Yes, the Voyager 2 probe visited all four gas giant planets; Jupiter, Saturn, Uranus and Neptune. It flew by Neptune in 1989.
No spacecraft from Earth has ever landed on Neptune.
Just one.
Voyager 2, which flew by the giant planet in 1989.
Voyager 2 flew by Neptune in 1989, coming within 30,000km of the planet.
As of 2011, only one spacecraft has passed relatively close to Neptune. The Voyager 2 probe visited Neptune in 1989, having previously passed Jupiter, Saturn, and Uranus. Voyager 2 took the first close-up photos of the Neptunian moon Triton, and discovered five inner moons: Naiad, Thalassa, Despina, Galatea and Proteus.
The most successful space probe launched to Neptune was Voyager 2. It made its closest approach to Neptune in 1989, providing valuable data and images of the planet and its moons. Voyager 2 remains the only spacecraft to have visited Neptune.
Nobody knows for sure. If they do know, they aren't telling.
Only one through 2009. The Voyager 2 probe visited Neptune in 1989, having previously passed Jupiter, Saturn, and Uranus. Voyager 2 took the first close-up photos of the Neptunian moon Triton and discovered 5 new inner moons.
A spacecraft left earth in late 1957 and returned in early 1958. Other than human spacecraft, no alien space craft has ever left or come to visit our planet, that we know of. It is possible some alien space craft may have visited earth millions of years ago. It is highly unlikely any craft has done so within the past few centuries.
Nobody. It is impossible to walk on Neptune as there is no solid surface. The only object where people have walked other than Earth is the moon.
Every known spacecraft began on earth and went to other places. That's also true of every known drawing, component, fragment, subsystem, and model of spacecraft. Few of them ever returned to earth.
Yes. Every spacecraft ever made by humans originated on Earth and most never went farther than an orbit around Earth. Many have returned to the surface.