Im not a scientist....but everyone knows that there is currently no life on Mars and probably never was life on Mars....Does anyone at NASA believe there is a covered civilization beneath thr Mars landscape?
I do not think anyone believes they will find little green men or underground civilizations.
Where there is water there is a chance of life, microbes, single cell creatures. Those have been found in the most hostile to life places on earth so there is no doubt if they find water there will be some sort of life.