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Cassini’s plunge into Saturn after 20 years of planetary mission is a love story we must not forget

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Angshukanta Chakraborty
Angshukanta ChakrabortySep 15, 2017 | 15:45

Cassini’s plunge into Saturn after 20 years of planetary mission is a love story we must not forget

She’s not a rover. She’s a Saturn-circling, ring-grazing, moon-buzzing discovery machine. She’s a dazzler par excellence, on a mission for twenty long years, seven spent reaching the sixth planet of the Solar System, and 13 spent orbiting it in amazing elliptical paths. She’s Cassini, Saturn’s humanmade companion for half a Saturnian year, who inspected his many moons, picking a couple of them as possible repositories of rudimentary life, while moving at blazing speeds of 75,000 miles per hour through the planet’s rings.

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Cassini is dying today.

A spectacular example of humankind’s collective endeavour, and a work of art that strove for recording and transmitting unbelievable amount of data on the ringed planet and its moons, Cassini is plunging into the bosom of the very planet it was sent out to study. Back in 1997, it was Cassini-Huygens, and was launched on October 15 of that year.

By now, Cassini has spent 19 years and 11 months in space, six years and 261 days en route to Saturn, and 13 years 330 days orbiting this gas giant that revealed itself to this little, lovely, lonely warrior of hope and wisdom.

Hers was always a “cosmic fidayeen mission”, as I see it. Launched by NASA, European Space Agency (ESA) and Italian Space Agency, in cahoots with the Jet Propulsion Laboratory, Cassini-Huygens was a 5,712 kg probe, which had a number of gravity assists from inner planets, particularly Venus, and also the Earth-Moon combine, as well as Saturn’s immediate neighbour Jupiter, to finally reach the ringed planet in 2004.

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The spacecraft Huygens separated from Cassini in December 2004 and landed in Titan – Saturn’s biggest moon with methane lakes – in January 2005 to probe for signs of life. It was the first probe landing in a surface in the outer solar system.

This was a “postcard probe”, simply because of the beauty of the raw images that were sent out over the mission period. The processed images revealed unmatched and sublime Saturnian splendor, the 60 moons bathed in Saturnshine, sometimes even eclipsing the Sun.

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Cassini has revealed lakes and seas on Titan, Saturn's largest moon, filled with methane. Photo: Twitter

The photographs – composite and elaborate – are the products of Cassini endlessly acquiring shots of the giant planet and its moons – Titan, Enceladus, Mimas, Pandora, Dione, Rhea, Pan, Epimetheus, Anthe and more.

Before Cassini, there were Pioneer 11 (1979) and Voyager 1 (1980) and Voyager 2 (1981) sent out to study Saturn. The NASA Voyagers are now outside the Solar System, farthest probe ever. So yes, Cassini wasn’t the first NASA probe sent to study Saturn from a close range, but it sure has been the most spectacularly successful and durable one.

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To the extent that it has had two mission extensions – one in 2008 and another in 2010 – and then one last lap approved in the Grand Finale cosmic acrobatics that it has been doing since April this year, a set of 22 fly-bys, of six days each, the last one, nudged oh-slightly by Titan, would make Cassini plunge into the heart of Saturn, and embrace its fiery end.

 

September 15, at around 10-45 in the morning for NASA, Cassini will be the last in contact, sending the last tranche of invaluable images and data from Saturn’s inner rings, as well as from Saturn’s atmosphere before the latter overwhelms the feisty probe and perhaps makes it disintegrate. Scientists and Cassini enthusiasts say that if they start tweeting one unique image sent out by the probe every day, the treasure trove wouldn’t be over even at the end of our lives.

Hundreds of thousands of unique photographs, capturing Saturn from unbelievably beautiful angles, blocking out the Sun, catching the Sun, kissing Jupiter, winking at Earth from those many millions of miles away – all that and more has been Cassini’s amazing contribution in the history of cosmic probes. Let’s look at some of “major insights” provided by Cassini during its 13-year orbital one-probe-many-moons party in the Saturnian zone.

Saturn’s rings

Cassini has sent out most brilliantly detailed images of Saturn’s outer and inner rings, grading them painstakingly, helping catch the slightest disturbances in the patterns. Thousands of high-resolution images are now part of the Cassini treasure trove, with peeks into Saturn’s massive supra-planetary structures, and even the faint outer rings that were caught when Cassini captured a “backlit” Saturn with Sun on the other side.

Cassini captured “ring spikes” – even though the rings of Saturn are the “flattest structure known to man”, “ring waves or ripples” – caused by the passing of a moon like Dione.

Otherwise, the great flatness of the rings is demonstrated by the fact that the thickness varies only by 10 metres despite being stretched across hundreds of thousands of kilometres.

The insane storm

Up-close images from Cassini have revealed giant swirling storms going on for decades at end in Saturn’s north pole. Also known as the “hexagonal storm”, this is one of most impressive findings of Cassini. In fact, the storm came to light Cassini put itself in orbit around Saturn, and the north pole changed colours as season changed in Saturn.

The light illuminated a bizarre six-sided swirl of gases, and the polar hexagon is over 30,000 kilometres wide. The cloud speeds in the eye of the hexagon is over 150 metres per second, one of the fiercest known in the Solar System.

 

It must be remembered here that one Saturnian year is 29 Earth years. What Cassini saw on Saturn was the Earth equivalent of January to June, Spring and Summer on the ringed planet.

Brand new moons

Cassini discovered a number of unknown moons of Saturn, in addition to the big known ones like Titan, Enceladus and others. Some of the new moons discovered include Methone, Pallene, Polydeuces, Daphnis, Anthe and more.

Titan and Enceladus

Titan – Saturn’s largest moon – has been shown to have methane lakes in its northern hemisphere, a sign that life in its rudimentary form might have had a place in this amazing natural satellite of our sixth planet. Cassini has probed Titan’s terrain in its fly-bys across the moon, and Huygens probe too has been studying the moon since January 2005, when it landed into the surface of Titan with the help of a parachute!

In addition to lakes, Titan has methane seas, and Cassini’s radar probed its hydrocarbon-rich surface and atmosphere, indicating the prebiotic Earth-like setting. Could life evolve on Titan? Perhaps!

Enceladus, another moon of Saturn, is even more wonderful because under its thick icy surface – a moon-wide frozen ocean – lies a watery liquid ocean that’s warmer and jets from which shoot off into Enceladus’ atmosphere, creating brilliant water geysers that are the unique hallmark of this moon. Enceladus’ water jets are one of the most enchanting sights ever seen in the outer Solar System, making this moon one of the most promising candidate to hold life as we know it.

Saturn’s aurorae

Cassini spotted Saturn backlit, and then its shimmering aurorae in its south pole in July this year, during one of its Grand Finale laps around the planet, through its rings. The ghostly glow around Saturn’s south pole are because of sun striking the planet’s calmer gaseous atmosphere and charged particles hitting Cassini’s particle detector as it passes by.

Earth from Saturn

On July 19, 2013, Cassini saw something we Earthlings have never seen before, and wouldn’t for a pretty long time to come. Cassini saw Earth – the pale blue dot – as it passed by Saturn. The image is called “The Day The Earth Smiled”, and it made the frontpages of every worthwhile newspaper in this world, when it was released earlier this year.

That tiny dot was us, all of us, and our messenger, our cosmic ambassador was out there, encircling Saturn, the giant planet with its icy flat rings, and sending us a glimpse of our tiny abode in cosmic scale back to us. It was a humbling moment, as it was a moment of wonder. Cassini told us how little we are and how expansive is our thirst for knowledge, to the extent that even Saturn was welcoming of our stoic, persistent questioning across the ages. And here we are, toying with missile strikes, at each other’s throats. For what?

The Kamikaze end

In fact, why Cassini is ending its life in a blaze of glory and merging with its mission planet is precisely because of Saturn’s “potentially habitable moons”, Titan and Enceladus. Scientists do not want to compromise the pristine habitus of either Titan and Enceladus and “contaminate” the life forms there, if any, from an Earthling spore or two lurking somewhere in a nook of Cassini, despite millions spent on sterilisation.

If the probe was allowed to just have its flybys and hover in the Saturnian zone long after its fuel source was over – yes, nuclear fission from precious Plutonium – Cassini could have just smashed into two of the bigger Saturnian moons, pulled into orbit by their gravity. So no, Cassini will be crashing into Saturn itself, for no life exists in the gas giant, at least Cassini would be long immolated before it touches down, eaten up by Saturn’s crazily stormy, gaseous atmosphere.

Cassini has only a few hours left. The mission’s superlative Twitter handle @CassiniSaturn has done a marvelous job spreading the #Cassini love, telling its amazing story, the one that survived all odds, mission extensions, performed unimaginable cosmic acrobatics in space and over 200 orbits around the planet itself, innumerable around its moons, particularly Titan.

It’s Titan whose final “nudge” will be driving Cassini straight into Saturn’s stormy and heavy atmosphere, and the all the kindness and sublime beauty henceforth displayed by the gas giant will now turn into rage, rage against the transgression, and physics will ultimately trump over aesthetics and philosophy, eating up our great warrior Cassini.

Phil Plait, one of the most famous cosmic chroniclers and writers, says he’s choking up thinking only a few hours are left of Cassini’s life now.

So is Lisa Grossman, Emily Lakdawalla, and other science writers, who have followed Cassini from the time it was launched in 1997.

The veteran spacecraft will merge with the planet of its affection, and will enter the terrain of nostalgia, decorated with and remembered by memorabilia across the years, until, sometime in the future, a Cassini 2 starts off where its illustrious predecessor – our companion in the outer Solar System, in that cold, cold clime, had hung up its cosmic boots.

Goodbye Cassini. Rest in Saturn, your love in life, and in death.

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Last updated: September 15, 2017 | 17:29
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