radar investigations.

Currently, 158999 is cataloged in the Jet Propulsion Laboratory (JPL) Small‑Body Database and in the Minor Planet Center database. No spacecraft missions are planned to visit this asteroid and it has not been named beyond its numerical designation.

---