# Where are the Water Worlds? Identifying the Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution

**Authors:** Aritra Chakrabarty, Gijs D. Mulders  
**arXiv:** [2310.03593](https://arxiv.org/abs/2310.03593)  
**Date:** 2023-10-05  
**Summary page:** https://www.summarizepaper.com/en/paper/2310.03593v1/

## Key points

- Chakrabarty and Mulders investigate water worlds among small exoplanets migrating from beyond the snowline of protoplanetary disks.
- Water worlds are believed to have water-ice-rich cores, comprising approximately 50% of their mass.
- Precise measurements of mass and radius suggest the existence of these water worlds.
- Different formation models combined with atmospheric escape models are used to address this issue.
- Migration models suggest at least 10% and 20% of bare planets without primordial H/He atmospheres around G- and M-type host stars respectively to be water-ice-rich.
- Most water worlds are predicted to exist outside an orbital period of 10 days.
- Radial velocity and transmission spectroscopy techniques may help identify these water worlds more effectively for planets with longer orbital periods.
- Further observations and investigations are needed to confirm the findings.

## Summary

In their study, Chakrabarty and Mulders investigate the presence of water worlds among small exoplanets that migrate from beyond the snowline of protoplanetary disks. These water worlds are believed to have water-ice-rich cores, comprising approximately 50% of their mass. While the observed radius valley of Kepler planets can be explained by the atmospheric dichotomy of rocky planets, there are indications from precise measurements of mass and radius that suggest the existence of these water worlds. To address this issue, the researchers combine different formation models from the Genesis library with atmospheric escape models such as photo-evaporation and impact stripping. By simulating planetary systems consistent with the observed radius valley, they aim to explore whether water worlds could be present in the currently observed sample. The results show that migration models suggest at least 10% and 20% of bare planets without primordial H/He atmospheres around G- and M-type host stars respectively to be water-ice-rich. These percentages align with the mass-radius distributions of observed planets. However, most water worlds are predicted to exist outside an orbital period of 10 days. To identify these water worlds more effectively, radial velocity and transmission spectroscopy techniques may prove successful when targeting planets with longer orbital periods. The authors emphasize that further observations and investigations are needed to confirm their findings. This study was supported by various research initiatives including Millennium Science Initiative (ICN12 009), ANID BASAL project FB210003, NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate, project "Alien Earths" funded under Agreement No. 80NSSC21K0593, and the Exoplanet Summer Program in the Other Worlds Laboratory (OWL) at the University of California Santa Cruz.