Determine the composition and structure of 3I/ATLAS’s pristine interior

Determine the composition and physical structure of the pristine, unprocessed interior of interstellar comet 3I/ATLAS that is shielded from galactic cosmic rays beneath the approximately 15–20 m GCR-processed crust, in order to characterize how it differs from the irradiated outer layers.

Background

The paper argues that long-term galactic cosmic ray irradiation transforms the outer ~15–20 m of interstellar comet nuclei, converting CO to CO2, generating organic-rich crusts, and compacting ice. Observations of 3I/ATLAS show extreme CO2/H2O and elevated CO/H2O ratios, consistent with GCR processing rather than pristine composition.

Given that pre-perihelion erosion depths are much smaller than the GCR-processed layer thickness, current outgassing likely samples only altered material. The authors explicitly note that the composition and structure of the deeper, pristine interior remain unknown but are expected to differ from the irradiated crust, motivating targeted observations to probe or infer the interior properties.