All the terrestrial visitors to Jupiter so far have been robotic probes. All but one were fly-by missions which continued to other destinations. It’s impossible to land because there’s no solid surface, the gravity is too high, the climate too wild and the radiation lethal. The only practical place in the Jovian system where humans could land is Callisto, at a reasonably safe distance from Jupiter and with a stable surface. Astronauts are not likely to go there for a long while yet, if at all.
The first probes to brave the Jovian environment were Pioneers 10 & 11 which arrived at their destination about a year apart, in 1973 and ‘74. The Pioneers gave astronomers their first close-up images of Jupiter and detailed measurements of its radiation and magnetic field. Pioneer 10 is of particular note in being the first spacecraft to cross the asteroid belt, arrive at Jupiter and then venture into the outer reaches of the solar system. It carries a gold plaque showing two human figures next to a diagram of the solar system, marking where they and Pioneer come from.
Both probes continued sending information from the outer solar system for many years. Contact was eventually lost with Pioneer 11 in 1995 and Pioneer 10 in 1997, by which time a further four missions had reached Jupiter. Pioneer 10 is heading in the direction of Aldebaran, a bright, red giant star in the constellation of Taurus the bull. You’ll easily be able to see Aldebaran during NAW, so spare a thought for the tiny probe billions of miles from home and heading for the stars.
The intrepid Voyagers took Jovian exploration a stage further in 1979 by making detailed studies of the Galilean moons. It was Voyager 1 that revealed Io’s fiery volcanic activity and later on looked back to image Earth as a tiny pale blue dot, suspended in infinite space. Both Voyagers are still in touch with Earth as of 2012 and by now are in the heliopause, beyond the fringes of the solar system. Voyager 1 is the record holder for most remote man-made object, heading more or less towards Sirius, the brightest star in the night sky.
Next up in 1990, Ulysses was a solar probe which used Jupiter’s gravity to establish a long looping orbit around the Sun. In passing Jupiter, Ulysses was able to confirm and add to information originally provided by the Pioneers and Voyager.
Launched in 1989, Galileo was the one probe that stayed – for good. At the end of its mission in 2003 it was deliberately sent plummeting into Jupiter’s atmosphere to avoid any possible contamination on Europa, which might just harbour life. During its mission Galileo made highly detailed images and measurements of both Jupiter and the Galilean moons. In 1994, Galileo was ideally placed to witness the spectacular demise of comet Shoemaker-Levy 9, as it plunged into the Jovian atmosphere.
The Cassini probe followed in 1997, passing Jupiter in 2000 on its way to Saturn. During its fly-by, Cassini transmitted back detailed images of the Jovian atmosphere and revealed that air currents in the zones are sinking while those in the belts are rising
Into the 21st century, the New Horizons probe was launched in 2006 on the fastest trajectory ever achieved by a spacecraft and passed by the Jovian system in 2007, on an epic journey to encounter Pluto in 2015. Again, New Horizons added to the information first gathered by the earlier probes.
Juno, the latest mission, was launched in 2011 and is due to arrive at Jupiter in 2016. The main mission objective is to study and measure Jupiter’s magnetosphere and composition.
JUICE is a planned mission by the European Space Agency scheduled for launch around 2022. The Jupiter Icy moon Explorer is intended to analyse the Galilean Moons in unprecedented detail and determine whether or not Europa, or any of the other three moons, has a sub-surface ocean as conjectured. If so, this will pave the way for future probes seeking life.