The First Instrumentally Documented Fall of an Iron Meteorite: atmospheric trajectory and ground impact

TL;DR

This paper documents the first instrumentally recorded fall of an iron meteorite, combining multiple data sources to analyze its atmospheric trajectory, ground impact, and unique properties, advancing understanding of iron meteoroid behavior.

Contribution

It presents the first reliable pre-atmospheric orbit and detailed trajectory analysis of an iron meteorite fall, incorporating iron-specific aerodynamic parameters into entry models.

Findings

First iron meteorite with a derivable heliocentric orbit.

Identified unique aerodynamic properties of iron meteoroids.

Improved models for predicting iron meteorite strewn fields.

Abstract

Iron meteorite falls are rare compared to stony meteorites, and until recently no iron meteorite had a reliably determined pre-atmospheric orbit. This changed on 2020 November 7, when a bright fireball was observed across Sweden and neighboring regions, with optical, acoustic, and seismic detections extending up to 665 km from the trajectory. After a month-long recovery effort, a 13.8 kg iron meteorite was discovered near {\AA}dalen, representing the first instrumentally recorded and recovered fall of its type and the first iron meteorite with a derivable heliocentric orbit; the event also exhibited the lowest terminal height measured for a well-documented fireball. We combine optical, infrasound, and seismic data to reconstruct the luminous trajectory and employ a Monte Carlo model to simulate the dark flight phase and predicted strewn field, while also investigating the plausibility of a ricochet prior to final deposition. Our analysis identifies distinct aerodynamic properties of iron meteoroids compared to stony bodies, including the influence of streamlined shapes and deep regmaglypts on drag and flight stability, underscoring the need to incorporate iron-specific parameters into entry models to constrain atmospheric dynamics and improve recovery predictions for future events.