Here's why:
* Different Missions: Space probes are designed for specific missions. Some explore the outer solar system (like Voyager), some study Mars (like Curiosity), and some focus on Venus (like Magellan).
* Ongoing Exploration: Space exploration is an ongoing process. New probes are constantly being launched, so the list of planets visited is always changing.
To answer your question more directly:
There are several planets that have not been visited by a probe that landed on the surface. Some examples are:
* Uranus: While Voyager 2 flew by Uranus, no lander has touched down.
* Neptune: Similar to Uranus, Voyager 2 flew by Neptune, but no lander has been sent.
* The Ice Giants: These are the outermost gas giants, which are incredibly difficult to reach and study.
It's important to remember: Just because a probe hasn't landed on a planet doesn't mean we know nothing about it. Flyby missions provide valuable information about the planet's atmosphere, magnetic field, and moons.
