{"id":49418,"date":"2023-09-06T12:04:19","date_gmt":"2023-09-06T12:04:19","guid":{"rendered":"http:\/\/b723cf10-1639-4c8f-a914-b7d90d5edbf6"},"modified":"2023-09-06T12:33:06","modified_gmt":"2023-09-06T12:33:06","slug":"what-the-cassini-huygens-mission-discovered-at-saturn","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/what-the-cassini-huygens-mission-discovered-at-saturn\/","title":{"rendered":"What the Cassini-Huygens mission discovered at Saturn"},"content":{"rendered":"

A history of the Cassini-Huygens mission at Saturn and Titan. <\/p>

By Ben Evans\n <\/p>

Published: Wednesday, 06 September 2023 at 12:04 PM<\/p>

\n\n

The final moments of the Cassini mission’s 20-year voyage occurred on 15 September 2017, as the spacecraft sped towards its doom at 33.5km\/s.<\/p>

The bus-sized spacecraft passed briefly through Saturn<\/a>\u2019s brilliant, cobalt-blue skies, concluding one of the most spectacular scientific ventures in history.<\/p>

When Cassini plunged into the ringed planet\u2019s yellow-brown atmosphere, the seasonal blue sky was uncannily reminiscent of Earth\u2019s.<\/p>

A small reminder of the world where it was created.<\/p>

The Cassini\u2013Huygens mission (Huygens being the accompanying space probe that landed on Saturn’s moon Titan) was led by NASA, the European Space Agency, and the Italian Space Agency.<\/p>

But what was the Cassini mission, what did it do, and what were its biggest discoveries at Saturn?<\/p>

A view of Saturn captured by the Cassini spacecraft on 2 January 2010 from about 2.3 million km away. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Cassini’s journey to Saturn<\/strong><\/h2>
Cassini launched in October 1997 and travelled 3.5 billion km to reach Saturn, picking up gravitational boosts from Venus, Earth and Jupiter along the way.<\/p>
It arrived in July 2004, and released the tiny Huygens lander down to the surface of the giant moon Titan in December of the same year.<\/p>
Cassini went on to perform three extended phases of scientific study: in those 13 years it orbited the planet over 290 times, taking in Saturn\u2019s equinox and part of its northern summer solstice as it did so.<\/p>
$\"A$
A graphic showing the NASA Cassini mission’s path to Saturn. Credit: NASA<\/figcaption><\/figure>
NASA Cassini mission’s biggest discoveries<\/strong><\/h2>
The NASA Cassini mission found seven new moons at Saturn and explored dozens of others<\/p>
Their appearance ran the gamut from spherical to potato-shaped and from meatball-like to a kitchen sponge.<\/p>
Some planet-sized, others equivalent to the dimensions of a football stadium.<\/p>
More than a hundred flybys of Titan uncovered hydrocarbon rivers, lakes and seas, as well as a potentially habitable subsurface ocean.<\/p>
$\"Moon$
Moon Titan appears in front of Saturn in an image captured by NASA\u2019s Cassini spacecraft. Credit:\u00a0NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
\u201cMethane plays the role on Titan that water plays on Earth, carving river channels and filling Titan\u2019s lakes and seas, while a subsurface ocean resides beneath Titan\u2019s icy crust,\u201d says Cassini project scientist Linda Spilker.<\/p>
Cassini saw water-ice jets spurting from fissures at the south pole of the moon Enceladus<\/a>.<\/p>
These providea reservoir of material for Saturn\u2019s E ring and betraying the existence of a deep global ocean, with all of the ingredients necessary to host some form of life.<\/p>
Still other moons, including the Death Star-like Mimas, with its prominent crater, might also possess oceans.<\/p>
$\"Saturn's$
Saturn’s moon Mimas, as seen by the Cassini spacecraft. Credit: NASA<\/figcaption><\/figure>
Tenuous oxygen atmospheres, trillions of times thinner than our own, were found around Rhea and Dione.<\/p>
As for Saturn itself, the spacecraft witnessed a complex atmosphere on the cusp of seasonal change as the planet progressed along its 29-year orbit.<\/p>
Cassini occupied a ringside seat, observing exotic storms and jet streams, including the 30,000km-wide north polar hexagon<\/a>, whose winds peak at 320km\/h.<\/p>
It photographed violent lightning storms by day and night.<\/p>
It mapped the planet\u2019s magnetic field<\/a> and observed the evolution of an annually recurring white storm in the northern hemisphere.<\/p>
$\"Cassini's$
Cassini’s view of Saturn’s moon Dione. Credit: NASA<\/figcaption><\/figure>
Cassini’s ring discoveries<\/strong><\/h2>
Pioneer 11 and the two Voyager spacecraft observed Saturn\u2019s magnificent assemblage of water-ice rings more than three decades ago.<\/p>
But it was not until the arrival of the NASA Cassini mission that their nature was more precisely understood.<\/p>
Even as the spacecraft completed its Grand Finale<\/a> of 22 \u2018dives\u2019 between the innermost edge of Saturn’s rings<\/a> and the gas giant itself, it revealed astonishing new details.<\/p>
$\"NASA's$
NASA’s Cassini spacecraft captured these views of a propeller feature in Saturn’s A ring on 21 February 2017. Credit: NASA<\/figcaption><\/figure>
These included features likened to straw and propellers, on scales the size of the Earth\u2019s tallest buildings.<\/p>
The Voyagers observed strange radial \u2018spokes\u2019, up to 16,000km long.<\/p>
The spacecrafts\u2019 data on the spokes\u2019 formation and dissipation lifecycles implied that they were indeed small particles, suspended high above the plane of the rings by electrostatic charging.<\/p>
Cassini showed these spokes appeared and dissipated in a matter of hours.<\/p>
Data suggested that they might represent a seasonal phenomenon throughout Saturn\u2019s 29-year orbit, vanishing in midwinter and midsummer, and reappearing as the giant planet approaches the equinoxes.\u00a0<\/p>
$\"A$
A view of Saturn’s rings captured by the Cassini spacecraft. Credit: Source: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
With a breadth of 282,000 km, the rings extend the equivalent of three-quarters of the distance between Earth and the Moon<\/p>
And their dazzling reflectivity owes itself to the fact that they are composed of 99.9% water-ice, along with contaminants.<\/p>
Cassini\u2019s radar and visible observations \u2013 together with stellar occultations \u2013 have shown varying dimensions of ring particles, which extend from sand-like grains to mountain-sized boulders.<\/p>
**Cassini’s Enceladus discoveries<\/strong><\/h2>** $\"A$
A view of Saturn’s moon Enceladus captured by the Cassini spacecraft on 28 June 2007. In the background can be seen the shadows of Saturn\u2019s rings, cast on the planet\u2019s cloud tops. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Reflecting 95% of the sunlight that strikes it and brighter than a field of freshly fallen snow, Enceladus\u2019s youthful fa\u00e7ade was first observed by the twin Voyager spacecraft.<\/p>
That mission raised the possibilities of cryovolcanism<\/a> and perhaps the existence of a life-sustaining ocean beneath its frozen crust.<\/p>
A quarter of a century later, in 2005, the NASA Cassini mission turned its gaze to Enceladus and validated long-held theories that water-ice geysers in the polar region \u2013 gushing from deep fissures at hundreds of metres per second \u2013 were responsible for supplying many microscopic particles to Saturn\u2019s E ring.<\/p>
$\"An$
An image of Enceladus captured by Cassini, showing plumes of vapour bursting through Enceladus\u2019s icy crust. Credit: NASA\/JPL-Caltech\/SSI<\/figcaption><\/figure>
Later that year, Cassini passed directly through one of the plumes, revealing the presence not only of water vapour, but also volatiles such as nitrogen, methane and carbon dioxide.<\/p>
This enhanced the possibility that some form of hydrothermal activity could be at work deep within Enceladus.<\/p>
It strengthened theories that the tiny moon could harbour a salty subsurface ocean ripe for nurturing microbial life.<\/p>
$\"Tiger$
Tiger stripes on Enceladus, as seen by the Cassini spacecraft. Credit: NASA, ESA, JPL, SSI, Cassini Imaging Team<\/figcaption><\/figure>
Plumes of salty particles from so-called \u2018tiger-stripe\u2019 fissures at the south pole and gravitational field data from Cassini strongly inferred the existence of a salty ocean, perhaps up to 10km deep.\u00a0<\/p>
“Cassini\u2019s revolutionary findings at tiny Enceladus include a subsurface global, salty ocean containing organics, ammonia, hydrogen and silicates, with hydrothermal vents on its seafloor,” says Spilker.<\/p>
“These discoveries have fundamentally altered many of our concepts of where life may be found in our Solar System.”<\/p>
**Huygens probe’s landing on Titan<\/strong><\/h2>** $\"The$
The Huygens lander’s view of Saturn’s moon Titan, revealing its icy mountains. Credit: NASA\/ESA – ESA\/NASA\/JPL\/University of Arizona<\/figcaption><\/figure>
Deep beneath the murky orange clouds of Saturn\u2019s large moon Titan lies an Australia-sized plateau called Xanadu.<\/p>
Since 14 January 2005, it has been home to ESA\u2019s tiny Huygens probe.<\/p>
Until then, the very nature of Titan\u2019s surface \u2013 whether liquid or solid \u2013 was open to considerable debate. <\/p>
Huygens was designed to survive a landing on mountainous or flat terrain, and even in a lake or sea.<\/p>
The Huygens spacecraft separated from Cassini on Christmas Day 2004 and coasted for three weeks to its destination.<\/p>
$\"A$
A bowl of festive M&Ms in mission control during the release of the Cassini mission\u2019s Huygens probe onto the surface of Saturn\u2019s moon Titan. Credit: NASA\/JPL-Caltech<\/figcaption><\/figure>
Shortly before entering Titan\u2019s atmosphere, a wake-up timer brought its six instruments online. <\/p>
Descending via parachute, it was buffeted by vigorous eastward-blowing winds, diminishing to gentler gusts as it neared the surface.<\/p>
From an altitude of 15km, its images seemed to indicate an area of drainage channels.<\/p>
These perhaps lead to a liquid methane \u2018shoreline\u2019, together with tendrils of hydrocarbon ground-fog. <\/p>
However, Huygens landed on solid ground, kicking up a cloud of organic aerosols and leaving a 12cm indent.<\/p>
It bounced, slid, wobbled a few times, then came to a stop.<\/p>
$\"Views$
Views of Titan\u2019s surface as seen by the Huygens lander during its descent onto the surface of the icy moon, 14 January 2005. Credit: ESA\/NASA\/JPL\/University of Arizona<\/figcaption><\/figure>
For 90 minutes, the probe took a look at its gloomy environs, littered with hydrocarbon-coated water-ice pebbles, typically rounded and fist-sized.<\/p>
Early notions of a sticky, clay-like composition were later revised to be a sort of icy \u2018sand\u2019.<\/p>
Hauntingly, Huygens\u2019 on-board microphone provided the first audible sounds from another celestial body, recording the roaring of Titan\u2019s wind during descent before its batteries ran dead.<\/p>
How the Cassini mission ended<\/strong><\/h2>
$\"This$
This view of Saturn\u2019s atmosphere was captured by NASA’s Cassini spacecraft during its first Grand Finale dive past the planet on April 26, 2017.Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Several end-of-mission scenarios were considered, including a prohibitively long trek back to Jupiter, killing Cassini off through an impact with Saturn\u2019s rings or moons.<\/p>
Or entering a semi-stable graveyard orbit.<\/p>
For the aging spacecraft, none of them promised to be scientifically profitable.<\/p>
And as its fuel dwindled, another worry arose.<\/p>
The risk of a long-dead and out-of-control Cassini someday hitting and contaminating pristine Enceladus did not bear thinking about.<\/p>
A safe disposal was imperative.<\/p>
$\"A$
A 2006 observation of Saturn’s E ring by the Cassini spacecraft. The E ring is fed with icy particles via plumes erupting from the subsurface ocean of Saturn’s icy moon Enceladus. The moon’s shadow is seen as a dark dot within the ring. Credit: NASA\/JPL\/Space Science Institute<\/figcaption><\/figure>
Saturn\u2019s hydrogen-rich atmosphere provided that means of disposal, as well as offering the potential to gain new insights into the formation of the giant planets.<\/p>
Specifically, an enigmatic region of liquid metallic hydrogen, deep inside the gaseous planet, is thought to power Saturn\u2019s magnetic field.<\/p>
The result was the Grand Finale: a multi-month campaign that required the spacecraft to execute 22 death-defying \u2018ring dives<\/a>\u2019 between the planet and its rings from April to September 2017.<\/p>
On five of those dives, Cassini would actually enter the upper atmosphere, approaching within 1,700 km of Saturn\u2019s one-bar level, roughly equivalent to sea level pressure here on Earth.<\/p>
“This planned conclusion for Cassini\u2019s journey was far and away the preferred choice for the mission\u2019s scientists,” says Spilker.<\/p>
“Cassini would make some of its most extraordinary observations at the end of its long life.”<\/p>
Early in 2016, the spacecraft completed five manoeuvres to drastically reshape its orbit from an equatorial one into a higher inclination.<\/p>
$\"Saturn's$
Saturn’s north polar hexagon, as seen by the Cassini spacecraftCredit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Ring grazing<\/strong><\/h2>
In November 2016, as part of the NASA Cassini mission, series of 20 \u2018ring-grazing\u2019 orbits commenced.<\/p>
During these, Cassini hurtled within a thousand kilometres of the F ring \u2013 the outermost boundary of Saturn\u2019s dazzling necklace \u2013 every week for almost five months.<\/p>
At this distance, it could directly sample particles from the rings for the first time and resolved features as large as the tallest buildings on Earth.<\/p>
The ring grazing phase ended on 22 April as Cassini gained a gravitational tweak from Titan to establish conditions for the Grand Finale.<\/p>
Four days later, moving at 34.4km\/s, it made its initial dive through a gap between Saturn\u2019s cloud-tops and the inner edge of the innermost D ring.<\/p>
This positioned Cassini closer to the planet and its rings than ever before.\u00a0<\/p>
As a precautionary measure, its high-gain antenna was used to shield the delicate scientific instruments against particle impacts.<\/p>
But the region proved surprisingly dust-free.<\/p>
It was even nicknamed \u201cthe big empty\u201d by Cassini project manager Earl Maize.<\/p>
$\"Cassini$
Cassini took many images of Titan over its 13 year mission at Saturn. The mission ended on 15 September 2017, when it plunged into Saturn\u2019s atmosphere, but it\u2019s data is still providing scientific insight. Image Credit: NASA\/JPL-Caltech\/ASI<\/figcaption><\/figure>
Ring dives<\/strong><\/h2>
Over the following weeks, the spacecraft dived through the rings every 6.5 days.<\/p>
It imaged their radial extent at breathtaking resolution, measuring Saturn\u2019s gravitational and magnetic fields.<\/p>
And extensively mapping its northern and southern hemispheres.<\/p>
Rhythmically looping out to 1.3 million km from the planet, then sweeping inbound for another dive, the spacecraft\u2019s last five orbits from mid-August 2017 promised great drama, great risk and even greater reward.<\/p>
At this stage, Cassini was so close to Saturn that it would physically pass through its tenuous upper atmosphere.<\/p>
It sampled various species of molecular hydrogen and helium, examining small-scale structures and observing powerful polar aurorae and fast-moving vortices.<\/p>
As it completed its 292nd and final full orbit on 12 September 2017, Cassini performed a distant flyby of Titan.<\/p>
The moon\u2019s gravity offered a \u2018goodbye kiss\u2019, adjusting the spacecraft\u2019s course and causing it to plunge deep into Saturn\u2019s atmosphere.<\/p>
The final, partial orbit ended at 10:44 UT on 15 September, and Cassini began its descent just south of the equator, in the dead of the Saturnian winter.<\/p>
Cassini’s mission end<\/strong><\/h2>
$\"A$
A Cassini image showing Titan, Saturn\u2019s largest moon, behind the planet\u2019s rings. The smaller moon Epimetheus can be seen in the foreground. Image Credit: NASA\/JPL\/Space Science Institute<\/figcaption><\/figure>
Back on Earth, we knew nothing of the speccraft\u2019s end for over an hour.<\/p>
Travelling at the speed of light, across the 1.2 billion km gulf between Saturn and Earth, its final data reached the electronic ears of NASA\u2019s Deep Space Network at 12:07 UT.<\/p>
A bittersweet end to one of our longest space missions.<\/p>
Cassini vanished from existence and became part of the planet it had spent its life exploring<\/p>
We can modify a line from the famous poet Rupert Brooke, and be certain that some tiny corner of a foreign gas giant will remain forever Earth.<\/p>
***A version of this article originally appeared in the September 2017 issue of BBC Sky at Night Magazine.<\/em><\/strong><\/p> <\/body><\/html>\n***
","protected":false},"excerpt":{"rendered":"
A history of the Cassini-Huygens mission at Saturn and Titan. <\/p>\n","protected":false},"author":24,"featured_media":49419,"template":"","categories":[1],"acf":{"readingTimeMinutes":"12"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn.jpg",1200,800,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"A history of the Cassini-Huygens mission at Saturn and Titan.","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/49418"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/49419"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=49418"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=49418"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

A view of Saturn captured by the Cassini spacecraft on 2 January 2010 from about 2.3 million km away. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Cassini’s journey to Saturn<\/strong><\/h2>
Cassini launched in October 1997 and travelled 3.5 billion km to reach Saturn, picking up gravitational boosts from Venus, Earth and Jupiter along the way.<\/p>
It arrived in July 2004, and released the tiny Huygens lander down to the surface of the giant moon Titan in December of the same year.<\/p>
Cassini went on to perform three extended phases of scientific study: in those 13 years it orbited the planet over 290 times, taking in Saturn\u2019s equinox and part of its northern summer solstice as it did so.<\/p>
$\"A$
A graphic showing the NASA Cassini mission’s path to Saturn. Credit: NASA<\/figcaption><\/figure>
NASA Cassini mission’s biggest discoveries<\/strong><\/h2>
The NASA Cassini mission found seven new moons at Saturn and explored dozens of others<\/p>
Their appearance ran the gamut from spherical to potato-shaped and from meatball-like to a kitchen sponge.<\/p>
Some planet-sized, others equivalent to the dimensions of a football stadium.<\/p>
More than a hundred flybys of Titan uncovered hydrocarbon rivers, lakes and seas, as well as a potentially habitable subsurface ocean.<\/p>
$\"Moon$
Moon Titan appears in front of Saturn in an image captured by NASA\u2019s Cassini spacecraft. Credit:\u00a0NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
\u201cMethane plays the role on Titan that water plays on Earth, carving river channels and filling Titan\u2019s lakes and seas, while a subsurface ocean resides beneath Titan\u2019s icy crust,\u201d says Cassini project scientist Linda Spilker.<\/p>
Cassini saw water-ice jets spurting from fissures at the south pole of the moon Enceladus<\/a>.<\/p>
These providea reservoir of material for Saturn\u2019s E ring and betraying the existence of a deep global ocean, with all of the ingredients necessary to host some form of life.<\/p>
Still other moons, including the Death Star-like Mimas, with its prominent crater, might also possess oceans.<\/p>
$\"Saturn's$
Saturn’s moon Mimas, as seen by the Cassini spacecraft. Credit: NASA<\/figcaption><\/figure>
Tenuous oxygen atmospheres, trillions of times thinner than our own, were found around Rhea and Dione.<\/p>
As for Saturn itself, the spacecraft witnessed a complex atmosphere on the cusp of seasonal change as the planet progressed along its 29-year orbit.<\/p>
Cassini occupied a ringside seat, observing exotic storms and jet streams, including the 30,000km-wide north polar hexagon<\/a>, whose winds peak at 320km\/h.<\/p>
It photographed violent lightning storms by day and night.<\/p>
It mapped the planet\u2019s magnetic field<\/a> and observed the evolution of an annually recurring white storm in the northern hemisphere.<\/p>
$\"Cassini's$
Cassini’s view of Saturn’s moon Dione. Credit: NASA<\/figcaption><\/figure>
Cassini’s ring discoveries<\/strong><\/h2>
Pioneer 11 and the two Voyager spacecraft observed Saturn\u2019s magnificent assemblage of water-ice rings more than three decades ago.<\/p>
But it was not until the arrival of the NASA Cassini mission that their nature was more precisely understood.<\/p>
Even as the spacecraft completed its Grand Finale<\/a> of 22 \u2018dives\u2019 between the innermost edge of Saturn’s rings<\/a> and the gas giant itself, it revealed astonishing new details.<\/p>
$\"NASA's$
NASA’s Cassini spacecraft captured these views of a propeller feature in Saturn’s A ring on 21 February 2017. Credit: NASA<\/figcaption><\/figure>
These included features likened to straw and propellers, on scales the size of the Earth\u2019s tallest buildings.<\/p>
The Voyagers observed strange radial \u2018spokes\u2019, up to 16,000km long.<\/p>
The spacecrafts\u2019 data on the spokes\u2019 formation and dissipation lifecycles implied that they were indeed small particles, suspended high above the plane of the rings by electrostatic charging.<\/p>
Cassini showed these spokes appeared and dissipated in a matter of hours.<\/p>
Data suggested that they might represent a seasonal phenomenon throughout Saturn\u2019s 29-year orbit, vanishing in midwinter and midsummer, and reappearing as the giant planet approaches the equinoxes.\u00a0<\/p>
$\"A$
A view of Saturn’s rings captured by the Cassini spacecraft. Credit: Source: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
With a breadth of 282,000 km, the rings extend the equivalent of three-quarters of the distance between Earth and the Moon<\/p>
And their dazzling reflectivity owes itself to the fact that they are composed of 99.9% water-ice, along with contaminants.<\/p>
Cassini\u2019s radar and visible observations \u2013 together with stellar occultations \u2013 have shown varying dimensions of ring particles, which extend from sand-like grains to mountain-sized boulders.<\/p>
**Cassini’s Enceladus discoveries<\/strong><\/h2>** $\"A$
A view of Saturn’s moon Enceladus captured by the Cassini spacecraft on 28 June 2007. In the background can be seen the shadows of Saturn\u2019s rings, cast on the planet\u2019s cloud tops. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Reflecting 95% of the sunlight that strikes it and brighter than a field of freshly fallen snow, Enceladus\u2019s youthful fa\u00e7ade was first observed by the twin Voyager spacecraft.<\/p>
That mission raised the possibilities of cryovolcanism<\/a> and perhaps the existence of a life-sustaining ocean beneath its frozen crust.<\/p>
A quarter of a century later, in 2005, the NASA Cassini mission turned its gaze to Enceladus and validated long-held theories that water-ice geysers in the polar region \u2013 gushing from deep fissures at hundreds of metres per second \u2013 were responsible for supplying many microscopic particles to Saturn\u2019s E ring.<\/p>
$\"An$
An image of Enceladus captured by Cassini, showing plumes of vapour bursting through Enceladus\u2019s icy crust. Credit: NASA\/JPL-Caltech\/SSI<\/figcaption><\/figure>
Later that year, Cassini passed directly through one of the plumes, revealing the presence not only of water vapour, but also volatiles such as nitrogen, methane and carbon dioxide.<\/p>
This enhanced the possibility that some form of hydrothermal activity could be at work deep within Enceladus.<\/p>
It strengthened theories that the tiny moon could harbour a salty subsurface ocean ripe for nurturing microbial life.<\/p>
$\"Tiger$
Tiger stripes on Enceladus, as seen by the Cassini spacecraft. Credit: NASA, ESA, JPL, SSI, Cassini Imaging Team<\/figcaption><\/figure>
Plumes of salty particles from so-called \u2018tiger-stripe\u2019 fissures at the south pole and gravitational field data from Cassini strongly inferred the existence of a salty ocean, perhaps up to 10km deep.\u00a0<\/p>
“Cassini\u2019s revolutionary findings at tiny Enceladus include a subsurface global, salty ocean containing organics, ammonia, hydrogen and silicates, with hydrothermal vents on its seafloor,” says Spilker.<\/p>
“These discoveries have fundamentally altered many of our concepts of where life may be found in our Solar System.”<\/p>
**Huygens probe’s landing on Titan<\/strong><\/h2>** $\"The$
The Huygens lander’s view of Saturn’s moon Titan, revealing its icy mountains. Credit: NASA\/ESA – ESA\/NASA\/JPL\/University of Arizona<\/figcaption><\/figure>
Deep beneath the murky orange clouds of Saturn\u2019s large moon Titan lies an Australia-sized plateau called Xanadu.<\/p>
Since 14 January 2005, it has been home to ESA\u2019s tiny Huygens probe.<\/p>
Until then, the very nature of Titan\u2019s surface \u2013 whether liquid or solid \u2013 was open to considerable debate. <\/p>
Huygens was designed to survive a landing on mountainous or flat terrain, and even in a lake or sea.<\/p>
The Huygens spacecraft separated from Cassini on Christmas Day 2004 and coasted for three weeks to its destination.<\/p>
$\"A$
A bowl of festive M&Ms in mission control during the release of the Cassini mission\u2019s Huygens probe onto the surface of Saturn\u2019s moon Titan. Credit: NASA\/JPL-Caltech<\/figcaption><\/figure>
Shortly before entering Titan\u2019s atmosphere, a wake-up timer brought its six instruments online. <\/p>
Descending via parachute, it was buffeted by vigorous eastward-blowing winds, diminishing to gentler gusts as it neared the surface.<\/p>
From an altitude of 15km, its images seemed to indicate an area of drainage channels.<\/p>
These perhaps lead to a liquid methane \u2018shoreline\u2019, together with tendrils of hydrocarbon ground-fog. <\/p>
However, Huygens landed on solid ground, kicking up a cloud of organic aerosols and leaving a 12cm indent.<\/p>
It bounced, slid, wobbled a few times, then came to a stop.<\/p>
$\"Views$
Views of Titan\u2019s surface as seen by the Huygens lander during its descent onto the surface of the icy moon, 14 January 2005. Credit: ESA\/NASA\/JPL\/University of Arizona<\/figcaption><\/figure>
For 90 minutes, the probe took a look at its gloomy environs, littered with hydrocarbon-coated water-ice pebbles, typically rounded and fist-sized.<\/p>
Early notions of a sticky, clay-like composition were later revised to be a sort of icy \u2018sand\u2019.<\/p>
Hauntingly, Huygens\u2019 on-board microphone provided the first audible sounds from another celestial body, recording the roaring of Titan\u2019s wind during descent before its batteries ran dead.<\/p>
How the Cassini mission ended<\/strong><\/h2>
$\"This$
This view of Saturn\u2019s atmosphere was captured by NASA’s Cassini spacecraft during its first Grand Finale dive past the planet on April 26, 2017.Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Several end-of-mission scenarios were considered, including a prohibitively long trek back to Jupiter, killing Cassini off through an impact with Saturn\u2019s rings or moons.<\/p>
Or entering a semi-stable graveyard orbit.<\/p>
For the aging spacecraft, none of them promised to be scientifically profitable.<\/p>
And as its fuel dwindled, another worry arose.<\/p>
The risk of a long-dead and out-of-control Cassini someday hitting and contaminating pristine Enceladus did not bear thinking about.<\/p>
A safe disposal was imperative.<\/p>
$\"A$
A 2006 observation of Saturn’s E ring by the Cassini spacecraft. The E ring is fed with icy particles via plumes erupting from the subsurface ocean of Saturn’s icy moon Enceladus. The moon’s shadow is seen as a dark dot within the ring. Credit: NASA\/JPL\/Space Science Institute<\/figcaption><\/figure>
Saturn\u2019s hydrogen-rich atmosphere provided that means of disposal, as well as offering the potential to gain new insights into the formation of the giant planets.<\/p>
Specifically, an enigmatic region of liquid metallic hydrogen, deep inside the gaseous planet, is thought to power Saturn\u2019s magnetic field.<\/p>
The result was the Grand Finale: a multi-month campaign that required the spacecraft to execute 22 death-defying \u2018ring dives<\/a>\u2019 between the planet and its rings from April to September 2017.<\/p>
On five of those dives, Cassini would actually enter the upper atmosphere, approaching within 1,700 km of Saturn\u2019s one-bar level, roughly equivalent to sea level pressure here on Earth.<\/p>
“This planned conclusion for Cassini\u2019s journey was far and away the preferred choice for the mission\u2019s scientists,” says Spilker.<\/p>
“Cassini would make some of its most extraordinary observations at the end of its long life.”<\/p>
Early in 2016, the spacecraft completed five manoeuvres to drastically reshape its orbit from an equatorial one into a higher inclination.<\/p>
$\"Saturn's$
Saturn’s north polar hexagon, as seen by the Cassini spacecraftCredit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>
Ring grazing<\/strong><\/h2>
In November 2016, as part of the NASA Cassini mission, series of 20 \u2018ring-grazing\u2019 orbits commenced.<\/p>
During these, Cassini hurtled within a thousand kilometres of the F ring \u2013 the outermost boundary of Saturn\u2019s dazzling necklace \u2013 every week for almost five months.<\/p>
At this distance, it could directly sample particles from the rings for the first time and resolved features as large as the tallest buildings on Earth.<\/p>
The ring grazing phase ended on 22 April as Cassini gained a gravitational tweak from Titan to establish conditions for the Grand Finale.<\/p>
Four days later, moving at 34.4km\/s, it made its initial dive through a gap between Saturn\u2019s cloud-tops and the inner edge of the innermost D ring.<\/p>
This positioned Cassini closer to the planet and its rings than ever before.\u00a0<\/p>
As a precautionary measure, its high-gain antenna was used to shield the delicate scientific instruments against particle impacts.<\/p>
But the region proved surprisingly dust-free.<\/p>
It was even nicknamed \u201cthe big empty\u201d by Cassini project manager Earl Maize.<\/p>
$\"Cassini$
Cassini took many images of Titan over its 13 year mission at Saturn. The mission ended on 15 September 2017, when it plunged into Saturn\u2019s atmosphere, but it\u2019s data is still providing scientific insight. Image Credit: NASA\/JPL-Caltech\/ASI<\/figcaption><\/figure>
Ring dives<\/strong><\/h2>
Over the following weeks, the spacecraft dived through the rings every 6.5 days.<\/p>
It imaged their radial extent at breathtaking resolution, measuring Saturn\u2019s gravitational and magnetic fields.<\/p>
And extensively mapping its northern and southern hemispheres.<\/p>
Rhythmically looping out to 1.3 million km from the planet, then sweeping inbound for another dive, the spacecraft\u2019s last five orbits from mid-August 2017 promised great drama, great risk and even greater reward.<\/p>
At this stage, Cassini was so close to Saturn that it would physically pass through its tenuous upper atmosphere.<\/p>
It sampled various species of molecular hydrogen and helium, examining small-scale structures and observing powerful polar aurorae and fast-moving vortices.<\/p>
As it completed its 292nd and final full orbit on 12 September 2017, Cassini performed a distant flyby of Titan.<\/p>
The moon\u2019s gravity offered a \u2018goodbye kiss\u2019, adjusting the spacecraft\u2019s course and causing it to plunge deep into Saturn\u2019s atmosphere.<\/p>
The final, partial orbit ended at 10:44 UT on 15 September, and Cassini began its descent just south of the equator, in the dead of the Saturnian winter.<\/p>
Cassini’s mission end<\/strong><\/h2>
$\"A$
A Cassini image showing Titan, Saturn\u2019s largest moon, behind the planet\u2019s rings. The smaller moon Epimetheus can be seen in the foreground. Image Credit: NASA\/JPL\/Space Science Institute<\/figcaption><\/figure>
Back on Earth, we knew nothing of the speccraft\u2019s end for over an hour.<\/p>
Travelling at the speed of light, across the 1.2 billion km gulf between Saturn and Earth, its final data reached the electronic ears of NASA\u2019s Deep Space Network at 12:07 UT.<\/p>
A bittersweet end to one of our longest space missions.<\/p>
Cassini vanished from existence and became part of the planet it had spent its life exploring<\/p>
We can modify a line from the famous poet Rupert Brooke, and be certain that some tiny corner of a foreign gas giant will remain forever Earth.<\/p>
***A version of this article originally appeared in the September 2017 issue of BBC Sky at Night Magazine.<\/em><\/strong><\/p> <\/body><\/html>\n***
","protected":false},"excerpt":{"rendered":"
A history of the Cassini-Huygens mission at Saturn and Titan. <\/p>\n","protected":false},"author":24,"featured_media":49419,"template":"","categories":[1],"acf":{"readingTimeMinutes":"12"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2023\/09\/what-the-cassini-huygens-mission-discovered-at-saturn.jpg",1200,800,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"A history of the Cassini-Huygens mission at Saturn and Titan.","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/49418"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/49419"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=49418"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=49418"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}