The Juno spacecraft will become the seventh robotic vehicle to visit Jupiter when the observatory speeds past the planet on July 4. This vehicle, packed with a bevy of scientific instruments, will join a short list of six other space vehicles that have visited the largest planet in the solar system over the last 45 years.
Pioneer 10 was launched to the Jovian system in 1972, reaching its destination in December 1973. The NASA mission measured concentrations of hydrogen and helium gas in the atmosphere of the giant world. The vehicle discovered the powerful magnetosphere surrounding the globe, and was the first spacecraft to endure the rigors of Jupiter's powerful radiation belt.
The year 1979 saw a pair of revolutionary observatories fly past Jupiter — Voyager One and Two. These vehicles, managed by NASA, soared past the gas giant in March and July of that year. As the observatories soared past the world, a look at the dark side of Jupiter revealed massive lightning strikes taking place across the face of the globe. The Voyager observatories were able to photograph the surfaces of many of Jupiter's moons, allowing researchers to develop maps of the satellites for the first time. The innermost moon of Jupiter, Io, was found to be geologically active, with volcanoes erupting on the surface. Due to advances in technology since the Pioneer visit, the Voyager mission was able to return far more data than its predecessor. Both vehicles are now traveling out of the solar system, to interstellar space.
"The prime mission science payload consisted of 10 instruments (11 investigations including radio science). Only five investigator teams are still supported, though data are collected for two additional instruments. With the exception of the Voyager 1 PLS instrument, all of the above are working well and are capable of continuing operations in the expected environment," Jet Propulsion Laboratory reports.
Galileo became the first spacecraft to orbit Jupiter, after being launched to that world in 1989. Since its arrival in the Jovian system, the observatory has carried out careful examinations of the gas giant, as well as its dozens of attendant moons. The vehicle was named in honor of Galileo Galilei, the Italian astronomer who carried out the first telescopic observations of the system during the early 17th century.
Launched in October 1990, the Ulysses spacecraft passed by Jupiter on its way toward a polar orbit over the sun. As the vehicle swung through the massive gravitational well of Jupiter, the observatory found the solar wind affects the magnetosphere of the world to a much greater extent than astronomers had predicted.
On June 30, 2016, Juno passed into the magnetic field of Jupiter, marking the spacecraft's imminent arrival at the giant world.
"If Jupiter's magnetosphere glowed in visible light, it would be twice the size of the full moon as seen from Earth," said William Kurth of the University of Iowa.
Juno promises to answer a number of questions investigators are currently asking themselves about the largest planetary body in the solar system. If history is any guide, discoveries by the mission will reveal additional questions.