Water
yes, spacecraft have visited Mars, but the results haven't always been positive. More than half of the attempts to send a spacecraft to the planet have failed.
Depends on whether you say Pluto is a planet or not. If you say it isn't, then there are no planets that haven't been visited by a spacecraft. If you say it is, then there is one that hasn't been visited yet, but one is on the way.
yes
Mars.!!! However, spacecraft have landed on Venus, but the atmosphere on Venus is such that spacecraft are crushed/collpase. So no exploration has been done on Venus.
1 time Neptune has been vist
As of yet, there have been no manned Mars spacecraft at all.
hi
Explorer Missions
yes
no but one is getting there
yes several
oceanic crust
yes, spacecraft have visited Mars, but the results haven't always been positive. More than half of the attempts to send a spacecraft to the planet have failed.
Depends on whether you say Pluto is a planet or not. If you say it isn't, then there are no planets that haven't been visited by a spacecraft. If you say it is, then there is one that hasn't been visited yet, but one is on the way.
yes
yes
Billions.