by The Science and Technology
Facilities Council - UK
July 20, 2012
Scientists were able to
identify how small-scale magnetic "bubbles" were
efficient in deflecting the solar wind particles that
bombard the Moon.
The most striking "lunar swirl," known as Reiner Gamma,
can be seen from
Earth using a good telescope.
The Reiner Gamma
swirl is to the left of the image
near to the crater
Reiner after which it is named
Scientists from RAL Space at the Rutherford Appleton Laboratory in
the United Kingdom have solved a lunar mystery, and their results
might lead the way to determining if the same mechanism could be
artificially manipulated to create safe havens for future space
Their work focused on the origin of the
enigmatic "lunar swirls" - swirling patches of relatively pale lunar
soil, some measuring several tens of miles across, which have been
an unresolved mystery until now.
In the Apollo era, it was realized that lunar swirls were associated
with localized magnetic fields in the lunar crust - so-called lunar
Several unmanned spacecraft, like NASA’s
Lunar Prospector, JAXA’s
Kaguya, and India’s
Chandrayaan-1, have taken a special
interest in the regions of magnetic anomalies. Lunar Prospector
first identified magnetic anomalies that had created fully formed
but miniature "magnetospheres" similar to what Earth’s
planetary-wide magnetic field does on a much larger scale.
Using a combination of the space data and laboratory-scale
experiments that use a "solar wind tunnel," the team was able to
identify how such small-scale magnetic "bubbles" were more efficient
in deflecting the solar wind particles bombarding the Moon.
"When we first tried the experiment
in the solar wind tunnel and it worked, it was very exciting,"
said Ruth Bamford from the Center for Fundamental Physics and
RAL Space at the Rutherford Appleton Laboratory.
"The active force, which deflect the solar wind particles,
is electric, not magnetic. The
electric field is created naturally by the edges of the Moon's
magnetic ‘bubbles,’" Bamford said.
"What matters is the ‘gradient’ in
the magnetic field, rather than the overall size of the magnetic
bubble. So they can be as small as you like as long as the
gradient is steep enough."
Understanding how "mini-magnetospheres"
produce a cavity in the solar wind and exclude the interplanetary
magnetic field might lead the way to determining if the same
mechanism could be artificially manipulated to create safe havens
for future space explorers.
"We still need to determine quite
how effective this mechanism would be at deflecting the real
hazardous, higher-energy particles," Bamford said.
"The jury is still out on that one,
but such an active shield could make the difference between
survivable and certain death for astronauts on their way to
The lunar soil was originally white but
is known to have been darkened over time by exposure to the charged
particles of the solar wind.
It has long been thought that the swirls were a result of magnetic
shielding of the lunar surface from the solar wind, but nobody
understood how the relatively weak magnetic fields associated with
lunar swirls could sufficiently protect the Moon's surface over
hundreds of millions of years to prevent surface darkening and
produce such finely detailed patterns.
"Close to the Moon's surface, the
strength of a magnetic anomaly is likely to be very irregular,
featuring overlapping cavities and gradients.
We cannot know the
precise arrangement without going there to see for ourselves,"
but the result on the surface would be a corresponding pattern
of retarded and accelerated "space weathering," visible as areas
of lighter material separated by dark lanes.
Over an estimated 3.8 billion years,
these anomalies would have been deflecting the solar wind particles
streaming in from space, slowly creating these amazing patterns,
which can be clearly seen on the lunar surface today.
The idea was confirmed by experiments done in the laboratory with
the University of York in the United Kingdom using their "plasma
wind tunnel." The particles generated were, indeed, corralled by a
narrow electrostatic field, thereby protecting areas of the exposed
The interaction of the solar wind with the magnetic field anomalies
have been shown to be effective enough to create protected voids
above the surface of the Moon, sufficient to stave off against
weathering caused by the bombardment of solar particles.