Hm, I am totally unsure of how this fits into the whole framework of the story. While definitely interesting (memory manipulation is a very intriguing premise for an experiment and whatnot), I'm not sure why this is part of their communication...
Nonetheless, it very well COULD be, if some substantial background info was given on the situation.
First things first: it's a fabulous premise. Correspondences are so great; you learn a lot about the characters through them.
Nice atmosphere you have set up on Mars. The description is well put, but I'm slightly irked by the writer's indecision over actually liking the place or not, That's personal though, and doesn't detract from the flow or style. The idea of the sterilization process is great too; that one line conveys everything about it.