The detection of a potentially rocky world around a nearby star opens up unprecedented prospects for the atmospheric characterization of exoplanets. This discovery, made by an international collaboration, positions a unique celestial object as the prime target for future observational instruments. Its relative proximity to our Solar System makes it an exceptional subject of study for the next generation of telescopes.
The exoplanet GJ 251 c, located just 18 light-years from Earth, represents a particularly promising case in the search for habitable planets. Astronomers have determined that this object has a mass several times greater than that of our planet and orbits squarely within the temperate zone of its host star. These characteristics make it a prime candidate for further investigation into the possible presence of liquid water on its surface.
An international team of scientists, including researchers from Penn State, has described the exoplanet GJ 251 c as a "super-Earth," as data suggest a rocky composition similar to Earth's and a mass almost four times greater.
Credit: Illustration by the University of California, Irvine. Detection via the Doppler effect
The identification of GJ 251 c results from a meticulous analysis of the radial velocity variations of its star. The researchers used data spanning more than two decades of observations, combined with high-precision measurements obtained with the HPF spectrograph. This innovative instrument captures the tiny stellar oscillations induced by the gravitational pull of orbiting planets.
The radial velocity method allowed the exoplanet's signal to be distinguished from the "noise" generated by the star's magnetic activity. Scientists developed computational models to isolate the periodic signature corresponding to a 54-day orbit. This statistical approach confirmed the existence of the celestial body with a high degree of confidence.
The definitive validation of the planet required the complementary use of the NEID spectrometer, demonstrating the importance of instrumental collaborations. These cutting-edge technologies operate in the infrared domain, where stellar disturbances are attenuated. Their unparalleled precision allows the detection of velocity variations of less than a few meters per second.
Prospects for direct observation
The favorable position of GJ 251 c makes it an ideal candidate for direct imaging with the future TMT telescope. The giant mirrors of this observatory, currently under development, will have the angular resolution necessary to distinguish the planet from its host star. This spatial separation will allow the light from each object to be analyzed separately.
Direct observations will pave the way for atmospheric spectroscopy of the exoplanet. Scientists will be able to search for the presence of water vapor, carbon dioxide, or other chemical markers indicative of habitability. Determining the atmospheric composition will be a decisive step in assessing the biological potential of this world.
The astronomical community considers this discovery an important milestone toward planetary characterization missions. The data collected will guide the design of observation programs for the TMT and other world-class observatories. The in-depth study of GJ 251 c could establish new methodological standards for the analysis of temperate exoplanets.
Concretely, why is this planet described as "potentially habitable"?
Three main criteria, deduced from its star and its orbit, allow astronomers to describe GJ 251 c as "potentially habitable."
First, its orbital position lies within the temperate zone of its star, also called the "habitable zone." This is the region where the energy received from the star theoretically allows water to exist in liquid form on a planet's surface, under adequate atmospheric pressure. Liquid water is considered an essential ingredient for life as we know it.
Second, mass data suggest that this planet is most likely rocky, with a solid surface similar to that of Earth, Mars, or Venus. A solid surface is another criterion considered favorable for the emergence and development of life, as opposed to gas giant planets like Jupiter.
Third, its host star, a mature red dwarf named GJ 251, offers a relatively stable environment over very long periods. Unlike young, highly active red dwarfs prone to violent flares, this calmer star provides a setting where a planetary atmosphere could potentially be maintained and allow favorable conditions to persist.
It is important to note that "potentially habitable" does not mean "inhabited." This designation only indicates that the basic physical conditions could be met. The actual presence of liquid water and a suitable atmosphere remains to be confirmed by future observations.
Article author: Cédric DEPOND