Solar wind particles solve lunar mystery - space - 16 November 2006 - New Scientist Space

"Trace chemicals ejected from the Sun and collected by NASA's Genesis
mission have solved a long-standing lunar mystery that threatened to
rewrite our understanding of how the Sun evolved.

For the last 4 billion years, energetic solar particles have bombarded
the Moon. But studies of these particles in rocks brought back by the
Apollo astronauts have mystified scientists.

That is because the ratio of two isotopes of neon have varied according
to depth in the rocks, with comparatively more neon-22 than neon-20 at
lower depths. That suggested that counter to theory, the Sun had once
been significantly more active than it is today, shooting out higher
energy particles that could travel farther into the rocks.

Now, Ansgar Grimberg at the Swiss Federal Institute of Technology (ETH)
in Zurich, and colleagues have resolved the conundrum."

More at http://space.newscientist.com/article.ns?id=dn10595