The Fifth Man, by John B. Olson, Randall Scott Ingermanson
This is such an excellent book - I'm guessing it is volume 2 of 3, now that we've had "Oxygen" about getting to Mars, this book about being on Mars.... hmm, what is next? Ah, going home, of course.
This is a solid, hard science story about what it might be like to be on Mars. What would be the consequences of discovering life? What are the psycho-dynamics of a mission of four people over a period of YEARS. National and international politics. And a very realistic portrayal (in this book and the last) about NASA problem solving in Apollo 13-type situations. Oh and there is romance - and moral issues of good and evil.
The real shame is that this book is pretty much consigned to the "Christian fiction" ghetto, when it should be up there scrapping for a Hugo or Nebula. I wish Bethany would cut a deal with TOR or DAW and get these books in the open market!