Slowing for Mars

Over the summer, NASA and JPL tested hardware that they're hoping will give humanity far better access to Mars. That's a hard trip. Mars isn't exactly next door -- well, on a solar system scale, it is, but it's still a six month journey of hundreds of million of kilometers -- so the technical problems just with getting there are legion. If you overcome them, you still have a payload moving at multiple kilometers per second relative to the planet. How do you slow it down for a soft landing? If y...