Magnetic fields play a fundamental role in planetary habitability, acting as protective shields. Detecting them on planets outside our solar system has remained a persistent challenge for science.
Now, a study published in the journal Science and led by the Institute of Astrophysics of Andalusia (IAA-CSIC) in Granada presents the most solid evidence to date that an exoplanet can alter its star's behavior. Specifically, it has been observed that GJ 436 b, a Neptune-like exoplanet in close orbit around its star, causes regular changes in the star's brightness and energy emission at certain wavelengths.
Analyzing these variations has allowed the team to estimate, for the first time, the intensity of the magnetic field of such an exoplanet. This breakthrough opens a new frontier for studying the properties and potential habitability of worlds beyond our solar system.
The presence of a planetary magnetic field is crucial for atmospheric evolution and protection against stellar wind, as seen on Earth. Mars's loss of its magnetic field, for instance, contributed to the degradation of its atmosphere.
The research was based on sixteen years of spectroscopic observations of the GJ 436 system. The findings suggest that while stars typically dominate interactions with their planets, a nearby planet can, in turn, influence its star. The interaction between GJ 436 b and its star injects energy into the stellar chromosphere, generating a phenomenon analogous to Earth's auroras.
These interactions have been detected in specific episodes (2008, 2016, 2024), separated by eight-year cycles, coinciding with the star's magnetic activity. Comparison with theoretical models has allowed estimation that GJ 436 b's magnetic field could be between 2.33 and 27 times stronger than Jupiter's.
This discovery is key to understanding exoplanets' ability to retain atmospheres and their potential to harbor life, according to Daniel Revilla, an IAA-CSIC researcher and lead author of the study.
Various Spanish institutions collaborated on the research, including the Center for Astrobiology (CAB), the Institute of Space Studies of Catalonia (IEEC), the Institute of Space Sciences (ICE-CSIC), the Institute of Astrophysics of the Canary Islands (IAC), and the University of the Balearic Islands (UIB), alongside international teams.
