This article is very light on details, so if you actually want to read about the problems, and the great work NASA and DLR scientists are doing to rescue the mission, have a look here:
https://www.dlr.de/blogs/en/desktopdefault.aspx/tabid-5893/9577_read-1090/
Basically, the soil in this location is an extremely fine soft powder, which has formed a hole around the mole. The Mole requires friciton on it's side walls to operate, so sitting in a hole means it cant grib and cant penetrate beyond the 20 or so cm it already has. There are ways to dig into such soil (as similar soils do exist here on earth) and the team will be pushing forward with those.
There is still a possibility that the mole has encountered a second rock under the surface (it encountered one in the first 10cm but was able to deflect past it), but the more likely problem is this super fine soil. Once through this top layer, the Mole should be able to operate without problems. Of course that's a big "should", as it's impossible to know how deep the fine soil goes, and what lays beneath. Still now that the Mole is free from its support structure, and engineers can see directly what the mole is doing when it tries to penetrate, chances of a successful mission are greatly increased.
Good work by the whole team, and good luck for getting the mole down deep! (from an ex-HP3 team member)... :)
Biting the hand that feeds IT
