Shooting a rocket from Mars

Returning a sample of Martian soil has been seriously discussed at least since the Viking landers in the 70s.  But there's no really simple way to solve it.  Landing a rocket on Mars big enough to take a sample directly back to Earth means shipping a lot of mass to Mars, which by one estmate costs a good $1M per kilogram. Doing it any other way means a rendezvous in Martian orbit.  That's where NASA is headed now: the Mars 2020 rover will collect and study samples and take them to a surface point where another spacecraft (not yet built) with a rocket will land, and then the rocket lofts the samples or dock with an orbiter and send them to Earth.  (It's almost enough to make you think it's easier to just send astronauts, although that option still seems far off at out current rate of progress.)   There are a host of challenges here, and this article is a good introduction. (image NASA)