"Each of the missions that we do are providing unique and very important information," said Juno's principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio, just before Juno's August 2011 launch. "Some of those earlier missions were reconnaissance, so we could figure out what are the right questions, and they essentially led us to ask the questions that we have with Juno." [Photos: NASA's Juno Mission to Jupiter]
Here's a rundown of all the manmade objects sent to visit Jupiter so far:
The craft flew within 124,000 miles (200,000 kilometers) of the tops of the clouds covering the gas giant. It made a number of revelations about the gas giant, including measurements of the intense radiation in the environment of Jupiter.
Pioneer 10 is currently on a trajectory to leave the solar system, traveling toward the outskirts of the Milky Way in the direction of the star Aldebaran. Communication with the spacecraft was lost in 2003.
This probe captured detailed images of the Jovian Great Red Spot, as well as the planet's poles, and measured the mass of Jupiter's moon Callisto.
Humans lost the ability to communicate with Pioneer 11 in 1995, but the probe is still traveling toward the center of the galaxy in the direction of the constellation Scutum.
Voyager 1 is now on its way out of the solar system and is currently the most distant manmade object from Earth, at about 69 times the distance from the sun to our own planet.
The probe is still operating on an extended mission to study the boundary between the solar system and interstellar space. [5 Facts About NASA's Voyager Spacecraft]
While in orbit, Galileo dropped a probe down to the surface that measured the temperature, wind speeds and pressure of Jupiter's atmosphere as it descended. Galileo's mission was extended to study Jupiter's moons Io, Europa, Ganymede, and Callisto, and it revealed a trove of secrets about these satellites, including the presence of a salty ocean under Europa's surface and an iron core and magnetic field on Ganymede. Galileo studied Jupiter until 2003, when it was decommissioned and sent on a suicide mission to crash into Jupiter's surface in order to avoid contaminating any of the Jovian moons with bacteria from Earth.
However, the flyby was enough for Ulysses to gather some helpful measurements of Jupiter's intense magnetic and radiation field. Ulysses' mission ended in June 2009. [Video: Key to Solar System's Origins Locked Inside Jupiter]
The probe's high-resolution cameras caught 26,000 dazzling images of the Jovian atmosphere during its months-long flyby. These photos helped scientists revise their understanding of the red and white bands of gas around the planet.
The Huygens probe dropped into Saturn's moon Titan in 2005, and the Cassini probe is still orbiting Saturn.
The Jupiter visit was in fact an essential part of New Horizons' mission, as the giant planet's gravity provided a once-in-a-lifetime opportunity to slingshot a craft on toward Pluto. During the five-month flyby, New Horizons refined calculations of the orbits of Jupiter's inner moons, and took the first spacecraft photos of the planet's Little Red Spot.
The mission will build on all those that have gone before, hopefully helping scientists fill in the gaps in their understanding of Jupiter's formation and evolution, as well as the history of the solar system in general. The spacecraft is outfitted with instruments to study in detail the gas giant's atmosphere, magnetosphere and gravitational field. Scientists will investigate the auroras that rage on Jupiter's poles, and construct a 3-D map of the planet's full environment.