Achondrites in meteor data: Spectra, dynamics, and physical properties of candidate aubrite and eucrite impactors

TL;DR

This work demonstrates that achondritic meteoroids can be identified in meteor data through emission spectroscopy, improving the understanding of material diversity in the Solar System. By analyzing 180 high-resolution spectra with LTE radiative-transfer modeling, the authors identify two achondritic candidates—aaubrite-like and eucrite-like—and corroborate their compositions with relative abundances, light-curve behaviors, and dynamical histories. The aubrite-like object shows transient Ca, Mn, and Ti enhancements likely due to rapid volatilization of localized inclusions, while the eucrite-like object shows a compact, high-density ablation profile consistent with inner-main-belt delivery via the $\nu_6$ resonance. These results highlight the need for spectra in identifying achondrites in surveys and provide reference properties to improve future fireball network recovery and source-region linkage.

Abstract

Meteor spectroscopy presents new opportunities for investigating the diversity of small Solar System bodies and capturing the real distribution of present material types. We analyze 180 higher-resolution meteor spectra from the All-sky Meteor Orbit System (AMOS) network to identify meteoroids with atypical compositions. In addition to several iron bodies, we identify the first two achondritic meteoroids in our database, both likely meteorite-dropping impactors, and compare them with a reference ordinary chondrite meteoroid observed under similar conditions. Their spectra show strong compositional departures: one case has strong Mg and Si with low Fe, while the other has strong Ca, Al and Ti with low Mg. Derived relative elemental abundances imply an aubrite-like and a eucrite-like composition. The aubrite-like meteoroid exhibits unexpected enhancements in Ca, Mn and Ti in short-lived intensity spikes, which we interpret as rapid release of localized inclusions rather than bulk enrichment. This indicates that transient spectral features can reveal internal heterogeneity in achondritic meteoroids beyond their average composition. Dynamical and physical properties are consistent with these classifications: the eucrite-like meteoroid originated from an inner-main-belt orbit influenced by the $ν_6$ resonance and shows compact ablation with low erosion and an estimated bulk density of 3.16 $\pm$ 0.10 g cm -3; the aubrite-like meteoroid came from a short-period, low-eccentricity orbit similar to some E-type near-Earth asteroids. Both events show atypical light curves, but our results indicate that robust identification of achondritic meteoroids in surveys generally requires emission spectra. This work presents one of the first detailed studies of achondrites from meteor observations and provides reference properties of atypical meteors for future surveys.

Figures (9)

• Figure 1: Illustrative map of the AMOS network station locations, indicating the number of all-sky and spectral systems at each site.
• Figure 2: Stacked images from individual video frames of the spectra of achondrites ACH1 (upper panel), ACH2 (middle panel), and an ordinary chondritic meteoroid, M20240807_093858 (lower panel) as captured by the AMOS-Spec systems in Australia (ACH1) and Hawaii (ACH2 and the ordinary chondrite).
• Figure 3: Full calibrated spectral profiles of meteors ACH1 (the aubrite candidate) and ACH2 (the eucrite candidate). The most important identified emission lines are labeled.
• Figure 4: Comparison of the spectra of the two achondrites --- the aubrite candidate (ACH1; in blue) and the eucrite candidate (ACH2; in orange) --- with a typical ordinary-chondrite-like spectrum (black). The plots are split into separate wavelength ranges for better visibility, with intensities normalized to unity at the peak of the Fe I line at $\approx$ 527 nm. The aubrite candidate spectrum includes a more notable continuum and faint molecular bands of N2, which can be seen in the bottom two panels.
• Figure 5: Monochromatic light curves of the two candidate achondrites: ACH1 (upper panel) and ACH2 (lower panel), comparing the time-resolved emission of selected species, Mg I, Fe I, Mn I, and Ca I, based on selected well-resolved spectral lines. The time on the x-axis begins from the first recorded frame of the meteor spectrum.