The asteroid was first identified as 1938 WL at the Finnish Turku Observatory in November 1938, extending the body's observation arc by 35 years prior to its official discovery observation at Nauchnij.
In March 2013, two rotational lightcurves of Lexell were obtained from photometric observations by Gary Haagen at Stonegate Observatory, Massachusetts, and by a group of astronomers at the Oakley Southern Sky Observatory (E09), Australia. Lightcurve analysis gave a well-defined rotation period of 5.441 and 5.4429 hours with a brightness variation of 0.45 and 0.42 magnitude, respectively (U=3/3).
In February 2013, observations made by French amateur astronomer Pierre Antonini gave a concurring period of 5.44 hours with an amplitude of 0.51 magnitude (U=3-).
Diameter and albedo
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Lexell measures 7.255 and 7.456 kilometers in diameter and its surface has an albedo of 0.306 and 0.2908, respectively. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 – derived from 8 Flora, the largest member and namesake of the Flora family – and calculates a diameter of 7.82 kilometers based on an absolute magnitude of 12.7.