Telescopio Nazionale Galileo Leads the Discovery of a Super-Earth in the Habitable Zone of a Nearby Red Dwarf

An international team of astronomers, using the HARPS-N spectrograph on the Telescopio Nazionale Galileo (TNG) at Roque de los Muchachos Observatory, La Palma, has made a groundbreaking discovery: a new super-Earth orbiting in the habitable zone of the nearby red dwarf star GJ 3998, located just 59 light-years away. This planet, named GJ 3998 d, is the third planet found in this system, further highlighting the critical role of the TNG in advancing the search for exoplanets.

The discovery underscores the importance of the TNG and its HARPS-N instrument in the ongoing effort to explore planetary systems around red dwarfs, stars that are abundant in our galaxy but still hold many secrets. The fact that GJ 3998 d resides in the habitable zone of one of our nearest stellar neighbours brings us one step closer to understanding where habitable planets may exist in our cosmic backyard.

The newly discovered GJ 3998 d has a mass six times that of Earth and orbits its star every 41.8 days. Positioned in the habitable zone of its cooler and smaller star, the planet receives just 20% more stellar irradiation than Earth. Despite differences in the star’s size and temperature, if the planet is rocky, it could potentially host liquid water—a key ingredient for life.

This discovery is part of the HADES program, an international collaboration dedicated to investigating planetary systems around red dwarfs using the TNG. Red dwarfs, which make up nearly three-quarters of the stars in our galaxy, are prime targets in the hunt for low-mass planets due to their abundance and relative proximity.

Previously, in 2016, the same team had already detected two planets orbiting GJ 3998. The recent discovery of GJ 3998 d was made possible by ongoing observations using the HARPS-N spectrograph at the TNG, which allowed the team to detect the small shifts in the star’s position caused by the gravitational influence of orbiting planets.

"In the 2016 discovery, the period we now associate with the third planet was originally attributed to the star's differential rotation. The data available at the time led us to this conclusion,” explains Laura Affer (INAF). "To better understand whether this period could be linked to a planet, we kept monitoring the radial velocity of the star with HARPS-N, dedicating a significant portion of our observing time to this object. With the new data available, we were finally able to confirm the planetary nature of the signal.”

This discovery further demonstrates that multi-planet systems are more common than previously thought, with new data and techniques often revealing planets that were missed in earlier observations. ‘Planets, in particular low-mass ones, are rarely on their own — they prefer to have company. Often, when we revisit a system with new measurements and new methods, we find new planets that had been overlooked before’, concludes Atanas Stefanov, leading author of the paper.

Atanas Stefanov, et al. "A super-Earth in the habitable zone of the GJ 3998 multi-planetary system",
Astronomy & Astrophysics, 2025. (DOI)

Recreation of the planet GJ 3998 d and its orbit. Credit: Gabriel Pérez Díaz (SMM, IAC)

Artist's impression of GJ 3998 d, a super-Earth in the habitable zone of its star. Credit: Gabriel Pérez Díaz (SMM, IAC)