Space Missions to the Outer Planets and their Moons The new era of space exploration has offered us the possibility of answering some of the key questions related to possible life, by means of sophisticated spacecraft travelling through our solar system including the outer planets and their moons. We have learned much about the outer regions of the solar system during the past three decades, first by means of the NASA Pioneer spacecraft, of which Pioneer 10 is now nearly 12 billion kilometres from the Earth, but still active and in radio contact with us! An incredible wealth of data, including many fantastic images, was collected by the two Voyager spacecraft, that visited all of the outer planets, except Pluto. The fly-bys took place in 1979 (Voyager 1 and 2 at Jupiter), 1981 (Voyager 1 and 2 at Saturn), 1986 (Voyager 2 at Uranus) and 1986 (Voyager 2 at Neptune). More recently, the NASA Galileo spacecraft has returned to Jupiter for an extended visit. It has provided us with fascinating images of the inner moons of this planet, revealing in great detail the various structures on their complex surfaces and measuring their physical properties (e.g., mass, size, temperature, composition, magnetic field, etc.). Space Missions to Titan and Europa One spacecraft is already on its way towards Saturn: the NASA/ESA Cassini/Huygens mission that is destined to study the neighbourhood of the Saturnian system. One of the main targets of this mission is to explore Titan, Saturn's largest natural satellite and one of the most intriguing objects in the Solar System. Another spacecraft, the Europa Orbiter, will visit Europa, Jupiter's satellite, sometime after 2006. Towards Pluto? There has been much discussion about a mission to the outermost planet, Pluto, and various proposals have been made, including the Pluto-Kuiper Express, but no final decision has been made yet.

The NASA Voyager 1 and 2 spacecraft were launched in 1977 and visited the four large outer planets, Jupiter, Saturn, Uranus and Neptune. They carried a large number of scientific instruments that gathered an enormous amount of data about these planets and their moons, and also about interplanetary space. The Voyagers are now heading towards interstellar space and it is expected that it will be possible to keep radio contact with them until about 2020.