Defining "space exploration" can be tricky. Here are a few key events and their years:

* 1957: The launch of Sputnik 1, the first artificial satellite, is often considered the beginning of the Space Age.

* 1959: Luna 2, a Soviet probe, became the first spacecraft to reach the surface of the Moon.

* 1961: Yuri Gagarin became the first human in space aboard the Soviet spacecraft Vostok 1.

* 1969: Neil Armstrong and Buzz Aldrin became the first humans to walk on the Moon as part of the Apollo 11 mission.

So, depending on what you consider the first space exploration, the answer could be 1957, 1959, 1961, or 1969.