olation . ▁S cal loped ▁de press ions ▁are ▁believed ▁to ▁form ▁from ▁the ▁removal ▁of ▁sub sur face ▁material , ▁possibly ▁inter st it ial ▁ice , ▁by ▁sub lim ation . ▁This ▁process ▁may ▁still ▁be ▁happening ▁at ▁present . ▁ ▁On ▁November ▁ 2 2 , ▁ 2 0 1 6 , ▁NASA ▁reported ▁finding ▁a ▁large ▁amount ▁of ▁under ground ▁ice ▁in ▁the ▁U top ia ▁Plan it ia ▁region ▁of ▁Mars . ▁The ▁volume ▁of ▁water ▁detected ▁has ▁been ▁estimated ▁to ▁be ▁equivalent ▁to ▁the ▁volume ▁of ▁water ▁in ▁Lake ▁Super ior . ▁The ▁volume ▁of ▁water ▁ice ▁in ▁the ▁region ▁were ▁based ▁on ▁measurements ▁from ▁the ▁ground - pen etr ating ▁rad ar ▁instrument ▁on ▁Mars ▁Re con na issance ▁Or b iter , ▁called ▁SH AR AD . ▁ ▁From ▁the ▁data ▁obtained ▁from ▁SH AR AD , ▁" die lect ric ▁perm itt ivity ", ▁or ▁the ▁die lect ric ▁constant ▁was ▁determined . ▁The ▁die lect ric ▁constant ▁value ▁was ▁consistent ▁with ▁a ▁large ▁concentration ▁of ▁water ▁ice . ▁ ▁, ▁ ▁Ped est al ▁C rat ers ▁A ▁ped est al ▁cr ater ▁is ▁a ▁cr ater ▁with ▁its ▁e ject a ▁sitting ▁above ▁the ▁surrounding ▁terrain ▁and ▁thereby ▁forming ▁a ▁raised ▁platform ▁( like ▁a ▁ped est al ). ▁They ▁form ▁when ▁an ▁impact ▁cr ater ▁e ject s ▁material ▁which ▁forms ▁an ▁er os ion - res istant ▁layer , ▁thus ▁causing ▁the ▁immediate ▁area ▁to ▁er ode ▁more ▁slowly ▁than