Astronomers have discovered a super-Earth exoplanet, GJ 251 c, just 20 light-years from Earth, orbiting in its star's habitable zone. The planet, nearly four times Earth's mass and likely rocky, offers one of the best chances yet to search for signs of life beyond our solar system. The finding stems from over two decades of observations using advanced telescopes led by Penn State researchers.
The exoplanet GJ 251 c was identified through meticulous analysis of stellar wobbles detected over more than 20 years by telescopes worldwide. Located in the 'Goldilocks Zone' of its host star, GJ 251, the planet is at a distance where liquid water could exist on its surface, assuming the right atmosphere.
"We look for these types of planets because they are our best chance at finding life elsewhere," said Suvrath Mahadevan, the Verne M. Willaman Professor of Astronomy at Penn State and co-author of a paper in The Astronomical Journal. The discovery relied on the Habitable-Zone Planet Finder (HPF), a near-infrared spectrograph designed and built by Penn State researchers and installed on the Hobby-Eberly Telescope at McDonald Observatory in Texas. Confirmation came from the NEID spectrometer at Kitt Peak National Observatory in Arizona.
The team refined data on the inner planet, GJ 251 b, which orbits every 14 days, and detected a new signal repeating every 54 days, indicating GJ 251 c's presence. Challenges included distinguishing planetary signals from the star's magnetic activity, likened by Mahadevan to 'stellar weather.' Advanced modeling across different light wavelengths helped overcome this.
"This discovery represents one of the best candidates in the search for atmospheric signature of life elsewhere in the next five to ten years," Mahadevan added. Corey Beard, the paper's corresponding author, emphasized the cutting-edge technology: "We are at the cutting edge of technology and analysis methods with this system."
Eric Ford, distinguished professor at Penn State, highlighted the multi-disciplinary effort: "The combination of exquisite data and state-of-the-art statistical methods enabled our interdisciplinary team to transform data into an exciting discovery."
While direct imaging is not yet possible, future 30-meter-class telescopes could analyze GJ 251 c's atmosphere for life traces. The research was supported by the U.S. National Science Foundation, NASA, and the Heising-Simons Foundation. The findings appear in The Astronomical Journal (2025; 170(5): 279).