Respuesta :
"The planet Mars, wich is Earth's nearest neighbor, has long fascinated scientists as well as science-fiction fans."
We use here commas to connect two separated clauses one beign "the planet mars has long fascinated scientists as well as science-fiction fans and the other is planet Mars being Earth's nearest neighbor.
The correct option is:
The planet Mars, which is Earth's nearest neighbor, has long fascinated scientists as well as science-fiction fans.
Explanation:
There are defining and non-defining relative clauses. Defining relative clauses provide essential information, whereas non-defining can be removed without altering the meaning of the sentence.
In this case, "which is Earth's nearest neighbor" can be removed without changing the meaning.