Project 5
The study of the origin of the Solar System is one of the cornerstones towards a full understanding of the origin and evolution of planetary systems in general. Indeed, our knowledge of the chemical, isotopic, and dynamic state of the Solar System lies way beyond what can be obtained for extrasolar planetary systems, and any general models for planet formation have to reproduce our own Solar System as one possible result.
During the last two decades we have developed the “Bern model”, a multi-planetary system formation and evolution model that incorporates many physical aspects relevant during planet formation. In a population synthesis approach, our recent results show that the predictions of the models match the observation of planetary systems well on the single planet level (e.g., mass function, etc.) and also in terms of planetary architecture (e.g., the so-called “peas-in-a-pod” effect, the correlation between planetary types in a given system). The next natural step is addressing the question whether the same model can also reproduce the Solar System. This key scientific question will be the subject of this project.
The very question of “Does the Bern model reproduce the Solar System?” is by itself difficult, since answering it requires first to define which properties of the Solar System have to be considered. Our approach is to proceed step-by-step by implementing finer and finer constraints, checking at each step if the formation model does match these constraints, and if not, which physical processes need to be added to the model to fulfil these constraints. Evidently, one key constraint here is that improving the match with the Solar System must be done while preserving the fair agreement with the population of extrasolar planets.
The project will be divided in 5 work packages (WP) that will address different parameters relevant for the models. In each of the four first work packages we will consider different types of observational constraints, from the ones already included in former models (WP1 and WP2) to the ones that will require developing models (isotopic ratios and orbital dynamics of small bodies). In the last work package, we will consider what could be learned from the Solar System by remote observation, in analogy with what can be done for extrasolar planets. All the WPs will build on initial pilot studies from the first two phases of the NCCR PlanetS. In addition, all WPs will take advantage and strengthen interactions with colleagues in the different NCCR PlanetS nodes.
Work Package 1: Mass and orbital elements.
The first work package is dedicated to finding possible initial conditions (disc properties in particular) that can lead to planetary systems that are similar to the Solar System. Initial calculations have shown that this is indeed possible, but only for in situ formation models, whereas the population of exoplanets is better matched with models including migration. Some process seems to have been at work during the formation of the Solar System that stopped giant planets to migrate. One explanation for this observation could be provided by the so-called Masset-Snellgrove mechanism, which requires some special conditions to operate. The goal of the work package will be to evaluate to what extent such processes can reproduce the formation of the Solar System while at the same time lead to a full population of planets similar to that observed. Additionally, we will determine the initial conditions (e.g., disc properties) required in order for a system like the Solar System to emerge.
Work Package 2: Planetary building blocks and the bulk composition of planets.
In the second work package, we will model the bulk composition of planets, combining the formation models from WP1 with the composition of planetary building blocks following our past work on the subject (Thiabaud et al. 2015) and with Project C2. The chemical and isotopic composition of the planetary building blocks will be constrained from both solar system and ALMA data in collaboration with Project A8. In addition, we will take advantage of the possibility of visiting and observing a dynamically new comet with Comet Interceptor. These objects may indeed preserve more basic properties than evolved comet nuclei, and observations from Comet Interceptor can potentially strongly constrain the composition of planetary building blocks. Moreover, thermal and physical properties of solids (pebbles) will be updated considering results of experiments whose development started during Phase II. Finally, the link between the composition of the upper atmosphere (the observed one) and the bulk one (result of models) will be done in Project B1.
Work Package 3: Chemical and isotopic trends.
In the third work package, we will use the models from WP1 and the work done in Project A1 to predict the chemical and isotopic trends (e.g., Cr, Ti, Mo isotope variability) and compare them, using meteoritic analysis, to the ones that can be found in different bodies of the Solar System. We will for example compute the expected 18O/17O/16O isotopic ratios in the different formation models and compare them to observed data. Indeed, in addition to potential primordial heterogeneity in the O isotopic ratio, mass independent fractionation of O isotopes occurred as a result of the interaction between UV light emanating from the early Sun and CO2 present in the protoplanetary disc (Young 2007). Such variations can inform us on the origin of the material that took part to the formation of different bodies in the Solar System. Finally, we will compute the abundance of elements as a function of their volatility and compare this to measurements, following our recent study (Vollstaedt et al. 2020). This will constrain the pressure-temperature evolution in different regions of the solar nebula.
Work Package 4: Minor body timescales.
In this work package, we will compute the evolution of the orbital elements of minor bodies for different models, using state-of-the art N-body codes in collaboration with Projects A2 and A3. Indeed, preliminary studies show that the orbital elements of small bodies in the vicinity of Jupiter could depend on the gas accretion rate of forming planets. Our calculations, coupled with the composition study in WP2, will also determine the expected flux of material from the outer Solar System which contributes to the water budget of terrestrial planets. In this WP, we will also compare the chronology of important events in the Solar System (Jupiter formation, formation of planetesimals and the terrestrial planets, lifetime of the solar nebula) with the results obtained by the models.
Work Package 5: Solar system planets as exoplanets.
This last work package will be developed in interaction with Projects C2 and C3. Using results of formation models as test cases, we will infer what parameters of planets and planetary systems could be retrieved for the Solar System if it were to be observed spectroscopically from a few parsecs away. This comparison will be done for different ages of the Solar System, in order to inform the detectability of systems analogues to ours at different steps of their evolution.
