Planetary Science Researcher (M/F) - Junior

Job Description

Missions

One of the longstanding challenges in planetary science is to understand the mechanisms that drive the accretion of planetesimals, the first planetary bodies to form in protoplanetary disks. Intuitively, one could expect that km-size planetesimals grow by gradual accretion of smaller aggregates, but this scenario is made implausible by the high probability of break up upon collision of the aggregates and their rapid accretion onto the central star.
Lifting the barrier to accretion requires drastically reducing the time needed for dust particles to aggregate. This is the case for the mechanism of gravitational collapse, whereby swarms of particles may reach a density threshold triggering their collapse into km-sized planetesimals. Observational cues in favor of this mechanism exist (e.g., the abundance of large binary asteroids in the outer solar system) but are particularly rare, given the fact that most asteroid populations are no longer representative of the first planetesimals.
Models of gravitational collapse predict the size-frequency distribution (SFD) of the planetesimal population post accretion. One approach to test the validity of these models is to use collisional evolution models, which simulate the dynamical evolution of initial planetesimal SFD and compare the outcome to the current asteroid population. However, the problem is ill-posed, because several initial SFDs can match today's observations within uncertainties. There is a need for complementary ways to characterize the solar system's initial SFD.
The metallographic microstructures found in meteorites are directly related to the thermal history, and therefore the size, of their parent planetesimals. A systematic survey of meteorite parent body sizes therefore appears like an alternative way to place constraints on the SFD of a subsample of the planetesimal population. Of particular interest for this task are the iron meteorites, thought to have formed in planetesimal cores, both in the inner and outer solar system. The cooling rates of iron meteorites reflect the thickness of the silicate mantle overlying the core and as such directly relate to the size of the body.

Activity

The overarching objective of the project is to estimate the parent body size for the majority of iron meteorite groups, and compare them to the predicted planetesimal SFD found in the literature. As a mean to estimate the parent body size, it is proposed to determine, for multiple meteorites of each group, their cooling rates in two temperature ranges. This can be done by combining SEM analyses with numerical models of formation of the meteoritic metallographic microstructures, which are based on diffusion equations and parameters in Fe-Ni alloys. Previous studies of iron meteorite cooling rates are only valid in the 700-500°C temperature range. Here, the novelty of the approach resides in the determination of two cooling rates that can be combined to provide more reliable constraints for planetesimal thermal models

The project is foreseen in four axes, though it is up to the candidate to find an alternative approach or build upon the proposed one:
1. Update and improve the models of formation of the metallographic microstructures,
2. Collect data and determine metallographic cooling rates for all iron meteorite groups,
3. Develop or adapt a planetesimal cooling model to determine the parent body size,
4. Compare the empirical size distribution to the SFD predicted by different accretion models.

Your Profil

Skills

The candidate should hold a PhD in the broad fields of metallurgy, planetary science, mineralogy, or material science. Expertise in some of the following domains (or strong motivation to acquire one) is expected: iron meteorites, petrography, SEM, EDS, EBSD, phase diagrams, solid-state diffusion, thermal modelling, coding (python).

Your Work Environment

CEREGE is located on the Petit Arbois plateau, Technopole Environnement Arbois - Méditerranée, Avenue Louis Philibert, Les Milles-Aix-en-Provence. The successful candidate will join CEREGE's Earth and Planets team and work in collaboration with several team members: Dr. Jérôme Gattacceca, Dr. Clara Maurel, Professor Bertrand Devouard, and Dr. Minoru Uehara.

Compensation and benefits

Compensation

betwen 3131.32 et 3569.85 gross salary per month

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

The research professions