M-type asteroid
Although "Hertha" has long been classified as an M-type asteroid based on its spectral properties, observations carried out by Rivkin "et al." in 1996 using the IRTF at Mauna Kea Observatory have raised the possibility of reclassification. The presence of a dip in the observed spectrum at 3 μm indicates that the surface is hydrated, suggesting that "Hertha" should be reclassified as a W-type (a "wet M-type") asteroid. Based on work carried out by Salisbury and Walter, the Rivkin study estimated the water content of the asteroid to be between 0.14 and 0.27 percent by mass. This estimate is based on laboratory measurements and may not be applicable to asteroids in space.