t was an unusual applause. Everyone present in the big hall stood up and clapped together, but there was no hint of even a faint smile on any of the faces. The big twin monitors fixed on the wall, one above the other, were not showing any movement any more. The green flickering lines stood flat, lifeless. 'Cassini' was gone. The big clock on the wall kept ticking, announcing the passage of time as usual, indifferent to the flow of human emotions along its timeline. A tall lean man, in his fifties, stood up. Earl Maize, the programme manager of Jet Propulsion Laboratory, California, looked around, before speaking. There were almost a hundred people in that big room. Everyone wore one single colour- the purple, with pictures of Cassini on the dresses. Maize felt a prick of sharp pain in his heart. He was not sure if he could speak, as he felt a lump inside his throat growing from nowhere. After all, he was involved in all these for a long time, since 1992, dreaming the big dream and planning everything. Cassini was not even born then. She came to this world after five years. ‘1997 to 2017 –twenty long years’, he thought. Every scene of his life with Cassini around was passing one by one through his mind now, as in a movie they do. The mechanical tick of the wall clock brought Maize back to the present moment, cutting the flashback abruptly. He cleared his throat once and said, in a heavy yet firm voice, "I am going to call this the end of mission. Cassini has done an excellent job. And so did you, all of you. This ends our twenty year long Cassini-Huygens Saturn space mission. I thank you all"
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No one in the NASA team could think, on October 15, 1997, that it was going to be such a long story of twenty years, when 'Cassini Orbiter' lifted off gracefully that Wednesday, on her maiden voyage towards Saturn to explore the rings, moons and the mysterious magnetic field around the sixth planet of our solar system. She had another special piece of work, to explore Titan, the largest moon of the ringed planet, and for that she was carrying a small space probe, Huygens, with her, which she landed on Titan, later, with due care.
Information Box 1.1
Reaching Saturn was no easy job for Cassini, considering the 1.2 billion kilometers of space between Saturn and earth. There was a need for speed, her mentors had all agreed. When you escape earth’s gravity in a spaceship you start feeling the pull from the Sun, around which all the planets revolve. Your speed increases automatically in case your
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destination is one of the inner planets, the planets that come between earth and the Sun, as the Sun pulls you towards it; and it decreases if you are targeting any of the outer planets. Cassini was bound for Saturn, one of the outer planets.
There is a way known as Gravity assist or flyby, a technique to change speed and or direction or both of a spacecraft using little or no fuel. This can be achieved by flying close to a massive body in space. The scientists had planned three such flybys to give Cassini the right push and she executed all of them one after another and in 2004, she reached the neighbourhood of Saturn after seven years from the day she had taken off.
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Giovanni Domenico Cassini, the famous Italian astronomer, did a lot of work on Saturn. It was he who discovered four moons of the Saturn. They are Iapetus, Rhea, Tethys and Dione – all sound cute to the ears, one must agree. He also found a gap, known as Cassini division, in the rings around Saturn. Our little Cassini inherited the family name of this great scientist. Christiaan Huygens was a Dutch scientist and mathematician of the 17th century who not only developed a theory of the telescope but also used new ways to grind and polish the lenses to optimize his telescopes. Once he aimed one of his great telescopes at Saturn and could see Titan, the biggest moon of Saturn, for the first time in 1655. The who’s who of the
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planets and their moons, in our solar system, has it that Titan is second only to Jupiter’s moon, Ganymede, in size and it is bigger than even Mercury, the tiniest member in the group of planets circling around the Sun. It was no wonder that the sibling of Cassini, the small space probe that was accompanying her, was named after this great scientist who founded the wave theory of light as well. Cassini and Huygens together formed the Cassini-Huygens mission.
After a long journey of 6 years and 261 days, through dark and cold space, Cassini reached the neighbourhood of Saturn and started doing the assigned tasks there. Her mission, as had been decided initially, was to last for four years from her arrival in the kingdom of Saturn. It’s because of her good work that her term got extended two times - once for two years and then for six and a half again. She received orders, for these new missions, to study the ‘equinox’ and ‘solistice’, two simple geographical phenomena, known to Cassini and her mentors well, but Greek to most of the residents of the third planet in the solar system, who use the benefits of science and technology in their lives every minute, yet prefer to remain unaware about anything and everything of it. Cassini continued to obey all the commands that reached her from earth control like a good girl that she was.
Cassini has achieved something wonderful. She circled the planet about 300 times, discovered six new moons and a whole new class of moonlets. She also captured some excellent breathtaking pictures, about 4,50,000 in number. About 4000 research papers have already been published form the data she sent to earth.
We hadn’t known before Cassini visited there that the rings of Saturn are so active and dynamic. Cassini has made us to think that we must study the rings if we seriously want to know how planets and moons take birth.
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Cassini has brought in many surprises for mankind. She studied Enceladus, the sixth largest moon of Saturn, and found facts so astonishing that it might be a future hot spot for scientific exploration in search of life beyond earth. She also solved the mystery about why Saturn's moon Iapetus is black on one side and white on the other. Cassini studied in detail, the mysterious hexagonal cloud pattern around the north pole of Saturn. She also studied Titan, the biggest moon of Saturn, and collected amazing data from there. Above all, she has given us a huge number of excellent photographs of the Saturn system. All the text and images that we come across in text books meant for schools and colleges are a gift from Cassini. Cassini has sent back enough data to produce more than 1,400 scientific papers.
Information Box 1.2
Cassini found Enceladus hiding a global ocean of liquid water below its all ice white surface which provides a promising lead in our search for life beyond earth. Cassini also set the record of executing the first landing on a moon in the outer solar system when she dropped softly the Huygens space probe of the European Space Agency on the surface of Titan. Titan, Saturn’s largest moon, is revealed to have rain, rivers, lakes and seas all of liquid methane and ethane. Titan is shrouded in a thick, nitrogen rich atmosphere that might be similar to what Earth’s was like long ago.
Iapetus, the third largest moon of Saturn, was puzzling scientists for long, since the days of Giovanni Cassini. One side of this ice covered moon looks bright and the other side dark making it the strangest moon in the entire solar system. It’s as if Iapetus is moving through some dust or dirt which produces the "bugs on a windshield" effect. Thanks to Cassini, the 300 year old mystery of the moon Iapetus stands finally solved now.
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Voyager had discovered, in 1981, a persisting hexagonal cloud pattern around the north pole of Saturn, which contains a churning storm at its centre. Scientists have not found another weather feature exactly like this anywhere in the solar system. Cassini observed the hexagon changing, between 2012 and 2016, from a mostly blue color to more of a golden colour. The huge, mysterious hexagon at Saturn's North Pole may finally have an explanation with inputs from Cassini.
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Scientists normally do not agree on something too easily, but Saturn is mysterious – they would all agree, instantaneously. Saturn is the only planet in the Solar System whose rotation period is not yet known. Finding the rotation speed of solid planets, like the Earth and Mars, is simple for the planetary scientists. ‘Just measure the time it takes for a surface feature to roll into view again’, they would say. But giant gas planets like Jupiter and Saturn are a headache for them, as these planets both lack measureable solid surfaces and are covered by thick layers of clouds, preventing direct visual measurements by space probes. Saturn has presented an even greater challenge to scientists, as different parts of this sweltering ball of hydrogen and helium are known to rotate at different speeds. It is difficult for scientists to understand fully the internal structure of a planet without knowing the rotation period precisely.
The discovery made by Cassini that Enceladus may hide life in the ocean below its outermost ice cover led to the ‘death’ of Cassini, in an indirect way. Cassini was facing a big issue, the shortage of propellant fuel. She already overstayed there in the deep space for nine years, much beyond what was considered as normal when she took off twenty years ago. With its enormous rings and a family of about sixty moons at one count, Saturn presents a very complex gravitational field for any space probe to operate there. It would be impossible, with a dry fuel tank, to maneuver and control her so that she doesn’t collide with anything. The biggest problem was that what if she collided with Titan or Enceladus, where life might exist! As per international agreement on space exploration, no country is allowed to contaminate any planet or moon with micro organisms from earth. Cassini was disinfected before her journey but not up to the highest level. Besides, Cassini still had plutonium in her storeroom. Plutonium is a radioactive substance and harmful for living things. Frown lines on the foreheads of the NASA scientists were turning deeper now.
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Finally, it was decided, in April 2017, that Cassini should dive into the atmosphere of Saturn to finish her up and save Enceladus and Titan from contamination, in the process. On Sep 15, 2017, Cassini would make her final approach, it was planned, to the giant Saturn. Cassini was getting ready for her final mission, dubbed as the ‘Grand Finale’ by the NASA scientists. The task was to know more and more, as possible, before her ‘death’. Everything was planned by her mentors perfectly. She would go close to Titan for another gravity assist (visit page 2 for details) or flyby to change her orbit. The new orbit would take her to a territory not visited so far, the small gap between Saturn’s atmosphere and its rings. She would have to jump in this gap twenty two times and keep collecting scientific data. However, that path would lead her to an area where it would be impossible for her to avoid the big pull from the massive planet Saturn. She was now destined to fall and crash on Saturn. That didn’t matter – Cassini was on a death mission, she would have known, had she been a living
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being, like us. Was she scared, for a while? Impossible!! She was a machine only! On April 21 she started her final mission, the ‘Grand Finale’, with a close flyby of Titan, dubbed as the ‘goodbye kiss’. After executing all the dangerous dives, twenty two in number, in the narrow space between Saturn’s atmosphere and the rings and collecting invaluable data about the mysterious Saturn, she started falling towards the massive planet on Sep 15. Till her very end, she tried to focus her antenna towards earth. It had always been an easy job for her as she had done it a number of times before. Cassini knew very well how to stop tumbling using her thrusters, find the Sun with the solar detectors, center the antenna on the Sun, use her star-trackers to tweak its orientation to point at Earth, and radio home. But by this time, her computer was getting overheated due to friction with dense atmosphere of Saturn, causing it to fail. She ended her mission with a bright scatter of light as she now became a part of the planet she had studied for so long.
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The scientists at NASA were not ready to call this a ‘suicide’. ‘It’s a moment of pride’, they said. But is it too tough to understand, from how they behaved, what was going on in their minds on that day! They were hugging each other, wiping tears. Rarely, a day comes to our life, which presents us with an emotion never felt before, that we can’t make out which is more appropriate - tears or smile? Around 260 scientists from 17 countries had been working with Cassini. Was it their profession? Was it their passion? They had no answer. It’s a big vacuum that they would have to carry along till they live.
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Cassini was a machine, indeed, but she carried the quest of entire mankind to know the unknown, to see the unseen and to tell the untold. She represented all of us in that dark, cold, deep, unfriendly space where Saturn is and will be the king always. The combined consciousness of all of us on earth lit up the consciousness in her, Cassini never knew. In Cassini’s final moments she returned valuable data that would further unlock the mysteries of Saturn. We won’t say ‘RIP Cassini’. We say now what the scientists always wanted to, but could not - “Love you, Cassini! You have been the true daughter of mother earth! We are proud of you and we shall remember you always!”
Acknowledgements:
1. Source of all pictures (except at no. 2) and information presented: NASA, JPL, California, NASA has no connection, however, with the fiction and emotion presented to make the story more readable.
2. Telescope pic courtesy: http://giantsofscience.weebly.com/uploads/1/5/4/6/15469068/4495995.jpg
Further reading:
Read more about Cassini project and take a look at the amazing pictures at https://saturn.jpl.nasa.gov/
Nice citation
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