Here are the top 10 things we wouldn’t know without Cassini.
  1. The Huygens probe makes first landing on a moon in the outer solar system (Titan)
  2. Discovery of active, icy plumes on the Saturnian moon Enceladus
  3. Saturn’s rings revealed as active and dynamic -- a laboratory for how planets form
  4. Titan revealed as Earth-like world with rain, rivers, lakes and seas
  5. Studies of the great northern storm of 2010-2011
  6. Radio-wave patterns shown not to be tied to Saturn’s interior rotation as previously thought
  7. Vertical structures in the rings imaged for the first time
  8. Study of prebiotic chemistry on Titan
  9. Mystery of the dual bright-dark surface of Iapetus solved
  10. First complete view of the north polar hexagon and discovery of giant hurricanes at both of Saturn’s poles

1. The Huygens probe makes first landing on a moon in the outer solar system (Titan)

First Color View of Titan's Surface
This image was returned Jan. 14, 2005, by the European Space Agency's Huygens probe after its successful descent to land on Titan. This colored view, following processing to add reflection spectra data, gives a better indication of the actual color of the surface.
Huygens's historic 2005 landing on Titan was the most distant in our solar system to date. The probe’s 2-hour and 27-minute descent revealed Titan to be remarkably like Earth before life evolved, with methane rain, erosion and drainage channels and dry lake beds. A soup of complex hydrocarbons, including benzene, was found in Titan's atmosphere. Huygens also provided the first on-site measurements of the atmospheric temperature.

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2. Discovery of active, icy plumes on the Saturnian moon Enceladus

The discovery of Enceladus's massive plume was such a surprise that mission designers completely reshaped the mission to get a better look. The discovery became even more important when Cassini found evidence of water-based ice in the plume. Life as we know it relies on water, so the search for life suddenly extended to this small, bright moon. The recent discovery of signs of an subsurface ocean makes Enceladus one of the most exciting science destinations in our solar system.

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3. Saturn’s rings revealed as active and dynamic -- a laboratory for how planets form

Commotion at Ring's Edge
The disturbance visible at the outer edge of Saturn's A ring in this image from NASA's Cassini spacecraft could be caused by an object replaying the birth process of icy moons.

Cassini’s decade-long mission made it possible to watch changes in Saturn’s dynamic ring system. The spacecraft discovered propeller-like formations, witnessed the possible birth of a new moon and observed what may be one of the most active, chaotic rings in our solar system (Saturn’s F ring).

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4. Titan revealed as Earth-like world with rain, rivers, lakes and seas

Titan's Northern Lakes (annotated)
Titan is the only place in the solar system other than Earth that we know has stable liquid on its surface, though its lakes are made of liquid ethane and methane rather than liquid water.

Imaging with radar, and both visible and infrared wavelengths shows that Titan has many geologic processes similar to that of the Earth. These processes generate methane rains, which build river channels and form lakes and seas containing liquid methane and ethane that don’t immediately evaporate.

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5. Studies of the great northern storm of 2010-2011

Storm Tail in False Color
These red, orange and green clouds (false color) in Saturn's northern hemisphere indicate the tail end of a massive storm that started in December 2010. Even after visible signs of the storm started to fade, infrared measurements continued to reveal powerful effects at work in Saturn's stratosphere.

Late in 2010, Saturn’s relatively tranquil atmosphere erupted with a storm of gigantic proportions. Typically a 30-year storm, this one arrived 10 years early, giving Cassini a front-row seat. Within months, this storm grew to encircle the planet with a swirling band. The largest temperature increases ever recorded for any planet were measured. Molecules never before seen in Saturn’s upper atmosphere were detected. The storm diminished shortly after its head collided with its tail, a little less than a year after it began.

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6. Radio-wave patterns shown not to be tied to Saturn’s interior rotation as previously thought

Saturn's Radio Period Crossover
This spectrogram and video show a changing pattern of radio waves from Saturn known as Saturn Kilometric Radiation, as detected by NASA's Cassini spacecraft. Recent data from the radio and plasma wave instrument show that the variation in radio waves controlled by the planet's rotation is different in the northern and southern hemispheres. 

Saturn emits radio waves known as Saturn Kilometric Radiation. A similar radio wave pattern was measured at Jupiter to deduce the length of that planet's day, but Saturn's daily rotation rate turned out to be much more complicated. Recent data from the radio and plasma wave instrument show that the variation in radio waves controlled by the planet's rotation is different in the northern and southern hemispheres. The northern and southern rotational variations also appear to change with the Saturnian seasons and the hemispheres have actually swapped rates. Saturn’s length of day is still not known.

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7. Vertical structures in the rings imaged for the first time

The Tallest Peaks
Vertical structures, among the tallest seen in Saturn's main rings, rise abruptly from the edge of Saturn's B ring to cast long shadows on the ring in this image taken by NASA's Cassini spacecraft two weeks before the planet's August 2009 equinox.

Once about every 15 years, the Sun shines on the edge of the ring plane and northern and southern sides of the rings receive little sunlight. Cassini measured the thick, long shadows from this rare event to determine the heights of structures within the rings.

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8. Study of prebiotic chemistry on Titan

Radar Shows Evidence of Seas
This movie, comprised of several detailed images taken by Cassini's radar instrument, shows bodies of liquid near Titan's north pole.

Titan’s atmosphere is a zoo teaming with a variety of molecules -- the most chemically complex in the solar system. Beginning with sunlight and methane, ever more complex molecules form until they become large enough to form the smog that covers the giant moon. Nearer the surface, methane, ethane, and other organics condense and fall to the surface where likely other prebiotic chemistry can take place.

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9. Mystery of the dual bright-dark surface of the moon Iapetus solved

Inky Stains on a Frozen Moon
Dark material splatters the walls and floors of craters in the surreal, frozen wastelands of Iapetus. This image shows terrain in the transition region between the moon's dark leading hemisphere and its bright trailing hemisphere. The view was acquired during Cassini's only close flyby of the two-toned Saturn moon.

The origin of Iapetus's two-faced surface has been a mystery for more than 300 years. The Cassini spacecraft solved the puzzle. Dark, reddish dust in Iapetus's orbital path is swept up and lands on the leading face of the moon. The dark areas absorb energy and become warmer, while uncontaminated areas remain cooler. The moon’s long rotation period contributes to the yin-yang effect.

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10. First complete view of the north polar hexagon and discovery of giant hurricanes at both of Saturn’s poles

Saturn's Streaming Hexagon
This colorful view from NASA's Cassini mission is the highest-resolution view of the unique six-sided jet stream at Saturn's north pole known as "the hexagon."

Saturn’s polar regions have surprised scientists with a the presence of a long-lived hexagonal-shaped jet stream in the north and two hurricane-like storms at both poles. The driving forces of each remain a mystery. In the remaining three years of Cassini’s mission, scientists hope to learn more of their properties and conditions surrounding their existence.

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