They've known since the original Viking Mission. The information was reserved to tell the sheeple at some point when they thought it suited them. Right now they need some funding for NASA so they've done up a press release about it.
Government is all about lying constantly about most anything all the time.
Notice that all the photos that amateurs have been telling us show clear evidence of life on Mars are now being acknowledged as same by NASA. So last year's tin foil helmet paranoid nut is this year's premier amateur scientist.
There's an easy acid test for all information from the televitz you can apply ...
If it's on televitz, itz a lie. Even when it isn't a lie, it's a way of lying by pretending to tell the truth. I hope that helps.