|Jupiter is a behemoth of planetary mass in our solar system. Here you can see the relative masses of the 8 planets. (image from Das steinerne Herz on Wikipedia)|
It was Galileo's discovery of four of the moons of Jupiter in 1610 and his writing of them that nearly caused the Catholic Church to murder Galileo (the idea that there could be moons orbiting other planets was certainly considered blasphemy against the church at that time). Below you can see a page from the Sidereus Nuncius ("Starry Messenger"; Galileo's 1610 book on his astronomical observations), where Galileo drew Jupiter and the moons he had discovered:
The Pioneer 10 spacecraft was the first extension of humanity to fly by Jupiter back in 1973. Here's one of the images taken during that encounter with the giant world. Pioneer 10 was the first spacecraft to measure the radiation and magnetic fields surrounding Jupiter. It was also the first to take images of the moons of Jupiter up-close. Pioneer 10 passed within 81,000 miles of the cloudtops of Jupiter on it's flyby over 40 years ago.
Jupiter has since had several other spacecraft go zooming by, most of which at least took pictures if not full-on collecting data and targeting Jupiter and its moons for observation; for instance, check out this table I stole from Wikipedia on spacecraft that have flown by along with the dates of closest approach and the minimum distance from Jupiter at that time:
|Pioneer 10||December 3, 1973||130,000 km|
|Pioneer 11||December 4, 1974||34,000 km|
|Voyager 1||March 5, 1979||349,000 km|
|Voyager 2||July 9, 1979||570,000 km|
|Ulysses||February 8, 1992||408,894 km|
|February 4, 2004||120,000,000 km|
|Cassini||December 30, 2000||10,000,000 km|
|New Horizons||February 28, 2007||2,304,535 km|
The only spacecraft so far to be sent into orbit of Jupiter was the Galileo Spacecraft, which operated in the Jovian system for over 8 years (from its arrival in December of 1995 until we crashed it into Jupiter (something we like to call "de-orbiting") in September of 2003). Galileo was used to study Jupiter's atmosphere and rings and to image and study the volcanoes on Io. Galileo discovered that Ganymede has its own, very strong magnetic field and really gave us most of the best data from which we have concluded that there is likely a deep subsurface ocean on Europa. The Galileo spacecraft really unlocked Jupiter and set the grounds for future spacecraft to visit that giant world.
|An artist's concept of the Galileo spacecraft at Jupiter, with Io's volcanoes erupting nearby|
Following Juno, there are two missions in the works for studying the icy moons of Jupiter. JUICE (the Jupiter Icy Moon Explorer) is an ESA mission slated for launch in 2022. JUICE is designed to study primarily Ganymede and Callisto, though it should also fly by Europa a couple of times as well. A NASA mission set for launch on the early 2020s (likely 2022, as of now) is also in the works. The mission is currently called the Europa Multiple-Flyby Mission, though that name will surely change when the mission is more fully developed. This mission will focus on studying Europa. It will tell us about the surface processes and composition of Europa, will tell us a bit about the internal geology and composition of this moon, and, most importantly for astrobiology, will seek to determine the existence of Europa's ocean and determine what it can about the composition and possible surface-interactions of this ocean.
Though JUICE and the Europa Multiple-Flyby Mission will target the icy moons of Jupiter, they will teach us a lot about the Jovian system in general (like how Jupiter's magnetic field and the chaotic whipping of particles through that field effect the moons of Jupiter). Taken along with Juno, the next couple of decades of research on Jupiter should be highly revealing, telling us a lot about the king of the planets but also helping us to uncover new mysteries and new questions about this behemoth in our solar system.
In closing out this post, here is a quote about Jupiter, the god, from Ovid:
Jupiter Drawing, from Kelvin Ma at Wikipedia