When 200,000 people applied for the Mars One project, a mission to colonize the red planet, they did so in the understanding that it would be a one-way trip. Whether they did so immediately or after years of scientific research, they were going to die on martian soil. At the time it was an obvious conclusion to draw. After all, nothing to have touched down on Mars has ever even tried to return to Earth.
That could all change. Since 2011, NASA has been considering SpaceX's Dragon capsule as a potential delivery vehicle for the space agency's next Mars rover in 2020. As it turns out, it might be able to do a bit more than that. A new study has proven that a modified Dragon capsule, dubbed "Red Dragon" could be capable of reaching Mars safely while also carrying a small rocket in its belly.
This second rocket could be loaded with soil samples and fired from the Red Dragon's belly. Returning to Earth orbit, the rocket would be greeted by a second Dragon capsule capable of safeguarding the samples through Earth's atmosphere. The idea is still just a proposal, and NASA doesn't plan to implement it until at least 2022 when the 2020 rover would have had ample time to gather some interesting samples.
As for the Mars One colonists, sadly the Earth-return capsule isn't big enough or equipped properly to carry a human being. That being said, if even a single rock can be brought back from the martian surface, maybe someday people will too. Of course they'll have to get there first.