It was discovered on 5 October 1929, by American astronomer Clyde Tombaugh at Lowell Observatory during his search for Pluto.

[9] The presumed S-type asteroid has a rotation period of 10.5 hours and measures approximately 5 kilometers (3.1 miles) in diameter.

[10] The first rotational lightcurve of Annette was obtained by American astronomer Brian Warner at his Palmer Divide Observatory, Colorado, in December 2005.

[7] In November 2006, a second lightcurve by astronomer Robert Buchheim at Altimira Observatory in southern California gave a concurring period of 10.4595 hours and an amplitude of 0.64 magnitude (U=3).

[8] According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Annette measures between 5.41 and 7.562 kilometers in diameter and its surface has an albedo between 0.056 and 0.47,[4][5][6] while the Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 – derived from 8 Flora, the largest member and namesake of its family – and calculates a diameter of 3.66 kilometers using Robert Buchheim's fainter absolute magnitude of 14.35.