221516

221516 is a minor planet located in the main asteroid belt between Mars and Jupiter. It received its provisional designation 2003 GD and was discovered on 10 March 2003 by the Catalina Sky Survey at Mount Lemmon Observatory in Arizona, United States. The discoverers were not credited with a personal naming, so the asteroid retains its numerical designation rather than a formal name.

The orbit of 221516 is moderately eccentric, with an eccentricity of approximately 0.21. It has a semimajor axis near 2.4 astronomical units, placing it squarely within the central zone of the main belt. The orbital period is about 3.7 Earth years, or roughly 1,350 days. The inclination relative to the ecliptic plane is about 6 degrees, indicating that the asteroid's orbit is neither highly tilted nor highly aligned with the plane of the solar system.

Observational data suggest that 221516 is a relatively small object, with an estimated diameter of about 4 to 5 kilometers, based on absolute magnitude calculations and assumed albedo values typical for S‑type asteroids. The composition has not been directly measured, but its spectral classification is presumed to be similar to other asteroids in its orbital region.

No spacecraft missions have visited 221516, and it has not been observed for significant activity such as outgassing. Its rotation period and shape remain unknown due to limited photometric studies. Future observing campaigns may provide more precise measurements of its physical properties and confirm its classification.