10 Interesting Facts about the Missions to Saturn

Image Credit: Saturn taken by Cassini in July 2008

Saturn has been observed since prehistoric times, with the planet having played a major role in all major ancient cultures and religions throughout history. The ancient Babylonians, for instance, kept records describing detailed observations of Saturn, while in the modern Greek language, the planet is still known as Kronos, the Greek equivalent of Saturnus, the ancient Roman god of agriculture.

Saturn is a long way from Earth and until Uranus was discovered in 1781, followed by Neptune in 1846, it was considered the most distant known planet. Nevertheless, while telescopic observations over the last 200 hundred years or so have revealed many fascinating aspects of “The Ringed Planet”, the first real scientific knowledge of the vast Saturnian system only became available during the past few decades. Below are listed 10 interesting facts about the various missions to Saturn, starting with the early fly-by missions.

Pioneer 11 fly-by in 1972

The image below shows the first close-up view of Saturn taken by the Pioneer 11 probe in September of 1979. On this occasion, the Pioneer craft approached Saturn to within 20,000 km of the planet’s cloud tops, although the resolution of this image is too low to discern any surface detail on the planet or the rings. Nonetheless, the Pioneer fly-by discovered the exceedingly tenuous F-ring, and provided data that the dark gaps between the major rings are in fact filled with fine-grained dust particles, and are therefore not empty as was previously thought.

P11 Saturn

Voyager 1 fly-by in 1980

While both Voyagers made significant contributions to the body of knowledge about Saturn, Voyager 1 took the first high-resolution images of the planet in November of 1980, as well as of its rings and satellites. In particular, Voyager 1 discovered that the atmosphere of the planet’s moon Titan couldn’t be penetrated by light in visible wavelengths. In the case of Voyager 1, the Titan fly-by served as a gravity assist to propel the craft out of the solar system’s plane.

Voyager 2 fly-by in 1982
When Voyager 2 arrived at Saturn almost a year later in August of 1982, it discovered a rotating hexagonal feature almost at the planet’s North Pole. Each side of the feature is about 13,800 km (8,600 mi) long (longer than Earths’ diameter), and the whole structure rotates with a period of 10h 39m 24s, which largely coincides with the planet’s radio emission period. A clearer photo of the phenomenon was subsequently taken several decades later by NASA’s Cassini mission, with the image shown below captured in 2014.

Saturn North Polar Hexagon

While the nature and origin of this feature remain unknown, most investigators believe that it is the result of a standing wave pattern high in the planet’s atmosphere, since laboratory experiments have produced similar polygonal (multi-sided) wave patterns in various fluids that rotate at different speeds. The Voyager 2 fly-by of Saturn also served as a gravitational assist to propel the craft on its way to Uranus.

Cassini–Huygens probe in 2004

Known simply as “Cassini”, this probe had been described as an unqualified success, a mission of firsts, and in many other glowing terms, since it exceeded its design life by almost a full 16 years. In total, the craft spent 19 years and 335 days in space, of which 13 years and 76 days were spent in orbit around Saturn after a journey of 6 years and 261 days.

Launched on October 15, 1997, Cassini’s primary mission was planned to have a duration of only four years, but this was extended twice after some political wrangling between NASA, the European Space Agency, and the Italian Space Agency, the three partners that designed, built, and launched the craft. The first mission extension was named “Equinox” and lasted for a period of 2 years and 62 days, while the second extension was named “Solstice”, and lasted for six years and 205 days.

Cassini was the most complex planetary probe built to date

Cassini had many mission objectives, but the primary objectives are listed here:

• Determining the three-dimensional structure and dynamic behavior of the rings of Saturn
• Determining the composition of the satellite surfaces and the geological history of each object
• Determining the nature and origin of the dark material on Iapetus’s leading hemisphere
• Measuring the three-dimensional structure and dynamic behavior of the magnetosphere
• Studying the dynamic behavior of Saturn’s atmosphere at cloud level
• Studying the time variability of Titan’s clouds and hazes
• Characterizing Titan’s surface on a regional scale

To accomplish all of this, and more, the craft carried a full suite of instruments that included:

• Optical Remote Sensing (“Located on the remote sensing pallet”)
– Composite Infrared Spectrometer (CIRS)
– Imaging Science Subsystem (ISS)
– Ultraviolet Imaging Spectrograph (UVIS)
– Visible and Infrared Mapping Spectrometer (VIMS)

• Fields, Particles and Waves
– Cassini Plasma Spectrometer (CAPS)
– Cosmic Dust Analyzer (CDA)
– Ion and Neutral Mass Spectrometer (INMS)
– Magnetometer (MAG)
– Magnetospheric Imaging Instrument (MIMI)
– Radio and Plasma Wave Science (RPWS)

• Microwave Remote Sensing
– Radar
– Radio Science (RSS)

All told, Cassini’s instruments consisted of 1,630 electronic components, and 14 km (8.7 miles) of cabling/wiring to connect everything together with 22,000 wiring connections. The entire package was 6.8 meters (22 ft) long and 4 meters (13 ft) wide, and was propelled by one primary, and one back-up R-4D bipropellant rocket engine that each developed 490 newtons of thrust energy. Attitude control was provided by several smaller monopropellant rockets located at various points around the craft.

Cassini was also very expensive

By October 2000, Cassini had cost $3.26 billion, which figure included pre-launch development at $1.4 billion, $704 million for operating costs, $54 million for tracking services, and the launch vehicle that had a price tag of $422 million. Of the total budget, NASA contributed 80%, the European Space Agency contributed 15%, while the Italian Space Agency paid the remaining 5%. However, these figures represent only the costs up to October of the year 2000, and do not include the costs of the mission extensions, nor do they account for inflation over the entire life of the mission.

Cassini could have killed thousands of people

Due to Cassini’s huge power demands, it was fitted with a nuclear reactor that generated electrical power using 33 kilograms of plutonium-238. In addition, because the craft had to use Earth’s gravity to help propel it towards Saturn, there was a real possibility that if something went wrong and most of the plutonium was vaporized as the craft burned up in Earth’s atmosphere, the plutonium fuel could have caused up to 5,000 additional cancer deaths.

Titan by Huygens moduleAt the time of the Earth fly-by, it was estimated that up to five billion people would have been exposed to the deadly plutonium residue had something gone wrong, but at the same time, it was estimated that the chances of anything untoward happening was only about one in a million.

First picture taken on an outer-solar system moon

Cassini provided the ride for the Huygens module that was designed to land on Saturn’s moon Titan. Released from Cassini on December 25, 2005, the lander touched ground on Titan using parachutes to descend, and relayed data to the orbiting probe for about 90 minutes before failing. The image above is the first picture taken by Huygens of Titan’s surface, and while it took about 700 pictures in total, a software failure caused the loss of 350 of those images. Huygens also took pictures of several lakes of liquid hydrocarbons on its way to the surface, one of which near the moons’ North Pole is bigger than any of the Great Lakes in North America.

Cassini discovered seven new moons

The image below shows the discovery photograph of a previously unknown moon in the Keeler Gap, dubbed Daphnis. The wavy pattern in the edges of the Keeler Gap is a form of standing wave caused by the gravity of the moon on the dust particles on either side of the gap. Other moons discovered during the mission are:

Saturn Daphnis Waves• Methone, Pallene, and Polydeuces in 2004, although it was subsequently discovered that Voyager 2 had already imaged Pallene during its 1981 fly-by
• Daphnis in 2005
• Anthe in 2007
• Aegaeon (previously S/2008 S 1), in 2008
• S/2009 S 1 in 2009

Moreover, on April 15, 2013, Cassini also discovered what appears to be a new moon in the process of forming.

Cassini’s version of the Pale Blue Dot

The image below is part of a larger image named “The Day Earth Smiled”, and shows Earth as the bright blue dot under Saturn’s ring system. Although Cassini had taken similar “family” pictures of the Saturnian system before (in 2006 and 2012), the latest, this particular image was conceived by Carolyn Porco, the Cassini missions’ imaging team leader. At the time, Porco “…called for the people of the world to reflect on their place in the cosmos, to marvel at life on Earth, and, at the time the pictures were taken, to look up and smile in celebration.”

The Day Earth Smiled

The image was taken from a distance of 746 million miles from Earth, with the final, fully processed “The Day Earth Smiled” image released to the public on November 12, 2013.

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