Cassini's Great Space Adventure
Since the beginning of space exploration, several milestones have marked its history, each one enlarging our understanding of the cosmos and of our place in the Universe: the first man in space, the first man on the moon, the Apollo mission, the Voyager mission, the International Space Station, the rover in Mars - and now, the Cassini-Huygens mission.
Picture: NASA Named after two seventeen century scientists - Cristiaan Huygens and Jean Dominic Cassini, who were the firsts to study Saturn -, and after almost 15 years of previous preparation, the Cassini-Huygens mission was a gargantuan joint mission that fused the expertise of NASA, the European Space Agency (ESA), the Italian Space Agency, twenty-seven countries and more than 250 scientists worldwide.
Although Galileo Galilei had already made scientific notations on the planet back in the XVI century, he could not ascertain whether it was a single planet or a trio of planets.
It wasn’t until 1655 when, using the latest technology in telescopes available at the time, Cristiaan Huygens correctly declared that Saturn was a single planet surrounded by a ring. He also reported the existence of a moon, Titan.
Later, in 1671, Jean Dominic Cassini went further and declared that Saturn was surrounded by a series of rings (as opposed to only one), discovering four more moons in its orbit: Iapetus, Rhea, Tethys and Dione.
But why studying Saturn? What is it about this planet that’s so interesting to scientists?
Why Saturn?
Saturn is the second largest planet in our solar system, and its system of rings has always fascinated scientists.
However, data received from the Pioneer 11 in 1979, and later from the Voyager in 1980, discovered several intriguing and special aspects of Saturn that set it apart from the rest of the planets in our vicinity, particularly regarding its largest moon, Titan.
Unfortunately, the Voyager’s instruments weren’t strong enough to cut through the moon’s dense atmosphere to study it, leaving dozens of unanswered questions and the planting the crave to return for further investigation.
View of a sun eclipse from behind Saturn.
Photo: NASA/JPL-Caltech/SSI
Unlike the rest of planets in our solar system Saturn may be seen as a micro-cosmos in itself, with a host of moons orbiting around it.
Also, the wavy patterns in the rings resemble a miniature milky way, all of which could provide important clues to understand how planets form around stars. Moreover, a closer study of its rings could provide further information as to the age and origin of our solar system.
All of these seemed more than valid reasons to launch an investigative mission to this distant planet, but Cassini’s findings defied even the most ambitious scientific expectations.
What is Cassini?
Although small in size (4 mts in diameter and 6,8mts in height) and looking rather similar to Voyager, Cassini was a in fact a robotic spacecraft, with command capabilities far more complex than those of a simple probe.
Among several structural elements and software, Cassini carried 12 highly-specific instruments to collect a wide range of information about the Saturnian environment.
These allowed it to take images across the infrared, visible and ultraviolet spectra, detect and analyze dust particles and take diverse measurements.
These sophisticated instruments were like the eyes, nose, ears and skin of Cassini, allowing it to ‘feel’, as if to speak, the environment around it, as well as make precise calculations, and were divided into 3 sections:
1.- Optical Remote Sensing (the eyes of Cassini): Composite Infrared Spectrometer, Imaging Science Subsystem, Ultraviolet Imaging Spectrograph, Visible and Infrared Mapping Spectrometer.
2.- Fields, Particles and Waves (instruments that allowed to take diverse measurements of the atmosphere and capture valuable data of what can be found there.): Cassini Plasma Spectrometer, Cosmic Dust Analyzer, Ion and Neutral Mass Spectrometer, Magnetometer, Magnetospheric Imaging Instrument, Radio and Plasma wave science.
3.- Microwave Remote Sensing (instruments that helped to map atmospheres, determine the mass of the moons, collected data on ring particle size and unveiled the surface of Titan.): Radar, Radio Science Subsystem.
These instruments were fine enough to calculate measurements from a great distance, lowering thus the risk implied by direct contact.
However, Cassini also took direct sensing measurements and collected data straight from its surroundings, measuring magnetic fields, mass, electrical charges and densities of atomic particles, quantity and composition of dust particles, as well as the strengths of plasma, and radio waves in the environment.
Video: 1:06
What Was the Mission Like?
Cassini and the Huygens probe were launched on October 15th, 1997 from Cape Canaveral, Florida. After a seven-year journey, Cassini entered orbit around Saturn on June 30th, 2004 and immediately began to transmit data.
For navigation, it used stellar maps stored in its software, very much in the same manner navigators from ancient times.
Due to Titan’s thick atmosphere, scientist decided to send a probe (Huygens) to collect direct data from the moon, landing there on January 14th, 2005, and sending us the first images of the surface of this moon.
Huygens was the first man-made object ever to land on a moon in the solar system other than Earth’s.
Transmissions from Saturn take 83 minutes to reach Earth. Several groups of engineers were posted round the clock to collect all the data sent by Cassini and Huygens, translating it as fast as possible into usable information.
With these, scientists could decide where to send Cassini next, what needed to be explored further or where to move it in order to collect more data.
In fact, Cassini’s performance was so excellent that, after its 4-year primary mission, scientist decided to extend its tour twice in order to collect as much data as possible before its resources were exhausted.
However, while on Earth technology had advanced greatly in these past twenty years, Cassini was still stuck in the 1990's, as was the twin equipment on Earth to receive its communications.
In spite of this breach, the engineer teams worked wonders, collecting a trove of amazing data that slowly revealed the many wonders of the far planet.
Upper view of Saturn taken by Cassini
Photo: NASA/JPL-Caltech/SSI/Cornell
What Discoveries Did Cassini Make?
The massive amount of information sent by Cassini will still take decades to be analysed in full, but so far, its findings have updated our understanding of Saturn’s structure and its atmospheric make-up, including the realization that the planet has 62 moons, 20 more than originally thought.
Six of them were named in this mission: Metone, Palene, Pullox, Daphne, Anthe, Egeon.
Saturn’s orbit around the sun is 30 years long, and due to the length of this mission, Cassini was able to document the change of seasons in the planet and its moons during this period, which in turn may allow us a better understanding of the seasons on Earth as well as in other planets.
Infrared composite picture of Saturn's Southern hemisphere.
Photo: NASA/JPL-Caltech/ASI/University of Arizona
The thousands of majestic high-definition images taken by Cassini provide a level of detail of Saturn and its moons never achieved previously, yielding essential visual information to scientists, dissipating old intrigues, offering clues to new possibilities and arising new questions.
For instance, during its study of Saturn’s rings, Cassini revealed the existence of previously unseen, hidden moonlets amid them.
These cause waves on the surface of the rings, functioning as propellers and, due to their particular characteristics, may shed light on the formation of the solar system.
The Wonder of Saturn Video: 2:28
Cassini’s close measures of Saturn revealed that the planet’s magnetic field is different from any other planet we’ve known, shattering the Planetary Dynamo Theory which establishes that, in order to create the necessary motion for a magnetic field, a planet must have a certain tilt.
This information arises new possibilities that may change what we know about planetary physics.
The Huygens probe sent the first images from Titan, allowing us to see that it looks very much like Mars.
However, further explorations from Cassini (more than 1000 flybyes) revealed that this moon also has massive dunes, as well as rain, river-like channels and dozens of lakes.
In fact, Titan is the only celestial object in our solar system, aside from Earth, known to have liquid on its surface. Its weather, climate and geology provide new ways to understand our planet.
Six of Saturn's moons: Pan, Mimas, Hyperion, Iapetus, Titan and Enceladus.
Photo: NASA/JPL-Caltech/SSI
Thanks to Cassini’s close approach to Saturn, it could detect that the Enceladus moon is populated by geysers that spew jets of frozen sea water.
When testing its atmosphere, it discovered organic chemicals in it, as well as on its surface. This information would have been impossible to obtain without Cassini’s direct testing, and opens the door for the most exciting finding of them all: the possibility of alien life within our solar system.
It also observed Iapetus, solving a centuries-old questions regarding its surface: why this moon is always bright on one side and dark on the other.
As its neighbor moon, Phoebe (possibly an object from outer space, as also revealed in this mission), sheds its dark dust on Iapetus, it causes its ice surface to heat up and migrate to the moon’s opposite side.
Cassini also revealed that Hyperion’s sponge-like appearance is due to its low density and low gravity, and that the bright wisps on Dione’s surface, as captured by Voyager, were in fact canyons as those on Earth, also confirming the presence of oxygen ions around this moon.
In addition, it discovered that Prometeus creates streamers, plumes and drapes on Saturn’s rings through its interaction with them.
Why is all of this important?
A better understanding of the other planets in our solar system provides us with a better understanding of our own planet’s beginnings, allowing us to predict possible outcomes for life on Earth.
For example, much of what we know about Global Warming, its onset and effects, is thanks to data collected from observation of other planets in the solar system.
The Solar System
By reaching Titan and checking its conditions, scientists were allowed to learn that there are mountains, lakes, rivers of liquid and even an atmosphere, not unlike those of Earth in its early stages.
As far-fetched as it may sound today, this information opens the possibility of establishing a future colony on this moon or Enceladus.
Aside from the high quality images sent by Cassini, which provide unforeseen information about Saturn and its moons, its findings will still provide even more information about the formation of the planets and planetary systems, all of which will enlarge our knowledge of Earth and how to preserve life in it.
And What Now?
On September 15th, 2017, Cassini’s adventure came to an end, but not before yielding massive amount of data through a planned 6-month long ‘Grand Finale’.
Because of the high possibility that Titan and Enceladus could contain life (even in pre-biotic state), NASA scientists decided to have Cassini dissolve into Saturn’s atmosphere in order to avoid the possibility of contaminating these moons in the event of a crash.
The Grand Finale was conceived to reap the most from Cassini’s eventual and inevitable end.
The trajectory of Cassini's final dives.
Picture: NASA/JPL/Caltech/SSI
While several options were weighed, NASA scientists opted to induce Cassini into several dives past the outer and inner edges of the rings, ultra-close brushes with the planet and its small inner moons so as to obtain the maximum possible data from such a fantastic journey.
Twenty-two of such dives were successfully completed before its fuel reached to its near depletion.
As Cassini sent its final transmission to Earth and smashed against Saturn’s atmosphere, many an eye grew teary for its passing. But they also cheered in gratitude for the outstanding success of the ambitious mission, and the flawless execution of the spacecraft that surpassed all expectations and whose name will remain forever in history.
What Cassini found on Saturn made scientists rethink what they knew about the planet and the Solar System.
The mission is a triumph for human collaboration across divides, joined together in the most complex and ambitious unmanned expedition to outer space in history.
One likely to inspire generations of scientists, engineers and general public, and make them feel a little bit different when they look at the stars.
Did You Know...?
Cassini carried a DVD with over 600,000 signatures from people around the world. This was the first "Send your Name to" disk project by an aerospace agency. You can find the full story at http://saturn.jpl.nasa.gov/news/2803/dvd-with-signatures-on-way-to-Saturn
Want to Know More?
For more information, more photos and more videos, visit NASA’s and ESA’s official pages on Cassini:
Source: NASA, JPL, ESA, Wikipedia.
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