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Our Inhabited Heliosphere: The Implications of Stellar Motion through Galactic Interstellar Clouds On Planetary Atmospheres

Presentation #1215 in the session “Open Engagement Session C”.

Published onMar 17, 2021
Our Inhabited Heliosphere: The Implications of Stellar Motion through Galactic Interstellar Clouds On Planetary Atmospheres

The Sun is currently moving through a rich and complex suite of partially ionized, warm, interstellar clouds. An interface, dictated by pressure balance, magnetic fields, and charge exchange, signifies the interaction between a outward moving stellar wind and the inward force of the surrounding local interstellar medium (LISM). As stars and the ISM each comprise roughly half of the luminous matter in galaxies, these interactions are ubiquitous. The interaction is also dynamic. While stellar wind strengths change slowly, at least during the main sequence, the density of interstellar clouds ranges by more than six orders of magnitude. The implication is that the solar heliosphere and stellar astrospheres are permanent features of planetary systems and are constantly changing. The stellar magnetic field and particle interactions can lead to a filtering of low and high-energy (i.e., cosmic rays) particles. The particles that make it through the filter can be deposited in the atmospheres and on the surfaces of planets in the system. Therefore, the galactic interstellar environment, and the resulting interface with the star, can potentially have an influence on the habitability of a planet. This is a refined and planetary system specific version of the galactic habitable zone paradigm. I will discuss work to measure and model the morphology and physical properties of the LISM. These clouds reside in our immediate cosmic neighborhood, within 20 pc. This same volume contains several detected astrospheres and the nearest and most favorable exoplanetary systems with planets in habitable zone orbits. I will also discuss the the influence the LISM has on observations to characterize the atmospheres of exoplanets. Finally, I will present results of a project to observe the interstellar environment that the Sun traversed in its most recent past (e.g., within the last 5 Myr) and evaluate the corresponding impact on our historical heliosphere. While perhaps not a primary driver of habitability in general, it is worth exploring the impact of these planetary system-ISM interactions, and identifying extreme systems where it may have a significant influence on habitability.

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