Fachbereich 14 - Geowissenschaften
Institut für Planetologie
Analytische Planetologie

The early thermal history of the H-chondrite parent asteroid from
integrate 244Pu and 40Ar-39Ar thermochronometries

Most meteorites are fragments from asteroids. For some of these (e.g., the parent bodies of basaltic achondrites) accretion, heating and differentiation into silicate crusts and metallic cores occurred within a few million years after condensation of the first refractory minerals in the early solar nebula. Radiometric dating evidenced that the basaltic crust cooled rapidly, while the metallic cores needed some tens of million years for cooling as inferred from Fe-Ni profiles in iron meteorites. Other asteroids, the parent bodies of undifferentiated chondritic meteorites, experienced comparatively mild thermal metamorphism with maximum temperatures that were insufficient to separate metal from silicate. We obtained new results on H chondrites in a comprehensive study of ²⁴⁴Pu fission track and ⁴⁰Ar-³⁹Ar thermochronologies. These results unequivocally demonstrate that - after fast accretion - primordial heating (most probably due to ²⁶Al decay) led to a layered parent body structure. Rocks in the outer shells reached lower maximum metamorphic temperatures and cooled faster than the more re-crystallized and chemically equilibrated rocks from the center that needed ~160 Ma to reach 390 K. Obviously, the layered parent body was not destroyed by early impacts. Fragmentation and re-assembly processes causing the presently observed rubble pile structures of asteroids most probably occurred later.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligter Wissenschaftler:

Elmar K. Jessberger et al.

Veröffentlichungen:

M. Trieloff, E.K. Jessberger, I. Herrwerth, J. Hopp, C. Fiéni, M. Ghélis, M. Bourot-Denise, P. Pellas (2003): The early thermal history of the H-chondrite parent asteroid from integrated ²⁴⁴Pu and ⁴⁰Ar-³⁹Ar thermochronometries. Nature 422, 502-506.