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Scientists find out how moon makes own water: report

Oct. 16, 2009
Courtesy European Space Agency
and World Science staff

Moon, like a big sponge, ab­sorbs elec­tric­ally charged par­t­i­cles from the Sun, which in turn com­bine with ox­y­gen in some lu­nar dust to make wa­ter, sci­en­tists say.

They add that the find­ing—made us­ing the In­di­an Chan­dra­yaan-1 lu­nar or­biter—al­so sug­gests a new way to make im­ages of the Moon and oth­er air­less So­lar Sys­tem bod­ies.

Hy­dro­gen flow on the moon as meas­ured by the Chan­dra­yaan-1 lu­nar or­biter's Sub-keV At­om Re­flect­ing An­a­lyz­er. (Cour­tesy ESA) 


Re­search­ers re­ported only last month that the moon has ei­ther wa­ter or a si­m­i­lar mol­e­cule, called hy­drox­yl.

The lu­nar sur­face is a loose col­lec­tion of ir­reg­u­lar dust grains, called reg­o­lith. In­com­ing par­t­i­cles are probably trapped in the spaces be­tween the grains and ab­sorbed, ac­cord­ing to sci­en­tists.

When this hap­pens to pro­tons—elec­tric­ally charged par­t­i­cles that lie at the cores of at­om­s—the pro­tons are ex­pected to com­bine with the ox­y­gen in the reg­o­lith to pro­duce hy­drox­yl and wa­ter, the in­ves­ti­ga­tors ex­plain.

The re­search group, Stas Barabash of the Swed­ish In­sti­tute of Space Phys­ics and col­leagues, re­ported the find­ings in a pa­per to be pub­lished in the jour­nal Plan­e­tary and Space Sci­ence.

The re­sults con­firm that pro­tons are be­ing ab­sorbed by the reg­o­lith, but al­so high­light a mys­tery, Barabash said: not eve­ry pro­ton is ab­sorbed. One in five of them re­bounds in­to space and joins with an elec­tron, anoth­er sub­a­tom­ic par­t­i­cle, to be­come a hy­dro­gen at­om. “We did­n’t ex­pect to see this at al­l,” said Barabash, the Eu­ro­pe­an prin­ci­pal in­ves­ti­ga­tor for the or­biter’s Sub-keV At­om Re­flect­ing An­a­lyz­er, an in­stru­ment used in the re­search.

The dis­cov­ery paves the way for a new type of im­age to be made, he added. The hy­dro­gen shoots away with speeds about as fast as a speed­ing train and es­capes the moon. Hy­dro­gen is al­so elec­tric­ally neu­tral, and is not di­verted by the mag­net­ic fields in space, so the at­oms fly in straight lines, just like part­i­cles of light. 

In prin­ci­ple, each at­om can be traced back to its or­i­gin and an im­age of the sur­face can be made, Barabash pre­dicted. The ar­eas that emit most hy­dro­gen would ap­pear bright­est.


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Moon is a big sponge that absorbs electrically charged particles from the Sun, which in turn interact with the oxygen in some lunar dust to produce water, scientists say. They add that the finding—made using the Indian Chandrayaan-1 lunar orbiter—also suggests a new way to make images of the Moon and other airless Solar System bodies. Researchers reported only last month that the moon has either water or a similar molecule, called hydroxyl. The lunar surface is a loose collection of irregular dust grains, called regolith. Incoming particles are probably trapped in the spaces between the grains and absorbed, according to scientists. When this happens to protons—electrically charged particles that lie at the cores of atoms—the protons are expected to interact with the oxygen in the regolith to produce hydroxyl and water, the investigators explain. The research group, Stas Barabash of the Swedish Institute of Space Physics and colleagues, reported the findings in a paper to be published in the journal Planetary and Space Science. The results confirm that protons are being absorbed by the regolith, but also highlight a mystery, Barabash said: not every proton is absorbed. One in five of them rebounds into space and joins with an electron, another subatomic particle, to become a hydrogen atom. “We didn’t expect to see this at all,” said Barabash, the European principal investigator for the orbiter’s Sub-keV Atom Reflecting Analyzer, an instrument used in the research. The discovery paves the way for a new type of image to be made, he added. The hydrogen shoots off with speeds about as fast as a typical train and escapes the moon entirely. Hydrogen is also electrically neutral, and is not diverted by the magnetic fields in space, so the atoms fly in straight lines, just like photons of light. In principle, each atom can be traced back to its origin and an image of the surface can be made, Barabash predicted. The areas that emit most hydrogen would appear brightest.