Saturn’s moon rains water onto Saturn

How cool would it be to stand on Enceladus and watch this....

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Water from Enceladus raining onto Saturn makes Enceladus the only moon in our solar system known to influence the chemical composition of its parent planet.

Once again proving that the universe is not only curiouser than we suppose, but curiouser than we can suppose, the European Space Agency (ESA) announced today (July 26, 2011) that water expelled from one of Saturn’s moons rains onto Saturn.

ESA’s Herschel space observatory – a large infrared space telescope, stationed at the second Lagrange point of the sun-Earth system – helped make the discovery. It found that water from Enceladus forms a giant torus of water vapor around Saturn.

Here’s what we already knew about water from Enceladus. In 2009, the Cassini spacecraft narrow-angle camera found at least four distinct plumes of water ice spewing out from the south polar region of Saturn’s moon Enceladus, as shown in the awesome image below.

Plumes of water shoot out of Enceladus: NASA

Image Credit: NASA/JPL/Space Science Institute

Cassini obtained this view of Enceladus in 2009 from a distance of approximately 617,000 kilometers (383,000 miles). In this image, light reflected off Saturn is illuminating the moon while the sun, almost directly behind Enceladus, is backlighting the plumes. This view looks toward the Saturn-facing side of Enceladus (504 kilometers across). North is up.

It’s been known for 14 years that there is water in Saturn’s upper atmosphere. ESA’s Infrared Space Observatory first reported in 1997 by teams using

Thanks to ESA’s Herschel space observatory, it’s now known that Enceladus expels around 250 kg of water vapour every second, through a collection of jets from the south polar region known as the Tiger Stripes because of their distinctive surface markings. Computer models of these latest Herschel observations show that the water creates a doughnut-shaped torus of vapor surrounding Saturn and about 3-5% of the water expelled by Enceladus ends up falling into Saturn.

The total width of the torus is more than 10 times the radius of Saturn, yet it is only about one Saturn-radius thick. Enceladus orbits the planet at a distance of about four Saturn radii, replenishing the torus with its jets of water.

Despite its enormous size, it has escaped detection until now because water vapor is transparent to visible light but not at the infrared wavelengths Herschel was designed to see.

Paul Hartogh, Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany, who led the collaboration on the analysis of these results, said:

There is no analogy to this behavior on Earth. No significant quantities of water enter our atmosphere from space. This is unique to Saturn.

He can say that again. Water from Enceladus ending up in Saturn’s atmosphere is truly bizarre and wonderful.

Although most of the water from Enceladus is lost into space, freezes on the rings or perhaps falls onto Saturn’s other moons, the small fraction that does fall into the planet is sufficient to explain the water observed in its upper atmosphere.

It is also responsible for the production of additional oxygen-bearing compounds, such as carbon dioxide.

Ultimately, water in Saturn’s upper atmosphere is transported to lower levels, where it will condense but the amounts are so tiny that the resulting clouds are not observable.

Bottom line: ESA’s Infrared Space Observatory found the water vapor in Saturn’s atmosphere in 1997. NASA/ESA’s Cassini/Huygens mission found the jets of Saturn’s moon Enceladus in 2009. Now, in 2011, ESA’s Herschel space observatory has been used to show that water from this moon of Saturn accounts for the water in Saturn’s upper atmosphere, making Enceladus the only moon in our solar system known to influence the chemical composition of its parent planet, and proving once again that nature … is cool.


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