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Vast underground glaciers reported on Mars

Nov. 20, 2008
Courtesy NASA
and World Science staff

NASA’s Mars Re­con­nais­sance Or­biter has de­tected vast glaciers of wa­ter ice un­der Mar­tian ground, re­search­ers say. The find­ings could pre­s­ent new av­enues for the search for life on Mars, they add, or pro­vide wa­ter to sup­port fu­ture hu­man ex­plora­t­ion.

Sci­en­tists an­a­lyzed da­ta from the space­craft’s ground-penetrating ra­dar and re­port in the Nov. 21 is­sue of the re­search jour­nal Sci­ence that bur­ied glaciers ex­tend for doz­ens of miles (kilo­me­ters) from the edges of moun­tains or cliffs. 

A lay­er of rocky de­bris blan­ket­ing the ice may have pre­served the un­der­ground glaciers as rem­nants from an ice sheet that cov­ered mid­dle lat­i­tudes dur­ing a past ice age, sci­en­tists said. This find­ing is si­m­i­lar to mas­sive ice glaciers that have been de­tected un­der rocky cov­er­ings in Ant­arc­ti­ca.

“Al­to­gether, these glaciers al­most cer­tainly repre­s­ent the larg­est res­er­voir of wa­ter ice on Mars that is not in the po­lar caps,” said John W. Holt of the Uni­ver­s­ity of Tex­as at Aus­tin, lead au­thor of the re­port. “Just one of the fea­tures we ex­am­ined is three times larg­er than the city of Los An­ge­les and up to half a mile thick.”

Sci­en­tists have puz­zled over what are known as apron­s—gently slop­ing ar­eas con­tain­ing rocky de­posits at the bas­es of taller geo­graph­i­cal fea­tures—since NASA’s Vi­king or­biters first ob­served them on the Mar­tian sur­face in the1970s. One the­o­ry has been that the aprons are flows of rocky de­bris lu­bri­cat­ed by a small amount ice. 

Now, the shal­low ra­dar in­stru­ment on the Mars Re­con­nais­sance Or­biter has of­fered “the smok­ing gun point­ing to the pres­ence of large amounts of wa­ter ice at these lat­i­tudes,” said Ali Safaeinili, a shal­low ra­dar in­stru­ments team mem­ber with NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Ca­lif.

Ra­dar ech­oes re­ceived by the space­craft in­di­cat­ed ra­dio waves pass through the aprons and re­flect off a deeper sur­face be­low with­out sig­nif­i­cant loss in strength, he ex­plained; that would be ex­pected if the apron ar­eas con­sisted of thick ice un­der a rel­a­tively thin co­vering. The ra­dar does­n’t de­tect re­flections from the in­te­ri­or of these de­posits as would oc­cur if they con­tained sig­nif­i­cant rock de­bris, he con­tin­ued. The ap­par­ent ve­locity of ra­dio waves pas­sing through the apron is con­sist­ent with a com­po­si­tion of wa­ter ice, he said.

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NASA’s Mars Reconnaissance Orbiter has detected vast Martian glaciers of water ice under protective blankets of rocky debris, researchers say. The findings could present new avenues for the search for life on Mars, they add, or provide water to support future human exploration. Scientists analyzed data from the spacecraft’s ground-penetrating radar and report in the Nov. 21 issue of the research journal Science that buried glaciers extend for dozens of miles (kilometers) from the edges of mountains or cliffs. A layer of rocky debris blanketing the ice may have preserved the underground glaciers as remnants from an ice sheet that covered middle latitudes during a past ice age, scientists said. This discovery is similar to massive ice glaciers that have been detected under rocky coverings in Antarctica. “Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that is not in the polar caps,” said John W. Holt of the University of Texas at Austin, lead author of the report. “Just one of the features we examined is three times larger than the city of Los Angeles and up to half a mile thick.” Scientists have puzzled over what are known as aprons—gently sloping areas containing rocky deposits at the bases of taller geographical features—since NASA’s Viking orbiters first observed them on the Martian surface in the1970s. One theory has been that the aprons are flows of rocky debris lubricated by a small amount ice. Now, the shallow radar instrument on the Mars Reconnaissance Orbiter has offered “the smoking gun pointing to the presence of large amounts of water ice at these latitudes,” said Ali Safaeinili, a shallow radar instruments team member with NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Radar echoes received by the spacecraft indicated radio waves pass through the aprons and reflect off a deeper surface below without significant loss in strength, he explained; that would be expected if the apron areas were composed of thick ice under a relatively thin covering. The radar doesn’t detect reflections from the interior of these deposits as would occur if they contained significant rock debris, he continued. The apparent velocity of radio waves passing through the apron is consistent with a composition of water ice, he said.