The Mariner Ten and the Messenger
All spacecraft (from Earth) that have visited Mercury have been robotic. There were no human passengers. The chances are near zero that a stowaway microbe would have survived the long journey.
All of the eight planets have been visited or orbited by space probes.
It's not clear what you mean by "visited", here. All man-made spacecraft ORIGINATED from Earth. Some of them later RETURNED to Earth as well, and quite a few of them were designed to STUDY Earth (for example, weather satellites).
Nobody knows for sure. If they do know, they aren't telling.
It's the closet and rather similar to the earth.
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.
The space shuttle is an Earth orbit vehicle. No humans have ever travelled to any body other than the Moon (from 1969 to 1972). All other space exploration has been by unmanned probes.
The first American spacecraft which orbited the earth was called The Mercury Friendship 7, and the astronaut was a famous person his name was John Glenn, he was a senator for many years later.
Mercury
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.
Mercury Friendship 7 (John H. Glenn, USA) was the first spacecraft to orbit the Earth three times.
A spacecraft without people on board is called an unmanned spacecraft or a robotic spacecraft. These types of spacecraft are operated remotely from Earth or operate autonomously.