Answer: The Moon

The Soviet Union managed to accomplish three space exploration firsts with a single spacecraft: Luna 1. The small spacecraft was intended to be a lunar impactor, destined to slam into the surface of the Moon and report data back to Earth, but thanks to an error along the way, it was destined for a much longer trip.

During the launch sequence, an incorrectly timed upper stage burn caused Luna 1 to miss the Moon. In the process, it became the first spacecraft to reach the vicinity of the Moon (but, unfortunately, not land on it as intended). In missing the Moon, it also became the first spacecraft to leave geocentric orbit and eventually came to enter a heliocentric orbit (becoming the first man-made object to do so). Renamed Mechta (or Russian for “Dream”), it now orbits the Sun in an orbit between that of Earth and Mars.

Despite missing its intended target, Luna 1 proved quite useful and was able to report back data about the Moon as it passed by, obtain data about the Van Allen radiation belt, take direct measurements of the solar wind, release sodium gas for observing the behavior of gas in space (as well as helping track the satellite), and also marked the first instance of radio communication at a distance of a half-million kilometers.