Miss Dada  🏳️‍⚧️

I'm not going to go into detail about the Oberth effect, but this particular case is easy to think about. Your spaceship's engine makes you go faster or slower the same amount no matter what. If you're in a *really* high orbit, you're going very slowly

You can think about it like throwing a ball high up, almost straight up but not quite. That's basically what your orbit looks like right before you escape the solar system. So at the highest point, you're going only a few hundred meters per second.

Which means that completely stopping is trivial. And if you're not moving, you're not in orbit. So you will fall straight down (what goes up must come down after all. The only difference is now you're not moving fast enough to miss the ground).

So if you answered "orbit of mercury" thinking about this exact maneuver, you were right. But it's not how I meant the question. The point of all of this is that most folks don't realize just how fast we are moving around the sun right now.

You are currently moving at nearly 30 km/s around the sun. That is so fast that you need to go barely 25% faster to leave the solar system and never come back. Cancelling that velocity is *really* hard.

Now that's not to say that reaching Mercury isn't hard. It is. Mercury is going even faster than we are (nearly 50 km/s relative to the sun!) Only one satellite in history has orbited Mercury, which was MESSENGER in 2004. It needed 4 gravity assists to do so (1 earth 3 venus)

I phrased the question as "requires the least energy" specifically to avoid clever gravity assists. In theory, you can reach all three destinations just by getting to the moon. Enough gravity assists there gets you to solar orbit, earth to venus, venus to jupiter, etc.

But that phrasing was nonsense because so much of this is kinetic vs potential energy, which doesn't really work with that phrasing. A lot of folks asked "orbiting mercury or reaching a similar orbit of Mercury?" As I phrased it it actually doesn't matter.