Saturn receiving water from one of its moons, ESA spacecraft finds | Science| In-depth reporting on science and technology | DW | 27.07.2011
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Saturn receiving water from one of its moons, ESA spacecraft finds

The planet's upper atmosphere is marked by the presence of water. But where it comes from has been a mystery until now. The ESA's Herschel spacecraft has identified water shooting from jets on Saturn's Enceladus moon.


Water sprays from Enceladus as it orbits Saturn

The European Space Agency's (ESA) Herschel spacecraft has identified the source of a water vapor ring surrounding Saturn. One of Saturn's moons - Enceladus - spews 250 kilograms (550 pounds) of water vapor into space every second. The announcement was published Tuesday on the ESA's website.

Anywhere from three to five percent of that water ends up falling onto the planet itself, influencing the chemical composition of its atmosphere. No other moon in the solar system is known to do so.

The water expelled from Enceladus mostly erupts from jets in an area of the moon's south pole known as the "Tiger Strips" for their distinctive markings.

Paul Hartogh, of the Lower Saxony-based Max Planck Institute for Solar System Research, led the analysis of data gathered by Herschel and told Deutsche Welle the water emitted by Enceladus is "enough to explain the amount of water first discovered in Saturn's atmosphere" in 1997.

Herschel spacecraft

The ESA spacecraft Herschel observed Saturn's moons

"The reason why so much water is produced is not clear," he said. "Of course you have this warm area in the south - and that is probably created by some tidal forces - but the exact mechanism is not know. The amount of energy dissipating due to tidal forces is actually not enough to explain why so much water is produced there."

Water for life

According to Tilman Spohn, of the German Aerospace Center's Institute of Planetary Research in Berlin, the discovery is a puzzling one which gives rise to more questions than it answers.

Enceladus' eruptions are surprising for a body of its size, he said. A general assumption is that the larger a body in space is, the more unstable and active it becomes.

"This thing is (actually) too small to generate volcanic activity and generate heat," Spohn told Deutsche Welle. "There is much more heat output than you would expect for a body like that."

Yet beyond Enceladus' inexplicable qualities, the moon has caught scientists' interest in part because the presence of liquid water is a prerequisite for life as we know it.

"There is speculation about Enceladus being habitable for microbial life forms - nobody has discovered anything like that yet, but it is a body of particular interest in terms of life outside the earth," Spohn said.

Compared with Earth

Walter Schmidt, a specialist on planets and comets at the Finnish Meteorological Institute of Helsinki, says Enceladus seems to be covered by an ice cap with water underneath.


Life as we know it - however small - requires liquid water

An early explanation for the eruption of water could be Saturn's gravitational pull on its moon, he said. Other moons of Saturn also have eruptions, although they spew materials other than water into space.

Because of the low pressure in space, the water coming from Enceladus becomes a vapor can't remain in its liquid form or freeze, which is why it becomes vapor, according to Schmidt. The water vapor is then broken down into hydrogen and oxygen by UV light and collisions with solar wind particles. That "basically ensures that water molecules are not stable in space," he added.

Schmidt says studying the conditions on Saturn and Enceladus can help scientists to "understand what makes Earth so special" in its ability to sustain life and explain "how water came here to Earth in the first place."

The spectroscopic capabilities of Herschel allow the spacecraft to distinguish between water, oxygen and hydrogen, Schmidt added.

"Water has a very characteristic spectral distribution and can be detected rather easily," he said. "Once it disassociates these spectral properties are gone, one has to look separately for oxygen lines and hydrogen lines."

Author: Gerhard Schneibel
Editor: Cyrus Farivar

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