# Born Dry or Born Wet? A Palette of Water Growth Histories in TRAPPIST-1 Analogs and Compact Planetary Systems

**Authors:** Howard Chen, Matthew S. Clement, Le-Chris Wang, Jesse T. Gu  
**arXiv:** [2510.12794](https://arxiv.org/abs/2510.12794)  
**Date:** 2025-10-14  
**Summary page:** https://www.summarizepaper.com/en/paper/2510.12794v1/

## Key points

- Chen et al. study the ability of exoplanets in compact multiplanet systems to accrete volatiles and maintain atmospheres and hydrospheres.
- Factors considered include impact delivery, erosion, mantle-atmosphere exchange, and volatile evolution during the pre-main-sequence phase of M dwarfs.
- Inner TRAPPIST-1 analogs (b-e) have lower water inventories ($10^{-4}$ to $10^{-2} M_{\oplus,\rm ocn}$) compared to outer planets (f-h analogs), which often retain water inventories surpassing an Earth ocean mass.
- No atmospheres detected on TRAPPIST-1 b and c by JWST may be due to volatile depletion during formation rather than post-formation loss.
- Rocky planets in compact M-dwarf systems may originate with limited volatile compounds, potentially limiting their ability to sustain atmospheres or surface oceans.
- The multistage framework developed by Chen et al. can help interpret future observations of compact planetary systems and establish more realistic initial conditions for modeling exoplanet interiors and atmospheres.

## Summary

In their study titled "Born Dry or Born Wet? A Palette of Water Growth Histories in TRAPPIST-1 Analogs and Compact Planetary Systems," Chen et al. investigate the ability of exoplanets in compact multiplanet systems to accrete volatiles and maintain atmospheres and hydrospheres. They consider various factors such as impact delivery, erosion, mantle-atmosphere exchange, and volatile evolution to develop a comprehensive model for planetesimal accretion during the pre-main-sequence phase of M dwarfs. The results show that inner TRAPPIST-1 analogs (b-e) have lower water inventories ranging from $10^{-4}$ to $10^{-2} M_{\oplus,\rm ocn}$ compared to outer planets (f-h analogs), which frequently retain water inventories surpassing an Earth ocean mass. This gradient in volatile content may explain why no atmospheres have been detected on TRAPPIST-1 b and c by JWST, suggesting that their formation conditions may have led to volatile depletion rather than post-formation loss. These findings suggest that many rocky planets in compact M-dwarf systems may originate with limited volatile compounds, limiting their potential for sustaining atmospheres or surface oceans. The multistage framework developed by Chen et al. can aid in interpreting future observations of compact planetary systems and establishing more realistic initial conditions for modeling exoplanet interiors and atmospheres. Overall, this study sheds light on the complex processes involved in planetary formation and evolution within densely packed planetary systems like TRAPPIST-1, providing valuable insights into the potential habitability of exoplanets across different regions within these systems.