Question: When did exploration to the inner solar system begin?
Disambiguated questions and answers: question: When did exploration to the inner solar system technically begin with the launch of the first lunar flyby satellite?
When did exploration to the inner solar system technically begin with the launch of Pioneer 5 for interplanetary space investigations?
When did exploration to the inner solar system technically begin with the launch of Mariner 2, which resulted in the first successful flyby of Venus?
answer: 2 January 1959
11 March 1960
27 August 1962
Natural Questions answer: 1959 (from the Wikipedia article "Discovery and exploration of the Solar System")