Carbon reactions during impacts reveal why meteorites seem less shocked

Meteorite collisions serve as time capsules, preserving clues about the early solar system. However, meteorites rich in carbon have long appeared to bear fewer signs of violent impacts, an anomaly that suggested lower collision speeds without a clear explanation. "I specialize in impact physics and am interested in how the meteorite material changes in response to impacts, something called 'shock metamorphism.' And so I was very interested in this question," explained Kobe University astrophysicist KUROSAWA Kosuke.

Years ago, another Kobe University researcher hypothesized that vapor released during impacts could drive away shocked material. Inspired by this idea, Kurosawa sought to explore it more rigorously. He pointed out that prior models lacked calculations of vapor production volumes and could not explain the behavior of carbon-rich meteorites that lacked water-bearing minerals.

To address this, Kurosawa used a custom-built experimental system: a two-stage light gas gun linked to a vacuum sample chamber. This setup enabled his team to study the chemical reactions triggered by impacts on meteorite analogs containing or lacking carbon, without interference from extraneous gases.

Published recently in Nature Communications, the Kobe University team's findings demonstrate that impacts on carbon-containing meteorites trigger chemical reactions that generate extremely hot carbon monoxide and carbon dioxide gases. "We found that the momentum of the ensuing explosion is enough to eject the surrounding highly-shocked rock material into space. Such explosions occur on carbon-rich meteorites, but not on carbon-poor ones," Kurosawa noted.

Thus, carbon-rich meteorites are not less shocked-they simply lose the evidence as it is violently expelled into space during impact events.

This discovery carries implications for planetary science missions. The team's calculations suggest that on larger bodies like Ceres, gravity could retain the ejected shocked material on the surface. "Our results predict that Ceres should have accumulated highly-shocked material produced by these impacts, and so we believe that this provides a guideline for planning the next generation of planetary exploration missions," Kurosawa added.

Research Report:Impact-driven oxidation of organics explains chondrite shock metamorphism dichotomy