Paris: Water on the Moon came in large
part from comets which bombarded the lunar surface in its
infancy, a study published today suggests.
For decades, the Moon was thought to have been as dry
as it was void of life and atmosphere.
This assumption, though, has been revisited after
findings by NASA last year of significant traces of frozen
water in a permanently shadowed crater.
Astrophysicists led by James Greenwood of Wesleyan
University in Connecticut analysed rock samples collected
during the Apollo expeditions, looking in particular at
variations in hydrogen isotopes in a water-loving mineral
The signature, they say, points to three potential
sources: from the sub-surface lunar mantle, from protons
brought by the "solar wind" of particles blasted from the Sun
-- and from comets.
The isotope measurements in the apatite were similar
to those previously found in three well-known comets:
Hale-Bopp, Hyakutake and Halley.
Comets have been described as frozen reservoirs of
water orbiting the Sun, for they contain vast quantities of
ice in their heads.
Under a "giant impact" theory dating back to the
1970s, the Moon was formed from part of Earth, after our
planet collided with a space rock or planet some 4.5 billion
"Significant delivery" of cometary water occurred
after the Moon-forming event, suggests Greenwood`s team.
Comets also provided Earth with some of its lavish
endowment of water as well as key chemicals to kickstart life,
according to some hypotheses.
The paper is published online by the journal Nature