As far as anyone knows, no human being has ever been to an unknown planet. We have not yet set foot on any other planet (although we have walked on another world, our moon) of our solar system. We will go to other planets though, some day.
This is impossible to answer for a planet with unknown conditions or characteristics.
The largest unknown planet in our solar system is currently referred to as Planet Nine or Planet X. It is thought to be a large planet located beyond Pluto's orbit, but it has not been directly observed yet.
No. No planet other than Earth has been visited by men. We made it to the moon, but no further.
john William has explored the planet mercury... but no one has been sent out to this planet
There have been no manned missions to Mercury.
Planet X has not been confirmed to exist, so its size is unknown. Jupiter is the largest planet in our solar system, with a radius of about 69,911 km.
planet x is unknown but is farther than Pluto
There are very few on this planet that are lucky enough to have been given a phone.
No one has every been to Mercury. The furthest man has been is to the Moon. Probes have been sent to Mercury
It is not definitively known whether the unknown planet has a liquid region in its interior without further exploration and analysis. The presence of a liquid region could depend on factors such as the planet's composition, temperature, and geological activity.
It is currently unknown
As of 2014, humans have not set foot on the planet Mercury. To date, the only probes sent have been Mariner 10 which did a flyby, and the MESSENGER orbiter; both probes from NASA.