With its beautiful rings (280,000 km across), impressive size (120,000 km diameter at the equator), and extensive number of moons (more than 60), Saturn has always been fascinating. But, because it’s so far away (ten times farther from the Sun than we are) it wasn’t always a realistic target for observation and experimentation. The first attempt to reach Saturn was in 1973, when NASA sent Pioneer 11 on its way. It arrived six years later, having navigated the dangerous asteroid-belt that lies between us and Saturn, but with only basic instrumentation on board it wasn’t able to gather much scientific data.
A larger spacecraft with better instruments was then sent on the same journey: Voyager. This did a fast fly-by in November 1980, so only gave us a glimpse of Saturn, its rings, and its moons. Then, 17 years later, in October 1997, a much more powerful mission was launched: Cassini–Huygens. Cassini was the NASA-developed Saturn orbiter, and Huygens was the European-built probe that sat on-board, which would eventually descend on to the surface of Saturn’s biggest moon, Titan.
Cassini will come to an end on 15th September 2017, when it makes its final approach to Saturn, diving in to the atmosphere (sending data as it goes), and finally burning up and disintegrating like a meteor. To mark this occasion we have brought together a selection of the discoveries the mission has made over the years, in a reading list below.
An overview of the mission
From the early attempts to explore Saturn and its moons to the Cassini–Huygens mission, there have been trials and tribulations along the way. The Cassini–Huygens mission was not only challenging, but expensive, so it was clear international collaboration (and sharing of costs) was essential, as was maintaining political support for the project.
“Big Planets, Dwarf Planets, and Small Bodies” in Mankind Beyond Earth: The History, Science, and Future of Human Space Exploration by Claude Piantadosi
The magnetosphere of a planet is the volume of space that surrounds it, within which there are dominating magnetic fields and radiation belts. The first space missions that went to Saturn (Pioneer 11 and Voyager) helped scientists begin to understand Saturn’s magnetosphere, but the Cassini mission has dramatically enriched our understanding of these. For example it discovered that Saturn has two belts (the main and the new), which are interrupted by its rings.
Titan has a number of Earth-like qualities and is the only (natural) satellite in our solar system that has a dense atmosphere. The Cassini mission has given us answers to a lot of the outstanding questions that we had about this atmosphere – showing it to be similar to our own, with temperatures and pressures at Titan’s surface meaning that methane can condense to a point where it creates clouds, and falls as rain.
Enceladus’s jets of water
“Genesis 2.0? SETI and Biology” in Science, Religion, and the Search for Extraterrestrial Intelligence by David Wilkinson
Are we alone? Are there other life forms out there, in the Solar System? A case for possible (primitive) life was discovered by the Cassini mission, when it did a fly-by of Enceladus (another moon of Saturn) and discovered jets of water vapour shooting out into space. This means that there are reservoirs of water under the moon’s icy surface, with further analysis showing simple organic molecules within a salty ocean.
“Epilogue, 2001–2004” in Into the Black: JPL and the American Space Program, 1976-2004 by Peter J. Westwick
The Cassini mission has provided some incredibly close-up and striking images of Saturn and its moons, with a camera that was five times the resolution of the one on Voyager (plus a radar to see through Titan’s atmosphere). There are fascinating images of geysers shooting from Enceladus’s south pole, beautiful images of Saturn’s rings (including one with Saturn’s shadow falling on them), and a zoomed-in view of Epimetheus (another of Saturn’s moons).
Featured image credit: ‘The Day the Earth Smiled’ by NASA/JPL-Caltech/SSI. Public Domain via Wikimedia Commons.