A THEORY OF LOCAL FORMATION OF ISOTOPIC ANOMALIES IN METEORITES

The consequences of a postulated collision between planets in the earl y solar system have been investigated. At least one of the planets has been taken with a D/H ratio similar to that of Venus (0.016) and the temperature of the collision interface (similar to 3 X 10(6) K) trigge rs chain reactions in near-surface material beginning with D-D reactio ns. The initial composition of the reacting material is consistent wit h a silicate + ices surface and a hydrogen-helium inert gas atmosphere . The reaction chain contains 284 reactions, plus reverse reactions, a nd 40 radioactive decay processes. When the pressure in the reacting r egion is sufficiently high the colliding planets are blown apart and t he highly-processed material at the heart of the explosion mixes with less processed and unprocessed material from cooler parts of the syste m. Mixtures of materials are found to explain isotopic anomalies assoc iated with oxygen, magnesium, neon, silicon, carbon and nitrogen. The local production of isotopic anomalies avoids the problems associated with other suggested explanations - in particular the observation of n eon E, almost pure Ne-22, assumed as the product of the decay of Na-22 with a half-life of 2.6 years.