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This question does not seem very specific.
If you are referring to the planets for which the technology needed to reach them does not exist, I would say that we are not able to visit any planet except maybe Mars.
If you are referring to the planets for which the equipment to reach them does not exist, that would be every planet there is, including Mars.
We have the potential to reach at least Mars, but nobody has gone and done it yet (it would cost a lot of money)