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Saturn moon hides sea within, scientists conclude

April 3, 2014
Courtesy of Sapienza Uni­vers­ity of Rome
and World Science staff

A small moon of Sat­urn hides an un­der­ground body of wa­ter con­tain­ing about as much wa­ter as Lake Su­pe­ri­or, Earth’s sec­ond larg­est lake, as­tro­no­mers are re­port­ing.

The find­ings breathe new life in­to the pos­si­bil­ity that liv­ing things could in­hab­it the small, icy moon, En­cel­a­dus, they add.

Images of Enceladus showing "tiger stripes," cracks from which wa­ter spouts. (Cour­tesy NA­SA/JPL­/Space Sci­ence Ins­ti­tute)


Sci­en­tists reached their con­clu­sion by an­a­lyz­ing the gra­vity and sur­face shape of the moon as meas­ured by NASA’s Cas­si­ni space­craft. The re­search­ers, led by Lu­ciano Iess of the Sapienza Uni­vers­ity of Rome, are pub­lish­ing their find­ings in the April 4 is­sue of the jour­nal Sci­ence.

As­tro­no­mers at least three years ago said they had strong ev­i­dence that En­cel­a­dus had a sea un­der the sur­face. The clues came from the dis­cov­ery of wa­ter gey­sers rich in salts, emit­ted from long cracks in the sur­face. But the size and shape of any such res­er­voir were un­known.

The study pro­poses a sea ly­ing 30-40 km (a­bout 20-25 miles) be­neath the sur­face of the sat­el­lite’s south­ern po­lar re­gion, and ex­tend­ing to lat­i­tudes of per­haps 50 de­grees South. En­cel­a­dus it­self is about 500 km (310 miles) wide.

The in­ves­ti­ga­tors an­a­lyzed gravita­t­ional forc­es ex­erted by En­cel­a­dus on the Cas­si­ni craft dur­ing three fly­bys over the moon’s poles. “The very pre­cise mea­sure­ments tak­en by the Cas­si­ni probe made pos­si­ble by the large an­ten­nas of NASA’s Deep Space Net­work, show a neg­a­tive gravita­t­ional anomaly at the south pole that is how­ev­er not as large as ex­pected from the deep de­pres­sion de­tected by the on­board cam­era,” said Iess.

“Hence the con­clu­sion that there must be a dens­er ma­te­ri­al at depth that com­pen­sates the mis­sing mass: liq­uid wa­ter, in­deed, about 7 per­cent dens­er than ice.”

The sci­en­tists al­so be­lieve the wa­ter is in con­tact with a rocky floor below rath­er than with ice, mak­ing it more suit­a­ble for life. Con­tact be­tween wa­ter and sil­i­cates, min­er­al com­po­nents of rock, can fos­ter rich and com­plex chem­i­cal re­ac­tions that might be fa­vor­a­ble to the or­i­gin of life, giv­en an en­er­gy source, they added. Cas­si­ni’s in­stru­ments have de­tected or­gan­ic com­pounds both in dust grains emit­ted by the plumes and in the moon’s sur­face cracks, known as ti­ger stripes.


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A small moon of Saturn hides an underground body of water containing about as much water as Lake Superior, Earth’s second largest lake, astronomers are reporting. The findings breathe new life into the possibility that living things could inhabit the small, icy moon, Enceladus, they add. Scientists reached their conclusion by analyzing the gravity and ground structure of the satellite as measured by NASA’s Cassini spacecraft. The researchers, led by Luciano Iess of the Sapienza University of Rome, are publishing their findings in the April 4 issue of the journal Science. Astronomers at least three years ago said they had strong evidence that Enceladus had an ocean under the surface. The clues came from the discovery of water geysers rich in salts, emitted from long cracks in the surface. But the size and shape of any such reservoir were unknown. The study proposes an ocean lying 30-40 km (about 20-25 miles) beneath the surface of the satellite’s southern polar region, which may extend from the south pole to latitudes of about 50° South. Enceladus itself is about 500 km (310 miles) wide. The investigators analyzed gravitational forces exerted by Enceladus on the Cassini craft during three flybys over the moon’s poles. “The very precise measurements taken by the Cassini probe made possible by the large antennas of NASA’s Deep Space Network, show a negative gravitational anomaly at the south pole that is however not as large as expected from the deep depression detected by the onboard camera,” said Iess. “Hence the conclusion that there must be a denser material at depth that compensates the missing mass: liquid water, indeed, about 7% denser than ice.” The scientists also believe the water is in contact with a rocky floor rather than with ice, making it more suitable for life. Contact between water and silicates, mineral components of rock, can foster rich and complex chemical reactions that might be favorable to the origin of life, given an energy source, they added. Cassini’s instruments have detected organic compounds both in dust grains emitted by the plumes and in the moon’s surface cracks, known as tiger stripes.