They are sending legos* to Jupiter.
"The specially-constructed aluminium Minifigures are the Roman god Jupiter, his wife Juno and ‘father of science’ Galileo Galilei." --from the Lego press release
How cool is that? Legos, space exploration, and Greco-Roman mythology all tied up together in one event. I don't have anything else to say on the matter, I think "cool" nicely summarizes the whole thing.
*I am well aware that the proper term is "Lego", but damn if I didn't grow up calling them "legos", and I'll not change now. Anyway, it's like Trekkie vs. Trekker and you're just getting angry about something on the Internet.