Sending a spacecraft to Mercury is hard.

First of all, it gets pretty hot that close to the Sun—about 430 degrees Celsius—which is bad for a space robot's electronics.

Secondly, it's hard to get there. Any spacecraft visiting Mercury has to shed a huge amount of energy as it spirals in towards the Sun to match Mercury's orbital trajectory.

In the 1960s, as NASA prepared to launch humanity's first mission to Mercury, an Italian mathematician-engineer named Giuseppe "Bepi" Colombo proposed a way for a spacecraft to enter a 176-day orbit around the Sun—double the orbital period of Mercury. This allowed the mission, Mariner 10, to successfully fly past Mercury three times in 1974 and 1975.

Mercury then remained unexplored for three-and-a-half decades, until NASA's MESSENGER probe arrived for a four-year stay in 2011.

Now, we're going back. Next year, Europe and Japan are sending a pair of spacecraft to Mercury in hopes of answering outstanding questions about our innermost planet, as well as the formation of the solar system. The mission is named BepiColombo, in honor of the person who helped make the initial reconnaissance of Mercury possible, and it just took another step next year's October 2018 launch.