# The Threatening Environment of the TRAPPIST-1 Planets

## TL;DR

This study uses advanced 3D models to analyze the stellar wind environment of the TRAPPIST-1 planets, revealing extreme conditions that threaten their atmospheres and potential habitability.

## Contribution

It provides the first detailed 3D magnetohydrodynamic simulations of stellar wind interactions with all TRAPPIST-1 planets, highlighting their vulnerability to atmospheric erosion.

## Key findings

- All planets experience stellar wind pressures 1000 to 100,000 times Earth's.
- Most planets spend significant time in sub-Alfvénic conditions.
- Planetary magnetic fields are highly compressed and dynamic.

## Abstract

Recently, four additional Earth-mass planets were discovered orbiting the nearby ultracool M8 dwarf TRAPPIST-1, making a remarkable total of seven planets with equilibrium temperatures compatible with the presence of liquid water on their surface. Temperate terrestrial planets around an M-dwarf orbit close to their parent star, rendering their atmospheres vulnerable to erosion by the stellar wind and energetic electromagnetic and particle radiation. Here, we use state-of-the-art 3D magnetohydrodynamic models to simulate the wind around TRAPPIST-1 and study the conditions at each planetary orbit. All planets experience a stellar wind pressure between $10^3$ and $10^5$ times the solar wind pressure on Earth. All orbits pass through wind pressure changes of an order of magnitude and most planets spend a large fraction of their orbital period in the sub-Alfv\'enic regime. For plausible planetary magnetic field strengths, all magnetospheres are greatly compressed and undergo much more dynamic change than that of the Earth. The planetary magnetic fields connect with the stellar radial field over much of the planetary surface, allowing direct flow of stellar wind particles onto the planetary atmosphere. These conditions could result in strong atmospheric stripping and evaporation and should be taken into account for any realistic assessment of the evolution and habitability of the TRAPPIST-1 planets.