system
Given the following post, respond as if you're commenting on Reddit:
human
If Venus is hotter than Mercury why haven’t we explored Mercury more?

If my research is correct it looks like we’ve only sent two probes to come close to Mercury and no landings. But we’ve landed on Venus. What’s stopping us from going to Mercury?
gpt
Mercury is harder to get to and harder to land on.

Slowing down isn't "free" in space. It takes as much energy to slow down as it does to speed up. The Earth is already orbiting the Sun at 30 km/s, so if you want to fall inwards to explore the inner solar system, you have to get rid of most of that speed. To escape the solar system you need to be going at 42 km/s, so you only need an extra 12 km/s. But to drop all the way down to the Sun, you'd need to drop basically the full 30 km/s. So moving inwards can be more expensive than moving outwards - and the further inwards you go, the more energy you need. Getting to Venus means you need to shed about 10 km/s of speed. Getting to Mercury means you need to drop by about 14 km/s. So it takes less thrust to get to Pluto than to get to Mercury (even if getting to Mercury is faster!)

This also means that braking to land on a planet isn't free either. Venus's thick atmosphere is actually useful here - because aerobraking actually is almost "free". You may need a heat shield, but that's usually much less weight and cost than using rockets. And after braking in the upper atmosphere, you can just use parachutes to float down to the surface. Even the thin atmosphere of Mars is useful here - parachutes might not be enough for a heavy rover to land safely, but you can at least get rid of a lot of your momentum with aerobraking and parachutes, and only use a little rocket-powered lander at the end. But on Mercury, there's no free lunch. You have to pack enough rockets to completely stop your motion relative to the planet, and then land yourself safely, and it all has to be fully computer-controlled because the time delay is too long for remote control. Note that all of the solar system bodies we have landed on have either had atmospheres, or are asteroids or comets with almost no gravity (so it's more of a rendezvous than a landing), with the sole exception of the Moon, which is bar far the closest large object to Earth.

So even though a lander might survive for longer on Mercury than on Venus, it generally takes more energy to get to the inner solar system than the outer solar system, and it takes more energy (and more precision!) to land on a planet or moon with no atmosphere than on one where you can aerobrake and use a parachute. This adds up to make Mercury one of the most difficult places to land in the solar system.