[16] In October 2005, a rotational lightcurve of Erna was obtained from photometric observations by French and Italian astronomers Raymond Poncy (177), Roberto Crippa (A12), Federico Manzini and Silvano Casulli.

[12] Another lightcurve from the Palomar Transient Factory in November 2010 gave a similar period of 8.790 hours with an amplitude of 0.35 magnitude (U=2).

[13] In 2013, an international study modeled a lightcurve from various data sources including the Uppsala Asteroid Photometric Catalogue and the Palomar Transient Factory survey.

The modeling gave a concurring period of 8.79079 hours and determined two spin axis in ecliptic coordinates (λ, β) of: (357.0°, −49.0°) and (161.0°, −60.0°).

[7][8][9][10][11][15] The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0524 and a diameter of 49.19 kilometers based on an absolute magnitude of 10.36.