The properties of cm–sized iron meteoroids

Abstract We collected meteors with iron spectra observed by the newly developed Spectral Digital Autonomous Fireball Observatories (SDAFO). SDAFOs are run within the European Fireball Network and extend the spectral observation of this network. Iron meteoroids can be distinguished using their spectra by the absence of lines of Na, Mg, Cr, Ca, and other usually bright lines of meteoritic origin. Among 220 fireball spectra that were observed by SDAFOs in 2015–2019 and that showed at least three spectral lines, eight were meteors with iron spectra. We added to the collection one additional iron meteor, which was observed with Digital Autonomous Observatories (DAFO: non–spectral cameras), the iron spectrum of which was observed with the spectral cameras of the AMOS Network (Matlovic et al., 2019). We present atmospheric trajectories, light curves, and heliocentric orbits of these iron fireballs. The orbits are asteroidal, or Sun approaching, and show diversity similar to those of mm–sized iron meteoroids. The inclinations vary from nearly zero up to ≈ 70 ∘ . The maximum brightness of all fireballs was between magnitude −6 and −10, corresponding to meteoroid diameters about 1–4 cm. Seven fireballs were classified as type IIIA, and two fireballs were classified as type IIIB in the classification of Ceplecha and McCrosky (1976), pointing out, at least formally, to fragile bodies comparable in strength to cometary meteoroids. The newly developed model of ablation of small iron meteoroids (Capek et al., 2019) is based on the spraying of liquid iron from the meteoroid surface. The model was able to derive unambiguous physical properties only for some of the studied cm-sized bodies. Another model, the semi–empirical model of meteoroid fragmentation, was used to fit the light curves. The erosion included in the model was able to fit the light curves by manually adjusting erosion parameters. To describe the sudden drop at the end of the light curve, it was necessary to progressively increase the erosion coefficient and decrease fragment masses along the trajectory.