[meteorite-list] Genesis Findings Solve Apollo Lunar Soil Mystery

[Ron Baalke]

http://www.nasa.gov/mission_pages/genesis/media/Genesis_findings.html

Genesis Findings Solve Apollo Lunar Soil Mystery
November 20, 2006

Ever since astronauts returned from another world, scientists have been 
mystified by some of the moon rocks they brought back. Now one of the 
mysteries has been solved.

"We learned a great deal about the sun by going to the moon," said Don
Burnett, Genesis principal investigator at California Institute of
Technology, Pasadena, Calif. "Now, with our Genesis data, we are 
turning the tables, using the solar wind to better understand lunar 
processes."

Ansgar Grimberg from ETH Institute of Astronomy in Zurich and coworkers
analyzed the composition of neon in a metallic glass exposed on NASA's
Genesis mission. The team's findings are reported in a paper published
in the Nov. 17 issue of the journal Science. Burnett is a co-author of
the paper.

One of the stated goals of the Apollo missions was to understand the
history of the sun in time. With no atmosphere or magnetic field to
interfere, particles from the sun hit and imbedded themselves into the
lunar surface for almost four billion years. This goal was not fully met
due to the complexity of lunar materials and processes and to the
limited duration of the Apollo field operations.

Many of the lunar sample studies were of the relative amounts of the
isotopes of different solar gas elements. Many elements have atoms of
different mass. For example, neon has a light isotope (Ne20) and a heavy
isotope (Ne22).

One of the major surprises from study of the record of neon from the sun
in lunar soil samples was evidence for two solar gas components with
distinct isotopic compositions. One has been identified as solar wind,
the other as higher-energy solar energetic particles because it was
found at greater depths in the mineral grains. But the latter has long
been puzzling to scientists because its relative amounts were much too
large compared with present-day solar fluxes, suggesting very high solar
activity in the past.

To investigate this problem, a bulk metallic glass specially synthesized
by Charles Hays at NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
was exposed to the solar wind for 27 months on NASA's Genesis mission.
The advantage of this material is that when it is returned to Earth and
analyzed in a laboratory, it can be uniformly etched with nitric acid
vapor allowing the depth distribution of the solar wind neon to be
measured by stepwise release.

The first experiments at the ETH Institute in Zurich revealed surprising
results. Neon isotopic variations were not expected until relatively
large depths when the solar energetic particle regime would be reached,
but instead they were observed immediately. As etching proceeded, the
results were almost identical to those found in many lunar samples, with
two major differences.

First, Genesis samples do not contain detectable amounts of neon
produced by galactic cosmic ray particles because no appreciable
concentrations of such particles accumulated in 27 months. Thus they
allowed scientists to analyze pure solar wind samples.

Second, the first gas extractions from the bulk metallic glass showed
neon isotopic compositions never seen in lunar sample data. This finding
suggests that space weathering and erosion over time reduced the levels
of neon on the surface of all lunar samples, which in turn led to a
misinterpretation of the lunar data.

The researchers conclude that the Apollo solar energetic particles do
not exist. Both the Genesis and Apollo isotopic variations can be
quantitatively explained by the fact that the Ne22 isotope is implanted
deeper than the Ne20 isotope. Moreover, these findings indicate that
there is no evidence for enhanced fluxes of high-energy solar particles
billions of years ago compared to today.