Neon Lights up a Controversy: The Solar Ne/O Abundance

The standard solar model was so reliable that it could predict the existence of the massive neutrino. Helioseismology measurements were so precise that they could determine the depth of the convection zone. This agreement between theory and observation was the envy of all astrophysics—until recently, when sophisticated three-dimensional hydrodynamic calculations of the solar atmosphere reduced the metal content by a factor of almost 2. Antia & Basu suggested that a higher value of the solar neon abundance, ANe/AO = 0.52, would resolve this controversy. Drake & Testa presented evidence in favor of this idea from a sample of 21 Chandra stars with enhanced values of the neon abundance, ANe/AO = 0.41. In this Letter, we have analyzed solar active region spectra from the archive of the Flat Crystal Spectrometer on the Solar Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra from the pioneering days of X-ray astronomy in the 1960s. These data are consistent with the standard neon-to-oxygen abundance value, ANe/AO = 0.15 (Grevesse & Sauval). We conclude, therefore, that the enhanced-neon hypothesis will not resolve the current controversy.