Has NASA considered making a rover that can dig through the crust of Mars to find liquid water under the surface?
Let me clarify something. The “crust” is hugely thick on Mars. Like more than a Kilometer thick. We don’t have the capability to dig like that on Earth so we are way off from that kind of thing on Mars. But we have had landers that can Dig. The viking landers had arms that could dig, as will the Phoenix lander on 2007. We can dig a little with Spirit and Opportunity, but none of the digging is more than 10s of cms. Some people want to put a shovel on the Mars Science Laboratory, but that is to be determined.
