3   μ m ▁indicates ▁that ▁the ▁surface ▁is ▁hyd r ated , ▁suggesting ▁that ▁Her tha ▁should ▁be ▁rec lass ified ▁as ▁a ▁W - type ▁( a ▁" w et ▁M - type ") ▁astero id . ▁ ▁Based ▁on ▁work ▁carried ▁out ▁by ▁Sal is bury ▁and ▁Walter , ▁the ▁Riv kin ▁study ▁estimated ▁the ▁water ▁content ▁of ▁the ▁astero id ▁to ▁be ▁between ▁ 0 . 1 4 ▁and ▁ 0 . 2 7 ▁percent ▁by ▁mass . ▁This ▁estimate ▁is ▁based ▁on ▁labor atory ▁measurements ▁and ▁may ▁not ▁be ▁applicable ▁to ▁astero ids ▁in ▁space . ▁ ▁A ▁more ▁recent ▁study ▁by ▁Riv kin ▁et ▁al . ▁published ▁in ▁ 2 0 0 2 ▁exam ined ▁the ▁dependence ▁of ▁spectral ▁absor ption ▁on ▁the ▁astero id ' s ▁rot ational ▁phase . ▁ ▁The ▁study ▁looked ▁at ▁the ▁ 0 . 7   μ m ▁band , ▁which ▁is ▁also ▁associated ▁with ▁hyd r ated ▁sil ic ates , ▁and ▁found ▁that ▁the ▁reflect ance ▁changes ▁as ▁the ▁astero id ▁rot ates , ▁suggesting ▁that ▁the ▁surface ▁is ▁heter ogeneous ▁with ▁some ▁hyd r ated ▁areas ▁inter m ixed ▁with ▁dry ▁areas . ▁ ▁Ast ero id ▁family ▁ ▁Her tha ▁is ▁one ▁of ▁the ▁core ▁members ▁of ▁the ▁N ys a ▁family ▁( 4 0 5 ) ▁also ▁known ▁as ▁H erta ▁family . ▁The ▁N ys a – Pol ana ▁complex ▁is ▁the ▁main - b elt ' s ▁largest ▁grouping ▁of ▁astero ids ▁with ▁nearly