What we expect to find, certainly in our own solar system, are probably simple single or multiple-cell forms of life. To get to intelligent life takes stability of conditions over huge, long periods of time.

Humans can actually read a landscape, go through a lot of rocks - crack them open, throw them, pick up the next one. Rovers are great - they do amazing science - but it is a lot more tedious process; they go much less far than a human can cover in a day.

I always like to say just think you were a doctor with only one patient. You might understand how that person gets sick, how they get better, but you understand nothing about the progression of disease or how humans in general get ill. Now take an Earth scientist: you only have one planet to study.

Ellen Stofan Quotes