English (UK)
 |
| Artist's illustration of the interaction star (GJ 436) - exoplanet (GJ 436 b). Credits: IAA-CSIC/LampScience |
Almeria, June 29th, 2026
An international team led by the Institute of Astrophysics of Andalusia (IAA-CSIC) has provided the first conclusive evidence of a planet’s influence on the behavior of its star. Observations conducted largely with the CARMENES instrument at Calar Alto Observatory have made it possible to detect and estimate the strength of the magnetic field of the exoplanet GJ 436 b, opening a new avenue for studying the habitability of planets outside the Solar System.
Magnetic fields play a fundamental role in the habitability of planets. On Earth, the magnetic field acts as a shield against the solar wind and contributes to the evolution of its atmosphere—a key condition for the existence of life. However, detecting and measuring these magnetic fields on planets outside the Solar System remains one of the great challenges of astronomy.
A study just published in the Science journal and led by the Institute of Astrophysics of Andalusia (IAA-CSIC) demonstrates, conclusively for the first time, that a planet can directly influence the behavior of its star. This finding provides the strongest evidence to date for the existence of a magnetic field on an exoplanet.
“In particular, we have observed that GJ 436 b, a Neptune-like exoplanet that orbits very close to its star, causes regular changes in the star’s brightness and the energy it emits at certain wavelengths,” explains Daniel Revilla, a researcher at IAA-CSIC who is leading the study as part of his doctoral thesis.
Furthermore, by analyzing how and when these variations in the star occur, the team was able to estimate, for the first time, the strength of the magnetic field of a planet of this type, opening a new avenue for studying the properties and habitability of worlds beyond the Solar System.
MAGNETIC FIELDS BEYOND THE SOLAR SYSTEM
The presence of a magnetic field can influence a planet’s evolution, since, by modulating the interaction between the stellar wind and the planetary atmosphere, it affects processes related to its habitability. Earth is an example of this. Mars, on the other hand, lost its intense global magnetic field billions of years ago, which contributed to the gradual loss of its atmosphere and, with it, much of the water it once harbored.
Determining whether exoplanets possess magnetic fields is therefore key to assessing their potential habitability.
 |
| Artist's illustration of Jupiter's magnetic field and the planet–satellite interaction. Credits: IAA-CSIC/LampScience |
In this context, the study led from IAA-CSIC has analyzed sixteen years of high-resolution spectroscopic observations of the GJ 436 system, a low-mass star around which GJ 436 b orbits—a Neptune-like planet that orbits very close to its star. The results provide new insights into the presence of magnetic fields on worlds beyond the Solar System.
“Until recently, it was thought that it was primarily the star that influenced the planet, but our results provide the clearest evidence to date of something that had already been suspected: that the opposite can also occur, and that a close-orbiting planet can alter its star’s environment,” notes Rafael Luque, a researcher at IAA-CSIC who participated in the study.
The results show that, although stars typically dominate the relationship with their planets through their gravity, radiation, and magnetic field, a planet orbiting very close to its star can also influence it. In the case of GJ 436 b, this interaction leaves observable signs that have allowed scientists to infer the existence and strength of its magnetic field.
The observations, obtained with the CARMENES spectrograph at Calar Alto and the HARPS spectrograph in Chile, reveal that GJ 436 b’s magnetic field interacts with that of its star and injects energy into the chromosphere—one of the upper layers of its atmosphere—increasing its activity. This process generates phenomena similar to the auroras (Northern or Southern lights) on Earth, but on a stellar scale.
A KEY PERIOD
The interaction between the planet and the star is not observed continuously. The phenomenon has only been detected in 2008, 2016, and 2024—three episodes separated by eight-year intervals. This periodicity coincides with GJ 436’s magnetic activity cycle, suggesting that the interaction becomes particularly intense—or easier to detect—when the star goes through certain phases of its magnetic cycle.
Comparing these observations with theoretical models has allowed the team to estimate a property that is extremely difficult to measure in an exoplanet: the strength of its magnetic field. “Despite its smaller size, GJ 436 b would have a magnetic field between 2.33 and 27 times stronger than Jupiter’s,” notes Pedro J. Amado, co-author of the study and a researcher at IAA-CSIC.
This result opens a unique opportunity to study the magnetic fields of planets outside the Solar System. Analyzing them provides a better understanding of how they retain their atmospheres, what their internal structure is like, and how they evolve over time.
“Until now, measuring an exoplanet’s magnetic field was extremely difficult. This property is key to determining whether a planet can protect its atmosphere and, ultimately, whether it could potentially support life,” concludes Daniel Revilla.
REFERENCES:
‘Planet-induced Modulation of Stellar Activity in GJ 436: A Look into a Warm Neptune’s Magnetism’
https://doi.org/10.1126/science.adv3075
MORE INFORMATION:
- Daniel Revilla -
This email address is being protected from spambots. You need JavaScript enabled to view it. - Pedro J. Amado -
This email address is being protected from spambots. You need JavaScript enabled to view it. - Rafael Luque -
This email address is being protected from spambots. You need JavaScript enabled to view it.
COMMUNICATION- CALAR ALTO OBSERVATORY
This email address is being protected from spambots. You need JavaScript enabled to view it. - Phone: (+34) 950 632 500
The Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on March 11th, 2022, by the Science, Technology and Innovation Policy Council (CPCTI).
