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Published October 23, 2025 | Version v1
Technical Report Open

The Exospace Weather Frontier

Creators

  • 1. ROR icon Eureka Scientific
  • 2. ROR icon Arizona State University
  • 3. California Institute of Technology
  • 4. ROR icon Jet Propulsion Lab
  • 5. ROR icon Leibniz Institute for Astrophysics Potsdam
  • 6. ROR icon Goddard Space Flight Center
  • 7. ROR icon University of Colorado Boulder
  • 8. ROR icon New Jersey Institute of Technology
  • 9. ROR icon Northwest Research Associates
  • 10. ROR icon Johns Hopkins University Applied Physics Laboratory
  • 11. ROR icon Langley Research Center
  • 12. ROR icon National Aeronautics and Space Administration
  • 13. University of Hawai'i
  • 14. ROR icon Lockheed Martin (United States)
  • 15. ROR icon University of California, Santa Cruz
  • 16. ROR icon National Astronomical Observatory of Japan
  • 17. ROR icon Space Telescope Science Institute
  • 18. Universidad Nacional Autónoma de México
  • 19. ROR icon University of Graz
  • 20. ROR icon Leiden University
  • 21. ROR icon High Altitude Observatory
  • 22. ROR icon Peking University

Abstract

Space weather is among the most powerful and least understood forces shaping planetary atmospheres.

We observe its effects directly on Solar System bodies through atmospheric escape, chemical disruption,

cometary tails, and auroral displays. Yet for exoplanets, we lack the tools and data to robustly assess

how space weather influences their evolution, habitability, and potential biosignatures. Even the past

space weather of the Solar System is shrouded in unknowns.

The Sun emits a constant outflow of charged particles embedded in magnetic fields, known as the

solar wind. The fast-moving particles in the winds of the Sun and stars can erode planetary atmospheres

over time, stripping away volatiles essential for climate and life. Potentially even more disruptive are

explosive events, such as flares and coronal mass ejections (CMEs), which hurl vast amounts of energy

and particles into space. Collectively, these phenomena define the space weather environment, and for

our Sun, they are continuously tracked by a fleet of dedicated spacecraft.

Decades of observations reveal that space weather is not unique to the Sun, but is ubiquitous

among stars. Many stars exhibit “exospace weather” through flaring activity, sometimes by orders of

magnitude more intense than anything seen from the Sun. These stars must then also host stellar winds

and many likely produce CMEs.

The study of exospace weather sits at the intersection of heliophysics, planetary science, astro-

physics, and astrobiology. Observing space weather in exoplanetary systems, in combination with

the beautifully resolved, in-situ context of our own system, is necessary to illuminate how stars and

planets evolve, interact with their environments, and shape the conditions for life. Doing so will benefit

heliophysics, planetary science, astrophysics, and astrobiology alike.

The time has come to establish exospace weather as a new pillar of exoplanet and stellar research,

one that bridges stellar physics, planetary evolution, and the search for life beyond Earth. The science

gaps are clear, and many of the tools to close them already exist or can be developed. What is needed

now are coordinated, interdisciplinary research efforts.

Acknowledgement

The “Blazing Paths to Observing Stellar and Exoplanet Particle Environments” study was made

possible by the W. M. Keck Institute for Space Studies, and by the Jet Propulsion Laboratory, California

Institute of Technology, under contract with the National Aeronautics and Space Administration.

The study leads gratefully acknowledge the outstanding support of Harriett Brettle, Executive

Director of the Keck Institute for Space Studies, as well as her dedicated staff, who made the study

experience invigorating and enormously productive. Many thanks are also due to Bethany Ehlmann

and the KISS Steering Committee for seeing the potential of our study concept and selecting it.

We thank all of the workshop participants for their time, enthusiasm, and contributions to the

workshop and this report. The workshop was a memorable experience and set the stage for fruitful

collaborations between people who would likely not have crossed paths were it not for the Keck

Institute for Space Studies.

We thank study participant James Mason for creating a theme song for this workshop.

We thank Yu-Chia Lin for her review of the calculations regarding stellar coronagraphy.

The content of this document is to be considered pre-decisional information and intended for

planning and discussion purposes only.

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