20-EPN2-098: Constraining the Thermal History of Water-Rich Asteroids Using Noble Gas Analysis of Heated CM Chondrites
Visit by Ashley King and Helena Bates (Natural History Museum, UK) to TA2.15 ETH Zurich Geo- and Cosmochemistry Isotope Facility (Switzerland).
Dates of visit: 28 November – 08 December 2022
In this TA visit, the team investigated the abundance and isotopic composition of noble gases (He – Xe) in CM chondrites that record both aqueous and thermal metamorphism. These unusual meteorites are likely good analogues for the types of material found on the surfaces of primitive C-type asteroids; however, the timing and mechanism of the metamorphism remains unknown.
The team measured He – Xe in five CM chondrites that experienced peak metamorphic temperatures of <300°C to >750°C using stepped-heating and the “ALBATROS” mass spectrometer at the ETH Zürich Geo- and Cosmochemistry Noble Gas Laboratory. Preliminary results show that the concentrations of 4He and 22Ne are depleted in the lowest temperature steps (300 and 450°C) for all samples, consistent with degassing during (a) metamorphic event(s). Peaks in the concentration of both light and heavy noble gases in the 660°C and 800°C steps agree with previous estimates of metamorphic temperatures based on mineralogy and H2O loss. Isotopic compositions are mainly a mixture of primordial (so-called Q/HL) and cosmogenic components. In addition, EET 96029 and WIS 91600 contain a trapped solar wind component, suggesting that these meteorites may have been heated by impacts during residence in the asteroid regolith. Comparison of the data to unheated CM chondrites will be used to further constrain the thermal history of C-type asteroids in the early Solar System.
Read the full scientific report with kind permission by Ashley King and Helena Bates.