A Model of the Ordinary Chondrite Parent Body: An External Heating Model

By employing the best available constraints including the metamorphic temperature and the volume fraction of the type 6 chondrites in the parent body, we examined the external heating model for the ordinary chondrite parent body and compared the results with those obtained by the internal heating model. The Fourier number (k⊿ t/R^2) obtained is about 0.05 for the H-chon-drite parent body and about 0.15 for the L-chondrite parent body, respectively. The radius R for the H-chondrite parent body is 2-4km for ⊿ t∿(10)^5yr; 5-10km for ⊿ t∿(10)^6yr, where ⊿ t is the duration of the external heat source. For the Lchondrite parent body, the radius is about 0.6 times as large as that of the Lchondrite parent body. In the external heating model, the parent body of the ordinary chondrite must be small because of the short duration of the possible heat sources. The ordinary chondrite parent body (or bodies) may be the survivals (reheated and crushed afterwards, but not grown) of the planetesimals directly disintegrated from the dust layer in the primordial solar nebula.