the secrets of Saturn and its moons

NASA’s Cassini space probe has been one of the agency’s most successful missions ever. It has been collecting intelligence on Saturn for a decade now, giving astronomers amazing new insights while several times exceeding expectations for its overall lifespan. Perhaps more importantly, the probe has supplemented its scientific data with incredible optical photos that have captured the public imagination on more than one occasion; Cassini actually managed to squeeze some real enthusiasm from a jaded and desensitized population.
Now, though, its time has finally come. In 2016, after more than 11 years spent circling the famously ringed planet, Cassini will embark on its last mission ever. Now that we have a plan for the probe’s final days, it’s worth taking a look back at its incredible, decade-long history.
Cassini (actually called the Cassini-Huygens Probe) launched with a wide array of goals. NASA wanted to learn about the composition and flow of the rings, the chemical nature of the planet’s cloud cover, the geological history of its many moons, and even some detailed information about Titan. It had a long and ambitious list of projects when it arrived at Saturn on June 30, 2004, but that list turned out to be not nearly ambitious enough. From astrophysics to public relations, Cassini-Huygens has been a huge success for the space program.

Without a doubt, the most famous shot to come out of Cassini is the Saturnian solar eclipse. The probe spent 12 hours in the shadow of Saturn, collecting any and all sunlight streaming around or through the gas giant and its rings. The result was both inspiring and educational, as NASA actually discovered all-new rings that were too thin and dark to notice previously. Cassini also confirmed that Saturn’s so-called E Ring is actually made of ice crystals ejected from Enceladus — a moon with a super-cryo-volcano that was itself discovered by Cassini.
Actually, based on the characteristics of the E-Ring, astronomers had already been pretty certain of Enceladus as the source. Cassini’s flybys confirmed that the moon does in fact spew water and hydrocarbon ice out into space, where it quickly falls into orbit around Saturn. Not only did Cassini capture amazing images of these planet-scale cryo-eruptions, perhaps the most spectacular geological events ever captured, but later missions actually confirmed that they occur thanks to an enormous ocean of liquid water deep below the surface.

Enceladus and its iconic blue “tiger stripes.”

And then there’s Titan, the second of Saturn’s two celebrity moons. Titan is known for a variety of reasons, but it’s most interesting to astronomers because of its incredible size and odd surface conditions. Titan is actually larger (though less massive) than Mercury, the smallest planet in our solar system, and for a long time astronomers theorized that it could have large volumes of odd liquids sitting on its surface. Cassini confirmed it: the moon has huge lakes of natural gas — essentially jet fuel sitting right out on the surface of the moon.

Cassini was even the impetus for one of NASA’s most successful public outreach campaigns. If you look closely in the eclipse picture above you’ll see a small, almost unnoticeable dot on the left, just above the bright inner rings; that’s us. NASA got the idea of, for the first time ever, telling the public in advance of their decision to take a picture of the Earth. Called “The Day the Earth Smiled,” this campaign asked the public to look up and smile for the camera, creating the world’s largest group photo. It was all just symbolic of course, but it had the desired effect: for the next several weeks, people were once again talking about Saturn.

The final version of “The Day the Earth Smiled.”

That’s the interesting thing about Cassini, which has had such an odd and multifaceted career. Some of its insights have come as we predicted they would, others thanks to impromptu creativity on the part of astronomers; to detect the subterranean ocean we now know is inside Enceladus, scientists looked at tiny variations in the probe’s microwave carrier signal, which corresponds to tiny imperfections in Cassini’s orbit, which is a result of a non-standard internal distribution of mass. That Cassini has been so able to support these sorts of ideas is one major reason it’s been so successful overall.
The satellite’s Grand Finale, as democracy has named it, will be Cassini’s last hurrah — and it should be quite something. After another pass looking at the outer rings and at the ice-plumes from Enceladus, Cassini will begin “proximal orbits” in which it will pass between the planet and its inner-most ring. Such up-close data should be revolutionary to NASA’s understanding of Saturn’s weather and atmospheric composition. Not that this would be Cassini’s first amazing look into Saturnian cloud-science — the incredible Great White Spot was captured incredible detail.

Cassini has served mankind well, and after its Grand Finale mission it will retire to the planet that was its reason for existing. When Cassini spirals in to the center of that gas giants, sending back info for as long as it can, we will have concluded one of the most roundly successful missions in the agency’s history. Congratulations to the team.
source: http://www.extremetech.com