15 September 2017

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Nasa Nine Ways Why Cassini-Huygens Mission Matters

Nasa Nine Ways Why Cassini-Huygens Mission Matters

The Cassini-Huygens mission—a joint endeavor of NASA, ESA (the European Space Agency), and the Italian Space Agency—is the first mission to orbit Saturn and explore its environs in detail.

The mission was conceived from the beginning as an international endeavor, in 1982, just after the two NASA Voyager spacecraft flew past Saturn.

The Voyager flybys whetted the appetites of planetary scientists for more in-depth exploration, particularly with regard to the mysterious moon Titan.

Launched in 1997, Cassini has been touring the Saturn system since arriving there in 2004, performing a detailed, up-close study of the planet, its rings and moons.

The mission delivered ESA's Huygens probe to Titan in 2005, where it performed the first descent and landing on a world in the outer solar system. In complement to Huygens' dazzling revelations about Titan, the Cassini orbiter performed 127 of its own close flybys of Titan (with many more distant encounters).

By the end of its mission, the Cassini spacecraft will have observed almost half of a Saturn year, which is 29 Earth years long.

The four seasons of Saturn's year last about seven Earth years apiece, and upon Cassini's arrival at Saturn, the planet's northern hemisphere was just beginning to emerge from winter. Following its initial, four-year tour, Cassini's mission was extended two more years, to enable the spacecraft to observe changes -- particularly in the rings -- as Saturn reached equinox and the Sun shone edge-on to the rings. After equinox, Cassini was granted an additional seven-year extension. This enabled scientist to follow up on their earlier discoveries at Enceladus and Titan, and watch as summer sunlight came to the northern hemisphere of Saturn and its moons, while winter darkness embraced the south.

Icy jets shoot from the tiny moon Enceladus. Titan’s hydrocarbon lakes and seas are dominated by liquid ethane and methane, and complex pre-biotic chemicals form in the atmosphere and rain to the surface. Three-dimensional structures tower above Saturn’s rings, and a giant Saturn storm circled the entire planet for most of a year. Cassini’s findings at Saturn have also fundamentally altered many of our concepts of how planets form around stars.

When Cassini ends, it will leave a rich scientific and engineering legacy.

Nine Ways Cassini-Huygens Matters –

1. NASA’s Cassini spacecraft and ESA’s Huygens probe expanded our understanding of the kinds of worlds where life might exist.
With discoveries at Saturn’s moons Enceladus and Titan, Cassini and Huygens made exploring “ocean worlds” a major focus of planetary science. Insights from the mission also help us look for potentially habitable planets -- and moons -- beyond our solar system.

2. At Saturn’s largest moon, Titan, Cassini and Huygens showed us one of the most Earth-like worlds we’ve ever encountered, with weather, climate and geology that provide new ways to understand our home planet.

3. Cassini is, in a sense, a time machine. It has given us a portal to see the physical processes that likely shaped the development of our solar system, as well as planetary systems around other stars.

4. The length of Cassini’s mission has enabled us to observe weather and seasonal changes, improving our understanding of similar processes at Earth, and potentially those at planets around other stars.

While other missions flew past Saturn or trained telescopes periodically from afar, Cassini has had a front-row seat for approximately 13 years -- nearly half a Saturn year (northern winter to the start of northern summer) -- to epic changes unfolding before its very eyes.

Among the most amazing changes Cassini captured: the eruption of a once-every-30-years storm (one of the most powerful ever seen in the solar system), methane rainstorms at Titan and the appearance and disappearance of features such as the “magic island.”

Over a longer span of years, the color of Saturn’s northern hemisphere shifted as the ring shadows retreated southward -- changing from the surprisingly bluish tones seen upon arrival to the hazy, golden hues most observers are familiar with. On Titan, Cassini witnessed a vortex filled with complex organic chemicals forming over its south pole, and saw sunlight glinting off of the lakes in its northern hemisphere as the sun rose over them.

The spacecraft’s patient eyes also were rewarded with new views of Saturn’s north pole as winter ended there and the sun rose once more. Cassini’s infrared sensors measured temperatures across the rings as the sun set on one side and rose on the other, revealing new details about the structure of ring particles. It used the onset of wintry darkness at the south pole of Enceladus to obtain an unambiguous reading of the amount of heat coming out of the moon’s interior. And it saw the mysterious ring features called spokes (wedge-shaped features in the rings that rotate along with the rings like the spokes in a wheel) appear and disappear -- apparently, a seasonal phenomenon.

5. Cassini revealed Saturn’s moons to be unique worlds with their own stories to tell.
The mission also followed up on a mystery from the early 1980s when NASA’s Voyager spacecraft flew by the Saturn system and saw bright wispy terrains on Dione. Cassini found that the features were in fact a vast network of canyons. Cassini also detected hints of a faint atmosphere that might have been outgassed from the moon’s interior.

6. Cassini showed us the complexity of Saturn’s rings and the dramatic processes operating within them.
When Galileo Galilei was observing Saturn in the 1600s, he noticed strange objects on each side of the planet. He drew in his notes a triple-bodied planet system with ears. These “ears” were later discovered to be the rings of Saturn.

7. Some of Cassini’s best discoveries were serendipitous. What Cassini found at Saturn prompted scientists to rethink their understanding of the solar system.

Towering jets of ice and water vapor pouring out of a moon as tiny as Enceladus were a huge surprise (explaining why Voyager flybys in the early 1980s saw that the moon had a young surface), as was the later finding that the moon has an ocean under its icy crust. Scientists also had not expected to find Saturn’s magnetosphere -- the region around the planet strongly influenced by Saturn’s magnetic field -- to be filled with an electrically excited gas, or plasma, of oxygen. It turned out this was another surprise from Enceladus, as the water vapor from its plume is broken apart by sunlight and the liberated oxygen spreads out through Saturn’s magnetic bubble. Cassini detected this oxygen on approach to Saturn, but its origin was perplexing at first.

No one knew for sure what kind of environment ESA’s Huygens probe would find when it came to rest on Titan’s surface, so Huygens was built either to land on hard ground or float, if need be. Cassini later showed scientists that most of the moon’s lakes and seas were near the north pole, and most of the moon’s landscape was more like the Arizona desert. Cassini also observed a surprisingly rich variety of complex, organic chemicals forming in Titan’s atmosphere.

8. Cassini represents a staggering achievement of human and technical complexity, finding innovative ways to use the spacecraft and its instruments, and paving the way for future missions to explore our solar system.

Over the course of almost 20 years in space, Cassini also showed that you can teach an old dog new tricks, as the mission team found new ways to use its instruments and engineering systems that their designers had not foreseen. These include using the radar instrument to plumb the depths of Titan’s seas; tasting the plume of Enceladus with instruments meant to sample Titan’s atmosphere; scanning the rings with a radar originally designed to bounce signals off of Titan’s surface; and having the Deep Space Network’s highly accurate frequency reference fill in for the radio science instrument’s lost ultra-stable onboard frequency reference. In a unique collaboration, the attitude control and navigation teams joined with the instrument teams to develop a consolidated model of Titan’s atmosphere. Cassini will finish its mission repurposing the instruments that sniffed Titan’s atmosphere and Enceladus’ plume once more, this time to sample the Saturn atmosphere itself.

9. Cassini revealed the beauty of Saturn, its rings and moons, inspiring our sense of wonder and enriching our sense of place in the cosmos.

Earthlings have cast their gaze upward at Saturn since ancient times, but it was Cassini’s decade-plus odyssey in orbit there that revealed the true splendor of what is arguably the most photogenic planet in our solar system.

The spacecraft also revealed the bewildering variety of Saturn’s moons and helped us see each one as a unique world in its own right. One has a noticeable ridge around its equator and a two-toned color pattern (Iapetus); one looks like the “Death Star” from Star Wars (Mimas); one looks like a sponge (Hyperion); another looks like a flying saucer (Atlas); another looks like a potato (Prometheus); another looks like a ravioli (Pan).

Source – NASA

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