Hints of an ocean hid­den on icy moon

Data from 1997 Galileo flyby of Jupiter of­fer hope

Sun Sentinel Palm Beach Edition - - NATION & WORLD - By Amina Khan Los Angeles Times

A space­craft wouldn’t know ev­i­dence of a Galilean lu­nar geyser if that geyser hit it in the face. Luck­ily, the sci­en­tists on the ground did.

Re­searchers us­ing 21year-old data from NASA’s Galileo space­craft have found ev­i­dence of a plume of ma­te­rial com­ing from the sur­face of Jupiter’s icy moon Europa. The dis­cov­ery of­fers a new line of ev­i­dence for an ocean be­neath its frozen crust and a promis­ing path for­ward in the search for ex­trater­res­trial life.

The re­sults show that old data from long-gone space­craft “hold a lot of se­crets we haven’t yet un­cov­ered,” said Lori Glaze, act­ing di­rec­tor of NASA’s Plan­e­tary Science Divi­sion.

If hu­mans are to look for life on other worlds, one of the first places sci­en­tists say they want to probe is cold, dis­tant Europa. One of the four large moons cir­cling our so­lar sys­tem’s big­gest planet, Europa’s frigid shell is thought to hide a global ocean that may hold twice as much wa­ter as Earth.

That ocean is kept “warm” (rel­a­tive to lo­cal stan­dards) and liq­uid thanks to en­ergy from enor­mous tidal forces, as the moon is squeezed and stretched largely by Jupiter’s grav­i­ta­tional pull. With enough heat and life-friendly chem­i­cals, such an ocean could po­ten­tially host the kinds of mi­crobes that are found in the depths of Earth’s oceans.

In 2012 NASA’s Hub­ble Space Te­le­scope spot­ted chem­i­cal hints of wa­ter mol­e­cules near the south­ern pole. If con­firmed, these icy gey­sers would pro­vide a sam­ple of the sub­sur­face ocean. But re­searchers de­bated whether the data re­vealed the pres­ence of such plumes.

A break­through came thanks to a pre­sen­ta­tion that Melissa McGrath of the SETI In­sti­tute gave about the lo­ca­tions of po­ten­tial plumes from Hub­ble images.

As he lis­tened to her talk, lead au­thor Xianzhe Jia, a space physi­cist at the Univer­sity of Michigan in Ann Ar­bor, came to a re­al­iza­tion: One of those pos­si­ble plume spots lay near a re­gion vis­ited by NASA’s Galileo space­craft, which ex­plored the Jo­vian sys­tem from 1995 to 2003. Per­haps ad­di­tional ev­i­dence of a plume was hid­den in the dead satel­lite’s decades-old data.

“That is the mo­ment that re­ally, I think, led us to re­al­ize that we had to go back to look at Galileo data,” Jia said.

The re­searchers looked at Galileo data from a De­cem­ber 1997 flyby, when the space­craft swooped to 124 miles above Europa’s sur­face.

The team found that as the space­craft made its close ap­proach to Europa’s sur­face, the mag­netic field went wild and the plasma den­sity shot up — an in­di­ca­tion that the space­craft was pass­ing through a plume.

“These re­sults pro­vide strong in­de­pen­dent ev­i­dence of the pres­ence of plumes at Europa,” the study au­thors wrote.

This dis­cov­ery could in­form plans for NASA’s Europa Clip­per mis­sion once it reaches the Jo­vian satel­lite, said El­iz­a­beth Tur­tle, a re­search sci­en­tist at Johns Hop­kins Ap­plied Physics Lab­o­ra­tory in Lau­rel, Md., who was not in­volved in the study.

“The hab­it­abil­ity of Europa is one of the big ques­tions that we want to un­der­stand,” Tur­tle said.

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