Constraints on planetesimals formation from their thermal evolution
Meteorites record the information during their formation process in the
early solar system. They originate from asteroids, which are remnants of
planetesimals. Their formation process, including size and formation time,
has not been established. In this talk, I would like to present some
constraints on the planetesimals from their thermal modeling, in
particular, the parent body of the asteroid Itokawa
(Wakita et al. 2014).
Study of dust particles returned from asteroid Itokawa indicates that their
parent body was heated at a peak temperature of 800 degree Celsius (but
less than 1000 degree Celsius) and also kept higher than 700 degree Celsius
at 7.6 Myr after Ca-Al rich inclusion (CAI) formation, which is about 4567
Myr ago (Nakamura et al. 2011; Yurimoto et al. 2011). We numerically
perform thermal evolutions of planetesimals, assuming they are
instantaneously-accreted, spherically symmetric bodies, and heated from
inside by the decay of the short-lived radionuclide aluminum-26.
Our results demonstrate that Itokawa's parent bodies were at least 20 km in
radius, and accreted between 1.9 and 2.2 Myr after CAIs. If Itokawa's
parent bodies were typical, this yields sizes and formation time for
planetesimals in the vicinity of the asteroid belt.