AFP/NASA/File – Water particles have been detected on the surface of
the Moon by three missions, including an Indian …
WASHINGTON – The moon isn't the dry dull place it seems. Traces of water lurk in the dirt unseen.
Three different space probes
found the chemical signature of water all over the moon's surface,
surprising the scientists who at first doubted the unexpected
measurement until it was confirmed independently and repeatedly.
It's not enough moisture to foster homegrown life on the moon. But if processed in mass quantities, it might provide resources — drinking water and rocket fuel — for future moon-dwellers, scientists say. The water comes and goes during the lunar day.
It's
not a lot of water. If you took a two-liter soda bottle of lunar dirt,
there would probably be a medicine dropperful of water in it, said University of Maryland astronomer
Jessica Sunshine, one of the scientists who discovered the water.
Another way to think of it is if you want a drink of water, it would
take a baseball diamond's worth of dirt, said team leader Carle Pieters
of Brown University.
"It's sort of just
sticking on the surface," Sunshine said. "We always think of the moon
as dead and this is sort of a dynamic process that's going on."
The
discovery, with three studies bring published in the journal Science on
Thursday and a NASA briefing, could refocus interest in the moon. The
appeal of the moon waned after astronauts visited 40 years ago and
called it "magnificent desolation."
The announcement comes two weeks before a NASA probe purposely smashes near the moon's south pole
to see if it can kick up buried ice. Over the last decade, astronomers
have found some signs of underground ice on the moon's poles. But this
latest discovery is quite different. It finds unexpected and pervasive
water clinging to the surface of soil, not absorbed into it.
"It is drier than any desert we have here," Sunshine said.
The
water was spotted by spacecraft that either circled the moon or flew
by. All three ships used the same type of instrument that looked at the
absorption of a specific wavelength of light that is the chemical
signature of only two molecules: water and hydroxyl. Hydroxyl is one
atom of hydrogen with one atom of oxygen, instead of two hydrogen atoms in water.
Because
of the timing during the daylight when some of that wavelength
disappears and some doesn't, it shows that both hydroxyl and water are
present, Sunshine said.
This light wavelength
was first discovered by an instrument on the Indian lunar satellite
Chandrayaan-1, which stopped operating last month. Scientists initially
figured something was wrong with the instrument because everyone knew
the moon did not have a drop of water on the surface, Pieters said.
"We
argued literally for months amongst ourselves to find out where the
problem was," Pieters said. Sunshine, who was on the team, had a
similar instrument on NASA's Deep Impact probe, headed for a comet but swinging by the moon in June. So Deep Impact looked for the water-hydroxyl signature — and found it.
Scientists
also looked back at the records of NASA's Cassini probe, which is
circling Saturn. It has the same type instrument and whizzed by the
moon ten years ago. Sure enough, it had found the same thing.
The
chance that three different instruments malfunctioned in the same way
on three different spaceships is almost zilch, so this confirms that
it's water and hydroxyl, Pieters said.
"There's just no question that it's there," Pieters said. "It's unequivocal."
Scientists
testing lunar samples returned to Earth by astronauts did find traces
of water, but they had figured it was contamination from moisture in
Earth air, Pieters said.
Three scientists who
were not part of the team of discoverers said the conclusion makes
sense, with Arizona State University's Ron Greeley using the same word
as Pieters: unequivocal.
Lunar and Planetary Institute senior scientist Paul Spudis called it exciting and said it raises the logical question: Where did that water come from?
Pieters figures there are three possibilities: It came from comets or
asteroids that crashed into the moon, those crashes freed up trapped
water from below the surface, or the solar wind carries hydrogen atoms that binds with oxygen in the dirt. That final possibility is the one that Sunshine and Pieters both prefer.
If it is the solar wind, that also means that other places without
atmosphere in our solar system, such as Mercury or asteroids, can also
have bits of water, Sunshine said.
___
On the Net
Science: http://www.sciencemag.org
NASA: http://www.nasa.gov
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