# Carbon Depletion in the Early Solar System

**Authors:** Fabian Binkert, Til Birnstiel  
**arXiv:** [2301.05706](https://arxiv.org/abs/2301.05706)  
**Date:** 2023-01-13  
**Summary page:** https://www.summarizepaper.com/en/paper/2301.05706v1/

## Key points

- Earth and other rocky objects in the inner Solar System have less carbon compared to objects in the outer Solar System, the Sun, or the interstellar medium (ISM).
- The selective removal of refractory carbon from primordial circumstellar material is responsible for this difference.
- Photolysis and pyrolysis of refractory carbonaceous material were considered to understand how carbon was released into the gaseous environment during the disk phase of the early Solar System.
- Neither depletion mechanism alone can reproduce Solar System abundances under typical conditions.
- An increase in vertical mixing efficiency or directly irradiated disk volume favors carbon depletion.
- For thermal decomposition to occur, a hot inner disk (> 500 K) beyond 3 AU is required to deplete Earth's formation region as well as chondrites.
- FU Ori-type outbursts are capable of producing these conditions such that moderately refractory compounds are depleted. However, such outbursts likely do not deplete the most refractory carbonaceous compounds beyond the innermost disk region.
- Under specific conditions, photolysis and pyrolysis combined can reproduce Solar System abundances.

## Summary

In this study, Fabian Binkert and Til Birnstiel investigate the depletion of carbon in the early Solar System. They note that Earth and other rocky objects in the inner Solar System have less carbon compared to objects in the outer Solar System, the Sun, or the interstellar medium (ISM). The authors attribute this difference to the selective removal of refractory carbon from primordial circumstellar material. To understand how carbon was released into the gaseous environment during the disk phase of the early Solar System, they consider photolysis and pyrolysis of refractory carbonaceous material. Using an analytical approach, Binkert and Birnstiel solve a one-dimensional advection equation and derive an explicit expression that describes how carbonaceous material is depleted in solids under radial and vertical transport. They find that neither depletion mechanism alone can reproduce Solar System abundances under typical conditions. While radial transport only marginally restricts photodecomposition, it is inefficient vertical transport that limits carbon depletion under these conditions. The authors show explicitly that an increase in vertical mixing efficiency or directly irradiated disk volume favors carbon depletion. For thermal decomposition to occur, a hot inner disk (> 500 K) beyond 3 AU is required to deplete Earth's formation region as well as chondrites. They find FU Ori-type outbursts capable of producing these conditions such that moderately refractory compounds are depleted. However, such outbursts likely do not deplete the most refractory carbonaceous compounds beyond the innermost disk region. As a result, refractory carbon abundance at 1 AU typically does not reach terrestrial levels. Nevertheless, under specific conditions, photolysis and pyrolysis combined can reproduce Solar System abundances. Overall, this study sheds light on how different mechanisms affect carbon depletion during early Solar System evolution and provides insights into why Earth has less carbon than other objects in our solar system.