"Long before it's in the papers"
January 27, 2015


Water on Saturn found to be coming from its moon

July 26, 2011
Courtesy of the European Space Agency
and World Science staff

Cel­e­brat­ed for its beau­ty and awe-in­spir­ing rings, the plan­et Sat­urn now has a new dis­tinc­tion. Sci­en­tists say it’s the only plan­et we know whose own moon reg­u­lar­ly throws wa­ter—or any sub­stance—on­to it.

Wa­ter ex­pelled from the moon En­cel­a­dus forms a gi­ant do­nut-shaped ring of va­por around Sat­urn, which then leaks in­to the gi­ant plan­et’s at­mos­phere, re­search­ers claim. The finding would solve a 14-year mys­tery of where that wa­ter on Sat­urn came from.

Wa­ter plumes shoot from En­cel­a­dus. (Cred­its: NA­SA/JPL/Space Sci­ence In­sti­tute)

En­cel­a­dus spouts an es­ti­mat­ed 250 kg (550 lbs) of wa­ter va­por each sec­ond from a group of jets at a south po­lar re­gion, known as the Ti­ger Stripes for its dis­tinc­tive ap­pear­ance. The ejected wa­ter forms a do­nut that’s at least as wide as five Sat­urns, and about as thick as one-half a Sat­urn, re­search­ers say. Though enor­mous, the ring went un­no­ticed be­fore now be­cause see­ing it re­quires in­stru­ments that can de­tect in­fra­red light to see it.

The new re­search was done us­ing the Eu­ro­pe­an Space Agen­cy’s Her­schel space ob­serv­a­to­ry. Com­put­er mod­els based on its sight­ings show that about 3 to 5 per­cent of the wa­ter ex­pelled by En­cel­a­dus ends up fall­ing in­to Sat­urn, in­ves­ti­ga­tors said.

“There is no anal­o­gy to this be­hav­ior on Earth,” said Paul Har­togh of the Max Planck In­sti­tute for So­lar Sys­tem Re­search in Ger­ma­ny, who led the col­la­bora­t­ion on the anal­y­sis of the re­sults. “No sig­nif­i­cant quan­ti­ties of wa­ter en­ter our at­mos­phere from space. This is un­ique to Sat­urn.” 

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, he added. It’s al­so re­spon­si­ble for the pro­duc­tion of ad­di­tion­al oxygen-bearing com­pounds, such as car­bon di­ox­ide.

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

The find­ings are pub­lished in the Au­gust is­sue of the re­search jour­nal As­tron­o­my and As­t­ro­phys­ics.

* * *

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Celebrated for its beautiful rings, the planet Saturn now has a new distinction. Scientists say it’s the only planet we know whose own moon throws water—or any substance—onto it. Water expelled from the moon Enceladus forms a giant donut-shaped ring of vapor around Saturn, which then leaks into the giant planet’s atmosphere, researchers claim. Where that water came from was a 14-year mystery that is now solved, they add. Enceladus spouts an estimated 250 kg (550 lbs) of water vapor each second from a group of jets from a south polar region called the Tiger Stripes for its distinctive appearance. The ejected water forms a donut that’s at least as wide as five Saturns, and about as thick as one-half a Saturn, researchers say. Though enormous, the ring went unnoticed before now because seeing it requires instruments that can detect infrared light to see it. The new research was done using the European Space Agency’s Herschel space observatory. Computer models based on its sightings show that about 3 to 5% of the water expelled by Enceladus ends up falling into Saturn, investigators said. “There is no analogy to this behavior on Earth,” said Paul Hartogh of the Max Planck Institute for Solar System Research in Germany, who led the collaboration on the analysis of the results. “No significant quantities of water enter our atmosphere from space. This is unique to Saturn.” 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, he added. It’s 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, he added. The findings are published in the August issue of the research journal Astronomy and Astrophysics.