New findings have led researchers to believe that GJ 3378b is more likely a rocky planet than a gas giant. At a distance of only 25 light-years, it has become one of the most attractive targets for studying the possibility of life.
A potentially habitable planet orbiting a red dwarf star (Illustrative image: M. Kornmesser).
GJ 3378b belongs to the group of "super-Earths"—planets larger than Earth, which are of particular interest to scientists in the search for extraterrestrial life.
According to research published in The Astrophysical Journal , a team of authors led by astronomer Paul Robertson (University of California, Irvine, USA) stated: "GJ 3378b is one of the most Earth-like exoplanets ever known within 10 parsecs (approximately 32.6 light-years) of the Solar System."
According to Robertson, compared to the Milky Way's diameter of approximately 100,000 light-years, a distance of 25 light-years is almost like being a next-door neighbor.
Criteria for finding a "second Earth"
Besides Earth, where else in the universe does life exist? Modern astronomy is still searching for an answer to this question.
Scientists are trying to determine the conditions that make a planet suitable for life, from the type of star it orbits and the structure of its planetary system to its atmosphere.
However, the "habitable zone" is always the first criterion scientists consider before evaluating more complex conditions.
This is the ideal distance between the planet and its host star, where the temperature allows water to exist in liquid form on its surface. If the planet is too close to the star, the water will evaporate, or if it is too far away, the water will freeze.
The TRAPPIST-1 system consists of 7 exoplanets orbiting a red dwarf star (Image: NASA).
"All known forms of life on Earth need water, so this has always been the first priority," Robertson said.
To date, Earth remains the only planet confirmed to harbor life. Therefore, when screening candidates for further study, scientists often prioritize rocky planets – conditions similar to Earth.
Why is GJ 3378b special?
Since its discovery in 2024, GJ 3378b has attracted attention because its orbital period around its host star is approximately 24.73 days, placing it within the habitable zone around a red dwarf star.
However, the mass of GJ 3378b remains unknown. In exoplanet research, a mass of approximately five times that of Earth is considered a relative boundary to distinguish between two groups of planets with different characteristics.
Planets smaller than this threshold are typically super-Earths with rocky surfaces, while much larger planets are more likely to be mini-Neptunes, surrounded by thick atmospheres.
Initial estimates suggest that GJ 3378b has a mass of about 5.3 times that of Earth, placing it right on the boundary between the two groups.
Graphic simulating the view that can be observed from the surface of planet GJ 3378b (Image: Nikolai Berman).
To clarify this, the research team used multiple telescopes on the ground and in space to observe the very small oscillations of the star caused by the planet's gravitational pull.
"To detect small-mass planets, we need to find extremely weak signals. If the observation equipment isn't accurate enough, we won't be able to detect them," said astronomer Michael Endl (University of Texas at Austin).
The new measurements allowed the research team to more precisely determine the orbit and mass of GJ 3378b.
This planet actually takes only 21.45 days to complete one orbit around its host star, shorter than initially estimated, and still firmly within the habitable zone.
"This super-Earth receives about 90% of the radiation from its host star compared to the amount Earth receives from the Sun. It's exactly within the ideal range of conditions," Robertson said.
More importantly, the mass was adjusted down to 2.3 times the mass of Earth, reinforcing the possibility that it is a rocky planet.
However, that doesn't necessarily mean the planet is habitable.
To maintain liquid water on its surface, a planet must possess an atmosphere. Scientists currently do not know whether GJ 3378b has this condition.
In addition, red dwarf stars are often more active than the Sun, constantly producing bursts of energy and coronal mass ejections, which can strip the atmospheres of nearby orbiting planets.
Nevertheless, with the latest data, GJ 3378b has emerged as one of the leading candidates for studying the possibility of life existing outside the Solar System.
The relative size between GJ 3378b and Earth (Image: NASA).
"GJ 3378b takes us one step further in understanding our Solar System neighbors and identifying which planets might be suitable for life," Endl shared.