S. Marchi, M. Massironi, J. -B. Vincent, A. Morbidelli, S. Mottola, F. Marzari, M. Kueppers, S. Besse, N. Thomas, C. Barbieri, G. Naletto, H. Sierks
The European Space Agency's Rosetta spacecraft passed by the main belt
asteroid (21) Lutetia the 10th July 2010. With its ~100km size, Lutetia is one
of the largest asteroids ever imaged by a spacecraft. During the flyby, the
on-board OSIRIS imaging system acquired spectacular images of Lutetia's
northern hemisphere revealing a complex surface scarred by numerous impact
craters, reaching the maximum dimension of about 55km. In this paper, we assess
the cratering history of the asteroid. For this purpose, we apply current
models describing the formation and evolution of main belt asteroids, that
provide the rate and velocity distributions of impactors. These models, coupled
with appropriate crater scaling laws, allow us to interpret the observed crater
size-frequency distribution (SFD) and constrain the cratering history. Thanks
to this approach, we derive the crater retention age of several regions on
Lutetia, namely the time lapsed since their formation or global surface reset.
We also investigate the influence of various factors -like Lutetia's bulk
structure and crater obliteration- on the observed crater SFDs and the
estimated surface ages. From our analysis, it emerges that Lutetia underwent a
complex collisional evolution, involving major local resurfacing events till
recent times. The difference in crater density between the youngest and oldest
recognized units implies a difference in age of more than a factor of 10. The
youngest unit (Beatica) has an estimated age of tens to hundreds of Myr, while
the oldest one (Achaia) formed during a period when the bombardment of
asteroids was more intense than the current one, presumably around 3.6Gyr ago
or older.
View original:
http://arxiv.org/abs/1111.3628
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