What has caused the secular increase in solar nitrogen-15?

Area of Science:

• * Planetary Science
• * Solar Physics
• * Geochemistry

Background:

• * Lunar surface samples exhibit variations in nitrogen isotope ratios.
• * These variations suggest changes in the solar wind composition over geological timescales.
• * The solar wind is the stream of charged particles released from the upper atmosphere of the Sun.

Purpose of the Study:

• * To investigate the cause of the observed variations in the nitrogen isotope ratio ((15)N/(14)N) in lunar samples.
• * To understand the implications of these variations for solar evolution.
• * To identify potential challenges to the current solar paradigm.

Main Methods:

• * Analysis of nitrogen isotope ratios ((15)N/(14)N) in lunar regolith and soil samples.
• * Comparison of isotopic data with models of solar wind evolution.
• * Examination of solar processes, specifically the solar convective zone.

Main Results:

• * A secular increase in the (15)N/(14)N ratio in the solar wind over the past few billion years is documented.
• * The source of this isotopic change appears to be linked to the solar convective zone.
• * The observed phenomenon is currently inexplicable within the framework of existing solar models.

Conclusions:

• * The variation in lunar nitrogen isotopes points to a significant, unexplained change in solar wind composition.
• * This finding presents a major challenge to our understanding of solar processes, comparable to the solar neutrino problem.
• * Further research into solar physics is required to reconcile these observations with current theories.