The Spectral Properties of Pitted Impact Melt Deposits on Mars

Abstract

The ‘pitted impact deposits’ on Mars (e.g., Fig. 1) are clustered, polygonally-shaped devolatilization pits that occur ubiquitously on the Martian surface within primary ejecta deposits of impact craters. They were thoroughly studied by [1] and [2], providing details about their geographical distribution, geological appearance and formation mechanism. They occur preferentially in mid-latitudes, which emphasizes the significance of the prevailing volatile/rock-ratio. Moreover, their preservation states and sizes correlate positively with preservation states and sizes of their host craters, showing that they can also be obscured over geological times scales. The pits form by rapidly escaping steam and it was estimated [2] that this process takes place within a few weeks or even months, depending on the abundance of volatiles and deposit thickness. It was also suggested that clasts/particles of diverse sizes were entrained within the escaping steam, thus being transported from the interior deposit to the surface. The ejecta material was concluded to most likely resemble a melt-bearing breccia, showing similarities to the suevite of the Ries crater in Germany [1,3].

Pitted impact deposits also occur on the main belt asteroid Vesta [4], partly exhibiting distinct spectral properties like higher overall reflectance, higher pyroxene absorption strength and a depletion in hydroxyl with respect to their immediate surrounding [5]. The scope of this study is therefore to characterize the spectral properties of the pitted impact deposits on Mars in general, as well as to determine whether the Martian pits exhibit similar distinct spectral properties as observed on Vesta.