Moon rocks brought by Apollo expeditions have been extensively researched to get information about both the Earth's satellite and the Sun's activity.

Because the Moon has no atmosphere or magnetic field, particles from the sun do not interfere with anything, penetrating and imbedding themselves into the lunar surface rocks since its existence, for almost four billion years. Studying the solar activity, researchers investigated in many Moon rocks the ratio of the isotopes of different solar gas elements, like neon isotopes (Ne20 and Ne22).

The light one (Ne20) has been regarded as solar wind, the other as higher-energy solar particles, because it was encountered at greater depths in the mineral grains. But Ne22 levels found in Moon rocks are much too large compared with current solar fluxes, pointing to very high solar activity in the past, issue that puzzled the scientists.

In order to investigate the problem, on NASA's Genesis mission, a bulk of specifically designed metallic glass was exposed to solar wind for 27 months. "We learned a great deal about the sun by going to the moon," said Don Burnett, Genesis lead 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."

This material, after the exposure in lab analysis, can be uniformly etched with nitric acid vapor allowing the measuring of the depth distribution of the solar wind neon isotopes. This analysis revealed isotopic variation immediately in shallow depths. The results were almost identical to those found in many lunar samples.

Genesis samples do not contain detectable levels of neon produced by solar ray particles, because in 27 months, there were no appreciable accumulations of such particles. Thus, they permitted the analysis of pure solar wind samples. The gas extractions from the metallic glass presented a different neon isotopic composition than that of the lunar samples.

Cosmic weathering and time erosion seem to have decreased the neon levels on the surface of the lunar samples and these samples lead to a misinterpretation. Ne22 isotope seem to be implanted deeper than the Ne20 isotope because of its larger weight and not energetic cargo.

These latest findings show no evidence for increased flows of high-energy solar particles in the past billion years.