Lithium nucleosynthesis in the Sun inferred from the solar-wind 7Li/6Li ratio

The abundance of lithium measured in meteorites has generally been assumed to be the 'Solar System value', which presumably reflects the abundance in the gas cloud out. of which the Sun formed(1). Lithium is a factor of 140 less abundant in the solar photosphere than in meteorites(2); this difference has been attributed to the destruction of lithium (through nuclear reactions) at the base of the Sun's convection zone(3-5). If this is correct, then the ratio of Li-7/Li-6 in the Sun's photosphere should be similar to 10(6) (ref. 6), as Li-6 is destroyed much more easily (at a lower temperature) than Li-7: the meteoritic abundance ratio is Li-7/Li-6 = 12.14 (ref. 7). Here we report that Li-7/Li-6 = 31 +/- 4 for lithium in the solar wind that has been implanted in lunar soil. This low Patio suggests that lithium is produced when energetic protons from solar flares induce spallation reactions with O-16 and C-12 present in the photosphere.