789 Lena

789 Lena, provisional designation , is a metallic asteroid from the middle region of the asteroid belt, approximately 24 kilometers in diameter. It was discovered on 24 June 1914, by Soviet–Russian astronomer Grigory Neujmin at Simeiz Observatory on the Crimean peninsula, and named after the discoverer's mother.

Orbit and classification
Lena orbits the Sun in the middle main-belt at a distance of 2.3–3.1 AU once every 4 years and 5 months (1,608 days). Its orbit has an eccentricity of 0.15 and an inclination of 11° with respect to the ecliptic. Lena's observation arc begins with its first used observation made at Yerkes Observatory in 1935, or 21 years after its official discovery observation at Simeiz.

Although its orbital elements resemble those of the asteroids in the Eunomia family, true members of this family have a S-type composition, so it is almost certainly an unrelated interloper.

Physical characteristics
In the SMASS taxonomy, Lena is an X-type asteroid. It has also been characterized as a metallic M-type asteroid by NASA's Wide-field Infrared Survey Explorer (WISE).

Rotation period
In 1993, a rotational lightcurve which was later proven incorrect, was obtained from photometric observations at the Félix Aguilar Observatory, Argentina. It gave an unusual lightcurve, indicating a very irregular shape and/or a relatively long rotation period of 22 hours with an exceptionally high amplitude of 1.5 in magnitude (U=0).

In August and September 2007, two reliable lightcurves were obtained by Italian astronomer Silvano Casulli and by members at the U.S.Oakley Observatory. Lightcurve analysis gave a period of $20.56$ and $22.483$ hours, with a brightness variation of 0.50 and of 0.40 magnitude, respectively (U=3/2+).

Diameter and albedo
According to the space-based surveys carried out by the Japanese Akari satellite and the NEOWISE mission of the WISE telescope, Lena measures between 20.6 and 23.9 kilometers in diameter, and its surface has an albedo of 0.137–0.186. The Collaborative Asteroid Lightcurve Link assumes a much lower albedo of 0.10 and calculates a diameter of 24.2 kilometer, as the lower the albedo (reflectivity), the larger a body's diameter, at a constant absolute magnitude (brightness).

Naming
This minor planet was named in honor of Elena ("Lena") Petrovna Neujmina (1860–1942), mother of the discovering astronomer Grigory Neujmin.