Gabriel Zachén

Thousands of tonnes of material from space, from space dust to meteors, fall to Earth every year. Of this material, a fraction survives the journey through the atmosphere and lands as meteorites. Some of these space rocks come from Mars, the Moon and comets, but the majority come from the asteroid belt between Mars and Jupiter. The asteroid belt is thought to be a collection of asteroids that were prevented from merging into a larger celestial body because of a tug-of-war between Jupiter and the inner solar system. As a result, the asteroid belt acts as a kind of archive of the solar system's past. Inscribed in ancient rocks are clues to how the Solar System - the Earth, the Moon and the other celestial bodies in our neighbourhood - formed and evolved.

My research focuses on a rare type of meteorite group: the mesosiderites. The name comes from the Greek: mesos, "inside"/"between"; and sideros, "iron". As the name suggests, these meteorites are composed of iron and stone, in roughly equal proportions. Mesosiderites have gone through several cycles of disintegration and reheating/melting as a result of collisions between celestial bodies at the beginning of the Solar System. Collisions between these were certainly nothing unique to the mesosiderites, but analysis of the metal and crushed rock material indicates that the metal came from a molten core of a celestial body, mixed into a cold crust! How this happened has long been disputed, and it is partly this that I want to answer.

The research project is divided into three parts:

1. Classification of the mineralogy, metamorphic grade, and shock grade of the pyroxene-rich mesosiderites. This will be done using optical microscopy and electron microscopy (SEM-EDS/EBSD). The aim is to be able to say what role collisions played in the formation and evolution of the mesosiderites. The analyses will mainly be carried out in Lund.
2. Analyses of noble gases and radionuclides will show how long the meteorites have been in space, which can tell us where they come from, and whether they are related to other meteorite groups. The analyses will be carried out at ETH Zürich (Switzerland) and at UC Berkeley (USA).
3. The final sub-project will look at when the metals in the mesosiderites were differentiated (separated from the silicates), and whether the metals come from the same celestial body as the crustal material. To determine this, we will analyze isotopes of hafnium and tungsten using mass spectrometry. The analyses will be carried out at Lawrence Livermore National Laboratory (USA).

Supervisors: Carl Alwmark (principal investigator, LU), Anders Scherstén (LU), Ludovic Ferrière (NHM Wien), Thomas Kruijer (LLNL), Matthias Meier (NHM Gallen), Henner Busemann (ETH)