Effects of stellar magnetism could expand criteria for exoplanet habitability

Curiosity in Earth-like planets orbiting throughout the liveable zone of their host stars has surged, pushed by the search to find life past our solar system. However the habitability of such planets, generally known as exoplanets, is influenced by extra than simply their distance from the star.

A brand new examine by Rice College’s David Alexander and Anthony Atkinson extends the definition of a liveable zone for planets to incorporate their star’s magnetic field. This issue, properly studied in our solar system, can have important implications for all times on different planets, in line with the analysis printed in The Astrophysical Journal on July 9.

The presence and power of a planet’s magnetic area and its interplay with the host star’s magnetic area are pivotal elements in a planet’s means to assist life. An exoplanet wants a robust magnetic area to guard it from stellar activity, and it should orbit far sufficient from its star to keep away from a direct and probably catastrophic magnetic connection.

“The fascination with exoplanets stems from our want to know our personal planet higher,” mentioned Alexander, professor of physics and astronomy, director of the Rice Area Institute and member of the Texas Aerospace Analysis and Area Financial system Consortium. “Questions concerning the Earth’s formation and habitability are the important thing drivers behind our examine of those distant worlds.”

Magnetic interactions

Historically, scientists have targeted on the “Goldilocks Zone,” the realm round a star the place situations are excellent for liquid water to exist. By including the star’s magnetic area to the habitability standards, Alexander’s group provides a extra nuanced understanding of the place life would possibly thrive within the universe.

The investigation targeted on the magnetic interactions between planets and their host stars, an idea generally known as space climate. On Earth, space climate is pushed by the sun and impacts our planet’s magnetic area and environment. For the examine, the researchers simplified the complicated modeling normally required to know these interactions.

The researchers characterised stellar exercise utilizing a measure of a star’s exercise generally known as the Rossby quantity (Ro): the ratio of the star’s rotation interval to its convective turnover time. This helped them estimate the star’s Alfvén radius—the gap at which the stellar wind successfully turns into decoupled from the star.

Planets inside this radius wouldn’t be viable candidates for habitability as a result of they might be magnetically related again to the star, resulting in fast erosion of their environment.

By making use of this strategy, the group examined 1,546 exoplanets to find out if their orbits lay inside or exterior their star’s Alfvén radius.

Life elsewhere within the galaxy

The examine discovered that solely two planets, K2-3 d and Kepler-186 f, of the 1,546 examined met all of the situations for potential habitability. These planets are Earth-sized, orbit at a distance conducive to the formation of liquid water, lie exterior their star’s Alfvén radius and have robust sufficient magnetic fields to guard them from stellar exercise.

“Whereas these situations are needed for a planet to host life, they don’t assure it,” mentioned Atkinson, a graduate pupil of physics and astronomy and lead writer of the examine. “Our work highlights the significance of contemplating a variety of things when trying to find liveable planets.”

The examine additionally underscores the necessity for continued exploration and statement of exoplanetary methods, drawing classes from the sun-Earth system. By increasing the standards for habitability, the researchers present a framework for future research and observations to work towards figuring out whether or not we’re alone within the universe.

Alison Farrish, a postdoctoral researcher on the NASA Goddard Area Flight Heart and former Rice graduate pupil, can also be an writer of this examine.