[meteorite-list] Moon's Magnetic Umbrella Seen as Safe Haven for Explorers

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Nov 14 12:27:17 2006
Message-ID: <200611141727.JAA08213_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/061114_reiner_gamma.html

Moon's Magnetic Umbrella Seen as Safe Haven for Explorers
By David Powell
space.com
14 November 2006

The lunar surface is a harsh landscape; a bone dry expanse of impact-
pummelled rock whose "seas" have long been known as a misnomer. The
only precipitation is in the form of solar and cosmic radiation that
gradually darkens the dust and corrupts the cells of any astronauts
present.

Yet amidst this hostile landscape a number of safer havens exist where
the lunar surface escapes much of this sleet of radiation. One
such benign feature, named Reiner Gamma lies on the Moon's Earth
facing side and is marked by a 37-mile-long (60 km) bright swirl and
one of the strongest magnetic fields found on the lunar surface.

"The Moon presently has no global magnetic field similar to the Earth's.
The observed fields [such as that at Reiner Gamma] are caused by
permanent magnetization of parts of the lunar crust," said Lon Hood of
the University of Arizona.

Dramatic formation

These isolated pockets of lunar magnetism were discovered in the early
1970's by lunar-orbiting spacecraft and their formation is thought to be
as dramatic as their appearance.

"Current evidence suggests that impact-basin ejecta materials [material
blasted out by huge asteroid or comet are the most likely sources of
many or all of the magnetic fields," Hood said "These ejecta contain
microscopic metallic iron particles that are the carriers of the
magnetization."

This material became magnetized by the strong magnetic field present at
the time of impact and also from the magnetic fields generated during
other large, basin-forming impacts. Evidence for this is seen in the way
swirls present on the lunar far side lie directly opposite impact basins
on the Earth-facing side of the Moon.

The bright swirls of Reiner Gamma are a by-product of the contorted
magnetic field arching overhead, and there are currently two models for
the formation of the enigmatic swirls associated with the fields.

Two scenarios

The first hypothesis is that the swirls consist of secondary crater
ejecta whose bright deposits have been preserved by a strong local
crustal magnetic field.

One likely candidate for the bright ejecta preserved at Reiner Gamma is
that of the nearby three-billion-year-old crater Cavalerius. The
magnetic field present over Reiner Gamma would deflect the solar wind
and preserve the ejecta as a bright footprint of the magnetic field above.

The second mechanism for the swirls' formation is the relatively recent
impact of a comet nucleus. Such an event would create a feature similar
to Reiner Gamma and also magnetize the lunar surface.

>From the perspective of human explorers, Reiner Gamma boasts one of the
most scientifically interesting locations on the Moon.

"The main benefit would be to provide samples that are potentially free
from solar-wind ion bombardment," Hood said. "This would be useful for
understanding better the process that darkens the lunar surface and
other airless silicate surfaces in the inner solar system."

Not only does the magnetic field preserve an unsullied lunar surface but
it would partially protect any astronauts strolling beneath, "The lunar
fields are strong enough to deflect solar wind ions with energies of
several kilo-electron-volts," Hood said.

Fueling interest

Reiner Gamma's magnetic shield also channels the solar ions it does
divert into narrow regions surrounding the feature, another boon for
human exploration.

"This would concentrate solar wind hydrogen and helium-3 locally which
might be beneficial to increase the efficiency of mining these for
resource applications," Hood said. Helium-3 is a light isotope of
helium carried in the solar wind and is a potential fuel for
efficient and non-polluting nuclear fusion. The hydrogen would also be
essential to the manufacture of water for a lunar outpost.

Only a spacecraft on the surface will be able to definitively reveal the
method of Reiner Gamma's formation. Until then, future lunar orbiters
such as NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-1
spacecraft will undertake further analysis this unusual feature.
Received on Tue 14 Nov 2006 12:27:14 PM PST