Dix Planetary Science Seminar

Abstract:

Depending on the accretion time of an asteroid, it is thought to have

either partially melted and differentiated entirely shortly after

accretion or remained completely unmelted and undifferentiated

throughout its history. However, paleomagnetic measurements of

chondrites (meteorites that remained unmelted and undifferentiated on

their parent asteroids) suggest that some of these meteorites

experienced magnetic fields with properties consistent with those

generated by core dynamo activity. This observation suggests that the

parent asteroids of these meteorites contained convecting metallic

cores, implying that they were composed of an unmelted exterior atop a

partially molten interior and were therefore partially differentiated.

Magnetic measurements supporting the existence of this type of bodies

have largely been conducted on samples that experienced complex and

relatively short-lived thermal and aqueous histories on their parent

asteroids, which complicates the interpretation of some of these

measurements. Here, I will present paleomagnetic measurements of

slowly-cooled, water-poor meteorites with well-constrained thermal and

impact histories as well as a new paleomagnetic technique capable of

measuring the magnetic remanence carried by such meteorites. These

measurements indicate that some chondrites experienced late-stage

magnetic activity on their parent asteroids, providing a new set of

observations favouring partially differentiated asteroids. I will also

present results of asteroid thermal evolution models that suggest

partially differentiated bodies could have formed through incremental

accretion over <4 Myr. Together, these observations challenge

conventional views on the duration of asteroid accretion, the internal

structure of asteroids with primitive surfaces and the potential origins

of different meteorite groups.