The Winchcombe Fireball -- that Lucky Survivor

TL;DR

The Winchcombe fireball was a rare, low-mass carbonaceous meteoroid that survived atmospheric entry due to low velocity and dynamic pressure, providing insights into the fragility and orbital history of such meteorites.

Contribution

This study reconstructs the trajectory, fragmentation, and orbit of a small, fragile carbonaceous meteoroid, revealing conditions that enable survival during atmospheric entry.

Findings

Meteoroid was about 13 kg, much smaller than typical carbonaceous falls.

Survived due to low entry velocity (13.9 km/s) and dynamic pressure (~0.6 MPa).

Orbital analysis shows it originated ~0.08 Myr ago with a perihelion >0.7 AU.

Abstract

On February 28, 2021, a fireball dropped $\sim0.6$ kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behaviour, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive ($\sim13$ kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure ($\sim0.6$ MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km/s). A near-catastrophic fragmentation at $\sim0.07$ MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region $\sim0.08$ Myr ago and it never had a perihelion distance smaller than $\sim0.7$ AU, while other CM2 meteorites with known orbits approached the Sun closer ($\sim0.5$ AU) and were heated to at least 100 K higher temperatures.