Accretion and Early History of Planetesimals and Planets: The Noble Gas Record

Some of the distinct noble gas “components” in meteorites represent a record of processes during and even before solar system formation. This record is difficult to interpret. Often, one of the major problems is to recognize whether a certain noble gas elemental and isotopic pattern has been established in a presolar epoch, later in the solar accretion disk, during meteorite parent body formation or finally as a result of metamorphism on a parent body. It would also appear that noble gases are a preferred tool to deduce the types of matter from which the Earth and other planets accreted—if the respective parent materials are present in our extraterrestrial sample collections at all. However, also this issue is unsettled. Noble gas isotopes originating from the decay of radioactive precursors allow us to study the early and later degassing history of terrestrial planets, although the interpretation often remains model-dependent. This contribution briefly reviews some of the fundamental aspects of the noble gas record in meteorites and planets.