Pioneer and Voyager

Four unmanned spacecraft were sent past the giant planets, two Pioneers and two in the Mariner series. Pioneer 10 and Pioneer 11 were launched in 1973. Pioneer 10 sent back the first close-up pictures of Jupiter’s cloud systems, with its storms so big that they would cover the entire Pacific Ocean. Since then, Pioneer 10 has been headed out of the Solar System. Its power fading, it continued to send data about deep space and was last heard from in 2003. Meanwhile, Pioneer 11 swung by Jupiter on its way to Saturn, giving us our first detailed views of the famous rings. Pioneer 11 is also on a trajectory out of the Solar System, but, since 1995, Earth has been out of range of its antenna.

The Mariner ships had more powerful instruments and bigger cameras than the trailblazing Pioneers. Before launch in 1977, the Mariners were renamed Voyager 1 and Voyager 2. Within a few days of approaching Jupiter, Voyager 1 took some of the most surprising pictures ever seen. They showed that Jupiter’s moon Io (pronounced EYE-oh) was not a dead and dormant orb like our Moon. Instead, Io is covered with recent lava, and huge, new volcanoes are constantly erupting!
Voyager 1 went on to Saturn. Its target there was the moon Titan, which is the only moon with a thick atmosphere. Pictures from Voyager 1 showed that the atmosphere is thick enough to shroud the surface from view. Aiming for Titan meant that Voyager 1 could not get the proper gravity boost from Saturn to con- tinue the Grand Tour. So, Voyager 1’s path took it out of the solar system without going near Uranus and Neptune.

Voyager 2 visited all the giant planets—the only spacecraft to realize the complete Grand Tour. After taking fabulous photographs of Jupiter and its moons in 1979, then of Saturn and its moons in 1981, Voyager 2 went on to Uranus in 1986 and Neptune in 1989. Pictures showed subtle details in the planets’ clouds, as well as dramatic features on their families of rocky and icy moons.

Like the plucky little Pioneers, both Voyagers are traveling so fast that the Sun’s gravity can never stop them. Their power supplies should be fine until at least the year 2020, so scientists still have many years of data to look forward to from deep space. Already many billions of miles from home, neither the Pioneers nor the Voyagers are aimed at any nearby stars. But they will continue on as citizens of the galaxy forever. Who knows what adventures lay ahead for them?