The Potassium‐Argon Laser Experiment (<scp>KA</scp>r<scp>LE</scp>):<i>In Situ</i>Geochronology for Planetary Robotic Missions

摘要

Geochronology is a fundamental measurement for planetary samples, providing global and solar system context for the conditions prevailing on the planet at the time of major geological events. The potassium (K)‐Argon (Ar) laser experiment ( KA r LE ) will make in situ noble gas geochronology measurements aboard planetary robotic missions such as rovers and landers. Laser‐induced breakdown spectroscopy ( LIBS ) is used to measure the K abundance in a sample and to release its noble gases; the evolved Ar is measured by mass spectrometry, and relative K content is related to absolute Ar abundance by sample mass, determined by optical measurement of the ablated volume. This approach allows K and Ar to be measured on identical volumes multiple times to create an isochron, which improves the age determination and reveals irregularities in the rock if they exist. The KA r LE technique measures a whole‐rock K‐Ar age with 10% uncertainty or better for rocks 2 Ga or older, sufficient to resolve the absolute age of many planetary samples. The LIBS –mass spectrometry approach is attractive because the analytical components have been flight‐proven, do not require further technical development and provide essential measurements (complete elemental abundance, evolved volatile analysis, micro‐imaging) as well as in situ geochronology.