We live in a village at the top of a very steep, mile deep, ice covered valley. Mercury is a village at the bottom of the valley. Your house is high up the va

We live in a village at the top of a very steep, mile deep, ice covered valley. Mercury is a village at the bottom of the valley. Your house is high up the valley but you actually live thirty feet deep in a pit. To get to Mercury you have to build a car, lift it out the pit, then slide down the steep valley. The car has to be lightweight so that you can lift it out the pit: the engine and brakes are weak and do next to nothing. So you build a feeble car — more of a four wheeled bicycle really, hoist it out the pit, and slide down the valley in it. By the time you whizz past Mercury you’re doing 100mph so you can’t stop. You go straight past and start sliding up the other side, but you do also put the brakes on for a bit. You’ll eventually slide back down to Mercury again at 90mph and put the brakes on again, and slow down a little more. Do this ~10x and you’ll eventually stop. Going in the other direction is easier. Earth is surrounded in a 100km soft squishy cushion of gas which means to all intents and purposes you can just fly straight at it.