"Long before it's in the papers"
March 05, 2015

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Mars had an ocean, scientists say

March 5, 2015
Courtesy of W.M. Keck Observatory
and World Science staff

An ocean on Mars once held more wa­ter than Earth’s Arc­tic Ocean, ac­cord­ing to NASA sci­en­tists who meas­ured sig­na­tures of wa­ter in the plan­et’s at­mos­phere. 

The re­sults are be­ing pub­lished in the jour­nal Sci­ence on March 6.

The young Red Plan­et would have had enough wa­ter to cov­er the whole sur­face in a liq­uid lay­er about 450 feet (137 me­ters) deep, ac­cord­ing to re­search­ers. More like­ly, they say, the wa­ter would have cov­ered al­most half of Mars’ north­ern half, in some places reach­ing depths great­er than a mile (1.6 kilome­ters).

Reconstruction of how an ocean may have looked on early Mars. (Credit: NASA/GSFC)


“Our study pro­vides a sol­id es­ti­mate of how much wa­ter Mars once had, by de­ter­min­ing how much wa­ter was lost to space,” said Ge­ron­i­mo Vil­lanueva, an au­thor of the pa­per and sci­ent­ist at NASA’s God­dard Space Flight Cen­ter in Green­belt, Md.

The es­ti­mate is based on ob­serva­t­ions of two slightly dif­fer­ent forms of wa­ter in Mars’ at­mos­phere. One is the fa­mil­iar H2O, made with two hy­dro­gen at­oms and one ox­y­gen at­om. The oth­er is HDO, a nat­u­rally oc­cur­ring varia­t­ion in which one hy­dro­gen is re­placed by a heav­i­er form, called deu­ter­i­um.

The two forms are nat­u­rally found in pre­dict­a­ble ra­ti­os. Thus the in­ves­ti­ga­tors the­o­rize that if there is an ex­cess of HDO now, there must al­so have been more H20 in the past than there is now, and that this was lost.

The re­search­ers dis­tin­guished the chem­i­cal sig­na­tures of the two types of wa­ter from the W. M. Keck Ob­serv­a­to­ry in Ha­waii, NASA’s In­fra­red Tel­e­scope Facil­ity, al­so in Ha­waii, and from the Eu­ro­pe­an South­ern Ob­serv­a­to­ry’s Very Large Tel­e­scope in Chil­e. 

The team mapped H2O and HDO re­peat­edly over nearly six Earth years (a­bout three Mars years), pro­duc­ing glob­al snap­shots of each as well as their ra­tio. The maps re­veal sea­son­al changes and “mi­cro­cli­mates,” even though mod­ern Mars is es­sen­tially a des­ert, ac­cord­ing to the re­search­ers. These ra­tio maps are the first of their kind.

The team was es­pe­cially in­ter­est­ed in re­gions near the north and south poles, be­cause the po­lar ice caps are the plan­et’s larg­est known res­er­voir of wa­ter. The wa­ter stored there is thought to cap­ture the ev­o­lu­tion of Mars’ wa­ter from the wet No­a­chi­an pe­ri­od, which ended about 3.7 bil­lion years ago, to the pre­s­ent.

The new re­sults show that at­mos­pher­ic wa­ter in the near-po­lar re­gion was “en­riched” in HDO by a fac­tor of se­ven rel­a­tive to Earth’s ocean wa­ter, ac­cord­ing to the re­sults. That would imply that wa­ter in Mars’ per­ma­nent ice caps is en­riched by eight­fold. Mars must have lost a vol­ume of wa­ter 6.5 times larg­er than the pre­s­ent po­lar caps to pro­vide such large en­rich­ment, the sci­en­tists cal­cu­lat­ed.

By that meas­ure, they said, Mars’ early ocean must have held at least 20 mil­lion cu­bic kilome­ters worth of wa­ter. 

Based on the sur­face of Mars to­day, a likely loca­t­ion for this wa­ter would be in the North­ern Plains, which has long been con­sid­ered a good can­di­date be­cause of the low-lying ground, the study fur­ther pro­posed. An an­cient ocean there would have cov­ered 19 per­cent of the plan­et’s sur­face – by com­par­i­son, the At­lanti­c Ocean oc­cu­pies 17 per­cent of Earth’s sur­face.

“With Mars los­ing that much wa­ter, the plan­et was very likely wet for a long­er pe­ri­od of time than was pre­vi­ously thought, sug­gest­ing the plan­et might have been hab­it­a­ble for long­er,” said Mi­chael Mumma, a sen­ior sci­ent­ist at God­dard and co-au­thor on the pa­per.


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An ocean on Mars once held more water than Earth’s Arctic Ocean, according to NASA scientists who measured signatures of water in the planet’s atmosphere using Earth’s most powerful telescopes. The results are being published in the journal Science on March 6. The young Red Planet would have had enough water to cover the whole surface in a liquid layer about 450 feet (137 meters) deep, according to researchers. More likely, they say, the water would have covered almost half of Mars’ northern half, in some places reaching depths greater than a mile (1.6 kilometers). “Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, an author of the paper and scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The estimate is based on observations of two slightly different forms of water in Mars’ atmosphere. One is the familiar H2O, made with two hydrogen atoms and one oxygen atom. The other is HDO, a naturally occurring variation in which one hydrogen is replaced by a heavier form, called deuterium. The two forms are naturally found in predictable ratios. Thus the investigators theorize that if there is an excess of HDO now, there must also have been more H20 in the past than there is now, and that this was lost. The researchers distinguished the chemical signatures of the two types of water from the W. M. Keck Observatory in Hawaii, NASA’s Infrared Telescope Facility, also in Hawaii, and from the European Southern Observatory’s Very Large Telescope in Chile. The team mapped H2O and HDO repeatedly over nearly six Earth years (about three Mars years), producing global snapshots of each as well as their ratio. The maps reveal seasonal changes and “microclimates,” even though modern Mars is essentially a desert, according to the researchers. These ratio maps are the first of their kind. The team was especially interested in regions near the north and south poles, because the polar ice caps are the planet’s largest known reservoir of water. The water stored there is thought to capture the evolution of Mars’ water from the wet Noachian period, which ended about 3.7 billion years ago, to the present. The new results show that atmospheric water in the near-polar region was “enriched” in HDO by a factor of seven relative to Earth’s ocean water, according to the results. That would imply that water in Mars’ permanent ice caps is enriched by eightfold. Mars must have lost a volume of water 6.5 times larger than the present polar caps to provide such large enrichment, the scientists calculated. By that measure, Mars’ early ocean must have held at least 20 million cubic kilometers worth of water. Based on the surface of Mars today, a likely location for this water would be in the Northern Plains, which has long been considered a good candidate because of the low-lying ground, the study further proposed. An ancient ocean there would have covered 19% of the planet’s surface – by comparison, the Atlantic Ocean occupies 17% of Earth’s surface. “With Mars losing that much water, the planet was very likely wet for a longer period of time than was previously thought, suggesting the planet might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard and co-author on the paper.