The trail of sulphur: from molecular clouds to life

Introduction

Sulphur is the tenth most abundant element in the Universe and is known to play a significant role in biological systems. Moreover, some sulphur compounds have been proposed as necessary catalysts to form amino acids in the interstellar medium.

Current Knowledge Gaps

However, while the carbon and oxygen budgets have been extensively studied, sulphur is the only element whose gas-phase abundance is still uncertain by several orders of magnitude. This uncertainty hinders the usage of elemental sulphur abundance as a reliable tool to probe planet formation.

Reasons for Uncertainty

This lack of information is due to:

• The scarcity of observations, especially in protoplanetary disks.
• The still large uncertainties in the sulphur chemical network.

Project Objectives

This project takes a decisive step to fix our knowledge of the sulphur chemistry with an innovative methodology that rests on three pillars:

1. Database Creation: To create an unprecedented database of high-quality observations of sulphur-bearing molecules which allows us to trace the sulphur content from the natal molecular clouds to protoplanetary disks. Observations of the awarded IRAM Large Program GEMS have already provided part of this database.

2. Reaction Rate Estimation: To perform ab initio calculations and laboratory experiments to estimate the key reaction rates that are needed to fix the sulphur network and make chemical models reliable. Now, we know that the chemical composition of planet-forming disks is to a large extent inherited from the earliest phases of star formation.

3. Simulations: To perform bi-fluid (gas+dust) 3D magneto-hydrodynamics simulations with chemistry coupled (chemo-MHD) to follow the chemical evolution of the material from the natal cloud to the planet-forming sites, and hence, to obtain accurate chemical predictions. This can be extensively done by using artificial intelligence to reduce the computing time.

Conclusion

At the end, this project will disentangle how sulphur was delivered to protoplanetary disks, which is an essential step to understand planet formation and the emergence of life.