Hydrogen emission from meteors and meteorites: mapping traces of H2O molecules and organic compounds in small Solar system bodies

The hydrogen emission from meteors is assumed to originate mainly from the meteoroid composition, making it a potential tracer of H2O molecules and organic compounds. H alpha line was previously detected in individual fireballs, but its variation in a larger meteor data set and dependence on the dynamical origin and physical properties have not yet been studied. Here, we investigate the relative intensity of H alpha within 304 meteor spectra observed by the AMOS (All-sky Meteor Orbit System) network. We demonstrate that H alpha emission is favoured in faster meteors (v(i) > > 30 km s(-1)) which form the high-temperature spectral component. H alpha was found to be a characteristic spectral feature of cometary meteoroids with similar to 92 per cent of all meteoroids with detected H alpha originating from Halley-type and long-period orbits. Our results suggest that hydrogen is being depleted from meteoroids with lower perihelion distances (q < 0.4 au). No asteroidal meteoroids with detected H emission were found. However, using spectral data from simulated ablation of different meteorite types, we show that H emission from asteroidal materials can occur, and apparently correlates with their water and organic matter content. Strongest H emission was detected from carbonaceous chondrites (CM and CV) and achondrites (ureilite and aubrite), while it was lacking in most ordinary chondrites. The detection of H alpha in asteroidal meteoroids could be used to identify meteoroids of carbonaceous or achondritic composition. Overall, our results suggest that H alpha emission correlates with the emission of other volatiles (Na and CN) and presents a suitable tracer of water and organic matter in meteoroids.