# The clumpy structure of $ε$ Eridani's debris disc revisited by ALMA

**Authors:** Mark Booth, Tim D. Pearce, Alexander V. Krivov, Mark C. Wyatt, William R. F. Dent, Antonio S. Hales, Jean-François Lestrade, Fernando Cruz-Sáenz de Miera, Virginie C. Faramaz, Torsten Löhne, Miguel Chavez-Dagostino  
**arXiv:** [2303.13584](https://arxiv.org/abs/2303.13584)  
**Date:** 2023-03-23  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.13584v1/

## Key points

- A recent study revisited the debris disc surrounding $\epsilon$ Eridani, the closest star to our Sun known to host such a disc.
- Previous observations suggested that clumpy structures in the disc were due to interactions with an undetected planet, but could not distinguish between background confusion and structure in the disc.
- The new study presents the first ALMA image of the entire disc, which clearly detects the star, main belt and two point sources.
- Two clumps with $>3\sigma$ significance remain in the main belt - one to the east of the star and another to its northwest after accounting for background galaxies (point sources) and disc emission.
- $n$-body simulations showed how migrating planets can create similar structures by trapping planetesimals in resonances.
- A migrating planet could reproduce observed features by trapping planetesimals in a 2:1 mean motion resonance, and that symmetry of prominent clumps indicated that such a planet should have either ${\sim10^\circ}$ or ${\sim190^\circ}$ position angle relative to Earth.
- Observations over multiple epochs are necessary to test whether these features rotate around $\epsilon$ Eridani.
- This study provides valuable insights into planetary formation processes and highlights ALMA's potential for future studies of debris discs around nearby stars.

## Summary

A recent study has revisited the debris disc surrounding $\epsilon$ Eridani, the closest star to our Sun known to host such a disc. Previous observations in the (sub-)millimetre regime had suggested that clumpy structures in the disc were due to interactions with an undetected planet. However, these observations could not distinguish between background confusion and structure in the disc. The new study presents the first ALMA image of the entire disc, with a resolution of 1.6"$\times$1.2", which clearly detects the star, main belt and two point sources. The data's sensitivity allows for clear differentiation between background galaxies (point sources) and disc emission. After accounting for these sources, two clumps with $>3\sigma$ significance remain in the main belt - one to the east of the star and another to its northwest. The authors performed $n$-body simulations that showed how migrating planets can create similar structures by trapping planetesimals in resonances. They found that a migrating planet could reproduce observed features by trapping planetesimals in a 2:1 mean motion resonance, and that symmetry of prominent clumps indicated that such a planet should have either ${\sim10^\circ}$ or ${\sim190^\circ}$ position angle relative to Earth. Observations over multiple epochs are necessary to test whether these features rotate around $\epsilon$ Eridani. This study provides valuable insights into planetary formation processes and highlights ALMA's potential for future studies of debris discs around nearby stars. It demonstrates how powerful tools like ALMA can be used to explore complex systems like debris discs and detect subtle features related to planetary formation processes such as resonances created by migrating planets.