Pete Theisinger, manager of the Mars Exploration Rover project, says Spirit is in "critical condition" as it sits at Gusev Crater.
"We do not know to what extent we can restore functionality to the system because we don't know what's broke. We don't know what started this chain of events. I think, personally, that is a sequence of things. And we don't know, therefore, the consequences of that.
"I think it is difficult, at this very preliminary stage, to assume that we did not have some type of hardware event that caused this to start. Therefore, we don't know to what extent we can work around that hardware event and to what extent we can get the software to ignore that hardware event, if that is what we eventually have to do.
"So we have a long way to go here with the patient in 'intensive care.' But we have been able to establish that we can command it, and we have been able to establish that it can give us information, and we have been able to establish that the power system is good and we are thermally OK. Those are all very, very, very important pieces of information and state.
"We are a long, long, long way from being done here. But we do have serious problems and our ability to eventually work around them is unknown.
"I'm trying to tell you do not to expect a big sea change in either knowledge or theory in the next several days because this is a very complex problem and we have very limited visibility."
"We made good progress overnight and the rover has been upgraded from critical to serious. We have a working hypothesis we are pursuing that is consistent with many of the observables and consistent with operations that we performed on the vehicle last night. It involves the flash memory on the vehicle and the software used to communicate with that memory.