Pioneer 11 swept past Saturn 43 years ago today

Pioneer 11: Golden ball of Saturn, surrounded by nearly edgewise rings, and a little dot of a moon.
Pioneer 11 caught this image of Saturn when the spacecraft was 1,768,422 miles (2,846,000 km) from the planet. It shows Saturn and its largest moon Titan. Image via NASA.

Pioneer 11 swept past Saturn 43 years ago today

On today’s date – September 1 – in the year 1979, NASA’s plucky Pioneer 11 spacecraft became the first earthly craft ever to sweep past the ringed planet Saturn. Incredibly, the spacecraft came within 13,000 miles (21,000 km) of Saturn, crossing the plane of the planet’s rings. In the process, Pioneer 11 found a new ring for Saturn – now called the “F” ring – and two new moons. In fact, the spacecraft almost smacked into one of these unknown moons, as it soared past.

Passing Saturn – and passing it safely – was an astounding achievement. And indeed, Pioneer 11 was a true pioneer. It went where no earthly spacecraft had gone before.

Generally speaking, Pioneer 11 did what pioneers always do. It laid the groundwork for those that followed. That included the two more sophisticated Voyager spacecraft, which launched from Earth in 1977 and visited Saturn in 1980 and 1981. Part of Pioneer 11’s job was to test a trajectory near Saturn’s rings, to see if it was safe for the upcoming Voyager mission. So, Pioneer 11 passed through the Saturn ring plane, at the same position that the Voyager probes would use some years later. The idea was that – if there were faint ring particles that could damage a probe in that area – mission planners would prefer to let Pioneer 11 take the damage, rather than the Voyagers.

Cassini mission

In addition, Pioneer 11 also preceded the wonderful Cassini mission, which orbited Saturn – weaving in and among its moons – from 2004 to 2017. To be sure, Cassini provided unprecedented and spectacular views of Saturn and its rings and moons.

The Voyagers were cutting-edge. And Cassini returned images beyond anyone’s wildest dreams.

But Pioneer 11 paved the way.

Painting of a giant man, encompassing the planet Jupiter, casting a spacecraft onward from a sling.
View larger. | This fanciful illustration was an early attempt to illustrate the concept of gravity assists – or gravitational slingshots – the use of a planet’s strong gravity to alter a spacecraft’s path and speed. The maneuver is now widely used by interplanetary spacecraft to save propellant and reduce expense. But, in the 1960s and ’70s, it was a new way of thinking. Image via Pioneer: First to Jupiter, Saturn and Beyond.

The 2 Pioneers had different missions

There were two Pioneer spacecraft. The other was called Pioneer 10. Both Pioneers visited Jupiter, and Pioneer 11 went on to Saturn, to investigate its rings and moons.

Scientists said that Pioneer 11 enabled them to get a sense of Saturn’s internal composition. As a matter of fact, Saturn is not very dense. So it’s long been said that, if you could find an ocean large enough to hold it, Saturn would float on water. Pioneer 11 showed Saturn likely has a relatively small core for an outer gas giant world. In fact, with only 10 times Earth’s mass, Saturn was found by Pioneer 11 to be mostly liquid hydrogen.

Diagram of orbits of outer planets with spacecraft paths drawn in.
View larger. | In the 1970s, a battle of ideas raged in the U.S. space program. Should we focus on manned spaceflight? Or should we put our (limited) resources into small, relatively inexpensive interplanetary probes? A rare alignment of the outer planets in the late 1970s and ’80s provided an opportunity to explore the outer solar system with relative ease, using gravity assists to send spacecraft from one planet to the next. In the end, in part thanks to this alignment, small robotic planetary explorers won the day. And so we had the Pioneer missions – and later the more advanced Voyager missions – a Grand Tour of the outer solar system. Image via Secretsofuniverse.

Pioneer 11 (probably) still sails on

Pioneer 11’s last transmission reached Earth on September 30, 1995. And so the mission has ended. But Pioneer 11 is one of five spacecraft whose trajectories ultimately will carry them out of our solar system. So, unless something has stopped it (highly unlikely!), Pioneer 11 is still sailing outward, away from Earth, into the depths of space.

It’s moving in the direction of our constellation Scutum. Scutum is next to Sagittarius, which is in the general direction of the center of our Milky Way galaxy. The craft will pass near the star Lambda Aquila some four million years from now.

Oblique view of outer planet orbits with Pioneer's path from Earth to Saturn.
Here’s Pioneer 11‘s trajectory, from launch in 1974 to its Saturn encounter in 1979 … and beyond. Image via NASA.
A spacecraft with a round shape, two legs and a long antenna, against background of Milky Way and stars.
Artist’s concept shows Pioneer 10 as it leaves the solar system. Pioneer 10 relayed its last, weak message to Earth on January 22, 2003, from a distance of 7.3 billion miles (11.7 billion kilometers). Image via NASA.

The Pioneers carry plaques

By the way, like the Voyagers, the Pioneers carry a message from humanity to the stars. They each carry a gold-anodized aluminum plaques, showing the nude figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.

Would an advanced race be able to interpret humanity’s message? It’s hard to say. But – like the Voyagers’ golden records – the Pioneer plaques helped raise the consciousness of human beings back on Earth.

Drawing of man, woman, diagram of solar system, other informative drawings.
The Pioneer plaque, which Carl Sagan helped design and place aboard the 1st 2 spacecraft ever to leave Earth for interstellar space, via Wikimedia Commons.
The plaque showing male and female human figures, and more, mounted between spacecraft struts.
Here’s the plaque attached to Pioneer 10. The plaques were attached to the spacecraft’s antenna support struts in a position that would shield them from erosion by interstellar dust. Image via Wikimedia Commons.

Bottom line: Pioneer 11 came closest to Saturn on September 1, 1979.

Read more: Pioneer 11: Watching the Saturn watchers

Pioneer: First to Jupiter, Saturn and Beyond

Visit Cassini spacecraft image Hall of Fame

September 1, 2022

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