>>11437354He's completely wrong actually, Mercury is on par with the Outer planets in total delta v costs.
Humans tend to think of the Sun as "down" and Mars/Outer solar system as "up," because we live in an environment where down and up are very important. But space is 4 dimensional, there is no "up" or "down" in space, direction is completely relative to a reference object. It actually costs more delta v to go into a lower orbit than a higher orbit, because the gravity of the Sun increases the inertia of an object as it gets closer. This is why the planets have largely migrated outward and not inward as the Solar system aged.
It would takes nearly as much delta v to get close to the Sun as it takes to escape the Suns influence, which is why solar probes are some of the fastest moving objects made by Man. The faster something is moving, the more energy it takes to change its movement.
