archive: SETI FW: Latest Lunar Prospector Findings Indicate Larger Amounts of Polar Water Ice

SETI FW: Latest Lunar Prospector Findings Indicate Larger Amounts of Polar Water Ice

Larry Klaes ( lklaes@zoomtel.com )
Thu, 3 Sep 1998 14:35:22 -0400

----------
From: NASANews@hq.nasa.gov
Sent: Thursday, September 03, 1998 2:21 PM
To: undisclosed-recipients:;
Subject: Latest Lunar Prospector Findings Indicate Larger Amounts of Polar Water Ice

Douglas Isbell
Headquarters, Washington, DC September 3, 1998
(Phone: 202/358-1753)

David Morse
Ames Research Center, Moffett Field, CA
(Phone: 650/604-4724)

RELEASE: 98-158

LATEST LUNAR PROSPECTOR FINDINGS
INDICATE LARGER AMOUNTS OF POLAR WATER ICE

The north and south poles of the Moon may contain up to
six billion metric tons of water ice, a more than ten-fold
increase over previous estimates, according to scientists
working with data from NASA's Lunar Prospector mission.

Growing evidence now suggests that water ice deposits of
relatively high concentration are trapped beneath the soil in
the permanently shadowed craters of both lunar polar regions.
The researchers believe that alternative explanations, such
as concentrations of hydrogen from the solar wind, are
unlikely.

Mission scientists also report the detection of strong,
localized magnetic fields; delineation of new mass
concentrations on the surface; and the mapping of the global
distribution of major rock types, key resources and trace
elements. In addition, there are strong suggestions that the
Moon has a small, iron-rich core. The new findings are
published in the Sept. 4 issue of Science magazine.

"The Apollo program gave us an excellent picture of the
Moon's basic structure and its regional composition, along
with some hints about its origin and evolution," said Dr.
Carl Pilcher, science director for Solar System exploration
in NASA's Office of Space Science, Washington, DC. "Lunar
Prospector is now expanding that knowledge into a global
perspective. The indications of water ice at the poles are
tantalizing and likely to spark spirited debate among lunar
scientists."

In March, mission scientists reported a water signal
with a minimum abundance of one percent by weight of water
ice in rocky lunar soil (regolith) corresponding to an
estimated total of 300 million metric tons of ice at the
Moon's poles. "We based those earlier, conscientiously
conservative estimates on graphs of neutron spectrometer
data, which showed distinctive dips over the lunar polar
regions," said Dr. Alan Binder of the Lunar Research
Institute, Gilroy, CA, the Lunar Prospector principal
investigator. "This indicated significant hydrogen
enrichment, a telltale signature of the presence of water
ice.

"Subsequent analysis, combined with improved lunar
models, shows conclusively that there is hydrogen at the
Moon's poles," Binder said. "Though other explanations are
possible, we interpret the data to mean that significant
quantities of water ice are located in permanently shadowed
craters in both lunar polar regions.

"The data do not tell us definitively the form of the
water ice," Binder added. "However, if the main source is
cometary impacts, as most scientists believe, our expectation
is that we have areas at both poles with layers of near-pure
water ice." In fact, the new analysis "indicates the
presence of discrete, confined, near-pure water ice deposits
buried beneath as much as 18 inches (40 centimeters) of dry
regolith, with the water signature being 15 percent stronger
at the Moon's north pole than at the south."

How much water do scientists believe they have found?
"It is difficult to develop a numerical estimate," said Dr.
William Feldman, co-investigator and spectrometer specialist
at the Department of Energy's Los Alamos National Laboratory,
NM. "However, we calculate that each polar region may
contain as much as three billion metric tons of water ice."

Feldman noted he had cautioned that earlier estimates
"could be off by a factor of ten," due to the inadequacy of
existing lunar models. The new estimate is well within
reason, he added, since it is still "one to two orders of
magnitude less than the amount of water predicted as possibly
delivered to, and retained on, the Moon by comets," according
to earlier projections by Dr. Jim Arnold of the University of
California at San Diego.

In other results, data from Lunar Prospector's gamma ray
spectrometer have been used to develop the first global maps
of the Moon's elemental composition. The maps delineate
large compositional variations of thorium, potassium and iron
over the lunar surface, providing insights into the Moon's
crust as it was formed. The distribution of thorium and
potassium on the Moon's near side supports the idea that some
portion of materials rich in these trace elements was
scattered over a large area as a result of ejection by
asteroid and comet impacts.

While its magnetic field is relatively weak and not
global in nature like those of most planets, the Moon does
contain magnetized rocks on its upper surface, according to
data from Lunar Prospector's magnetometer and electron
reflectometer. The resultant strong, local magnetic fields
create the two smallest known magnetospheres in the Solar
System.

"The Moon was previously interpreted as just an
unmagnetized body without a major effect on what is going on
in the solar wind," explained Dr. Mario Acuna, a member of
the team located at NASA's Goddard Space Flight Center,
Greenbelt, MD. "We are discovering that there is nothing
simple about the Moon as an obstacle to this continuous flow
of electrically charged gas from the Sun."

These mini-magnetospheres are located diametrically
opposite to large impact basins on the lunar surface, leading
scientists to conclude that the magnetic regions formed as
the result of these titanic impacts. One theory is that
these impacts produced a cloud of electrically charged gas
that expanded around the Moon in about five minutes,
compressing and amplifying the pre-existing, primitive
ambient magnetic field on the opposite side. This field was
then "frozen" into the surface crust and retained as the
Moon's then-molten core solidified and the global field
vanished.

Using data from Prospector's doppler gravity experiment,
scientists have developed the first precise gravity map of
the entire lunar surface. In the process, they have
discovered seven previously unknown mass concentrations,
lava-filled craters on the lunar surface known to cause
gravitational anomalies. Three are located on the Moon's
near side and four on its far side. This new, high-quality
information will help engineers determine the long-term,
altitude-related behavior of lunar-orbiting spacecraft, and
more accurately assess fuel needs for possible future Moon
missions.

Finally, Lunar Prospector data suggests that the Moon
has a small, iron-rich core approximately 186 miles (300
kilometers) in radius, which is toward the smaller end of the
range predicted by most current theories. "This theory seems
to best fit the available data and models, but it is not a
unique fit," cautioned Binder. "We will be able to say much
more about this when we get magnetic data related to core
size later in the mission." Ultimately, a precise figure for
the core size will help constrain models of how the Moon
originally formed.

Lunar Prospector was launched on Jan. 6, 1998, aboard a
Lockheed Martin Athena 2 solid-fuel rocket and entered lunar
orbit on Jan. 11. After a one-year primary mission orbiting
the Moon at a height of approximately 63 miles (100
kilometers), mission controllers plan to the lower the
spacecraft's orbit substantially to obtain detailed
measurements. The $63 million mission is managed by NASA's
Ames Research Center, Moffett Field, CA.

Further information about Lunar Prospector, its science
data return, and relevant charts and graphics can be found on
the project website at:

http://lunar.arc.nasa.gov

-end-

* * *

NASA press releases and other information are available automatically
by sending an Internet electronic mail message to domo@hq.nasa.gov.
In the body of the message (not the subject line) users should type
the words "subscribe press-release" (no quotes). The system will
reply with a confirmation via E-mail of each subscription. A second
automatic message will include additional information on the service.
NASA releases also are available via CompuServe using the command
GO NASA. To unsubscribe from this mailing list, address an E-mail
message to domo@hq.nasa.gov, leave the subject blank, and type only
"unsubscribe press-release" (no quotes) in the body of the message.