The Oort cloud as inner solar system exhaust: combustion products from magma ocean methane oxidation as a source of outer solar system volatiles

A companion paper (Jenkins 2026, ESSOAr) demonstrates that magma ocean methane combustion is a thermodynamically inevitable source of terrestrial water. Here we note a corollary: during the magma ocean phase, inner solar system bodies at surface temperatures of 1,000-1,500°C produced water vapour, CO 2 , and residual hydrocarbons as reaction products. A significant fraction of these volatiles exceeded escape velocity, particularly from the equatorial regions of rapidly rotating early planets. Ejected material migrated outward under solar radiation pressure and froze in the outer solar system. We propose that the Oort cloud and portions of the Kuiper belt include inner solar system combustion exhaust-not exclusively pristine presolar ices. This reframes cometary water delivery to Earth as partial return of material that originated from inner solar system oxidation reactions rather than primordial outer solar system condensation. The recent discovery of rocky inner solar system material in the Oort cloud (C/2014 S3) with anomalously low volatile content supports this framework. Testable predictions include isotopic signatures of thermal processing in Oort cloud comets and a correlation between cometary D/H ratios and indicators of inner solar system origin.