Phd Defense : Marin Ferrais

“Constraining the formation and evolution of the largest main belt
asteroids”

Abstract

Asteroids in our Solar System exhibit a wide variety of sizes, shapes,
compositions, and orbital properties and provide powerful constraints
for planetary system formation models. However, little is known
regarding their densities and internal structure although these are
fundamental properties that derive from the formation conditions and
collisional evolution.
An ESO large program was conducted with the VLT/SPHERE/ZIMPOL adaptive
optics instrument to image a significant sample of the largest (D >
100 km) main belt asteroids, covering the main compositional classes.
The detailed disk-resolved images allowed to derive their volumes via
3D shape modelling, thus their densities when combined with mass
estimates.
Detailed 3D shape models were produced using the method MPCD and
lightcurves were acquired with the TRAPPIST telescopes. The results
encompass the dedicated studies of two particular asteroids, (16)
Psyche and (22) Kalliope and the quantitative analysis of the complete
sample of shape models.
Psyche and Kalliope are both metallic rich asteroids whose densities
were found to be among the highest known for small bodies. The
obtained 3D shape of Psyche, which is the target of a forthcoming NASA
discovery mission, implies a primordial shape close to that of a
Jacobi ellipsoid. The high bulk density of Kalliope strongly suggests
a differentiated interior. The analysis of the 42 reconstructed shape
showed a division in two families of objects, the spherical and the
elongated. Finally, the large difference in the derived densities
provided clues about the origins of the main compositional classes.

Jury members:

Sylvain Douté, IPAG – Referee

Simone Marchi, SwRI – Referee

Antonella Barucci, LESIA – Examiner

Richard P. Binzel, MIT – Examiner

Olivier Mousis, LAM – President

Pierre Vernazza, LAM – Advisor

Laurent Jorda, LAM – Co-Advisor