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13 February 2013
Bern computer simulation helps to better understand the origin of our solar
Simulations boost the significance of image and measurement data from space missions:
based on the example of an asteroid, Bernese astrophysicist Martin Jutzi shows how collisions
with other celestial bodies can be reconstructed and that even the internal structure of socalled
protoplanets can be described. These models help to understand the development of
our solar system. The study appears as today’s cover story in the journal Nature.
Four and a half billion years ago, dust particles in a giant, dusty gas cloud combined to form increasingly
large clumps. These collided, aggregated and thus grew into planets. Between the planetary orbits
of Mars and Jupiter, however, hundreds of thousands of smaller fragments remained. They
formed the so-called asteroid belt and hardly changed their composition since then. Asteroids thus
contain an inestimable amount of information on the origin of our solar system. In research, particular
attention is paid to an asteroid called Vesta: with a diameter of around 500 kilometres, it is one of the
three largest asteroids and considered to be a protoplanet. Moreover, it is the only known asteroid to
have an earth-like structure – with a core, mantle and crust.
Computer simulation reconstructs collisions between asteroids
Using a three-dimensional computer simulation, Martin Jutzi from the Center for Space and Habitability
(CSH) at the University of Bern has now accurately reconstructed how Vesta collided with other
asteroids twice over a billion years ago. The models show that the protoplanet owes its elliptical shape
to these collisions and that they also scarred its surface structure. The simulations also enable detailed
conclusions on the composition and properties of Vesta’s interior to be drawn for the first time,
which helps us to better understand the evolution of the solar system. After all, the formation of
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planets largely depends upon collisions between celestial bodies. «Our method facilitates especially
informative analyses of image and measurement data from space missions,» says Martin Jutzi. The
study, which was conducted in collaboration with researchers from the EPFL, France and the USA,
features as the cover story in today’s issue of Nature.
Models uncover hidden secrets
Previously, observations with the Hubble Space Telescope provided initial evidence of a giant crater at
Vesta’s south pole. Then, in 2007, NASA’s «Dawn» probe began its space voyage into the solar system’s
past. Starting in the summer of 2011, it closely orbited Vesta for one year. Images from within
the visible range as well as other measurement data provided information on the asteroid’s topography
and the composition of the minerals that are visible on its surface. It became apparent that the
crater observed by Hubble at Vesta’s south pole is actually composed of two partially overlapping basins.
Based on this information, the computer simulations by Jutzi’s team now demonstrate exactly how two
consecutive impacts of celestial bodies led to the formation of the observed overlapping basins, which
almost span the entire southern hemisphere of Vesta. The models show the size (66 and 64 kilometres
in diameter), velocity (5.4 kilometres per second) and the impact angle of the bodies that collided
with Vesta. This reveals a lot about the properties of the objects that were near the protoplanet a billion
The final images of the simulations closely resemble the shape and topography of Vesta’s southern
hemisphere as observed by the Dawn mission. The models even accurately reproduce the spiralshaped
structures inside the youngest crater which are visible on images from the Dawn mission.
«This shows how reliable our method is,» rejoices Jutzi. The researchers assume that the models also
provide information about previously hidden features of Vesta. For instance, the simulations reveal
that the material exposed by the impacts comes from depths of up to 100 kilometres. «Based on the
sort and distribution of this material we are able to precisely reconstruct the various inner layers of
Vesta,» explains Philippe Gillet, Direktor des Earth and Planetary Science Laboratory der EPFL.
«The fact that we can now look inside such protoplanets makes entirely new perspectives in the research
on the history of our solar system possible,» says Jutzi.
M. Jutzi, E. Asphaug, P. Gillet, J.-A. Barrat, W. Benz: The structure of the asteroid 4 Vesta as revealed
by models of planet-scale collisions, Nature, 14 February 2013, in print.
Dr Martin Jutzi, Center for Space and Habitability (CSH), Universität Bern
+41 31 631 85 49 / firstname.lastname@example.org
Prof. Dr Philippe Gillet, Earth and Planetary Science Laboratory, EPFL
+41 21 69 370 58 / email@example.com
Prof. Dr Willy Benz, Center for Space and Habitability (CSH), Universität Bern
+41 31 631 44 03 / firstname.lastname@example.org