A team of astronomers has identified a potentially habitable exoplanet named Gliese 12 b, located approximately 40 light-years away in the constellation Pisces. This exoplanet is slightly smaller than Earth, comparable in size to Venus, and possesses a relatively mild surface temperature.
The discovery was detailed in a study published on May 23 in the Monthly Notices of the Royal Astronomical Society. Shishir Dholakia, a co-author and PhD student at the Southern Queensland University Astrophysics Centre, stated that "Gliese 12 b represents one of the best targets to study whether Earth-sized planets orbiting cool stars can retain their atmospheres, a crucial step in advancing our understanding of habitability in our galaxy."
Gliese 12 b orbits its host star every 12.8 days, with an estimated surface temperature of 42 degrees Celsius. While relatively warm, this temperature is significantly lower than that of most of the approximately 5,000 confirmed exoplanets to date.
Dholakia noted, "Atmospheres trap heat, and depending on their composition, they can substantially alter the actual surface temperature." The planet's "equilibrium temperature" is cited, indicating the temperature it would have without an atmosphere.
The exoplanet could possess two very different atmospheric configurations. An Earth-like atmosphere, composed of oxygen, nitrogen, and other life-friendly elements, would imply the potential for supporting life. Conversely, if Gliese 12 b has a Venus-like atmosphere, it could experience a runaway greenhouse effect, resulting in extremely high surface temperatures.
Learissa Palethorpe, another co-author and PhD student at the University of Edinburgh and University College London, explained that "the early atmospheres of Earth and Venus are thought to have been stripped and then replenished through volcanic outgassing and residual material bombardment in the solar system."
Gliese 12 b, with a temperature between that of Earth and Venus, could provide insights into the pathways of habitability that planets follow as they develop.
This is not the first Earth-like exoplanet discovered; the closest known similar exoplanet is Proxima Centauri b, located just four light-years away. However, since it is not a transiting world, its atmospheric composition and potential for supporting life remain unknown.
Most exoplanets are discovered using the transit method, where astronomers observe a planet passing in front of its star, causing a dip in brightness similar to an eclipse. During this event, the star's light passes through the exoplanet's atmosphere, with some wavelengths absorbed. Different gases absorb distinct wavelengths, leaving chemical fingerprints that instruments like the James Webb Space Telescope (JWST) can identify.
The host star of Gliese 12 b, a red dwarf designated as Gliese 12, is approximately 27% the size of our Sun and has a surface temperature only 60% as warm. It also shows no signs of intense magnetic activity or frequent large X-ray flares, which many red dwarf stars exhibit, raising cautious optimism that Gliese 12 b's atmosphere may remain intact.
Masayuki Kuzuhara, co-author and astrobiologist at the Astrobiology Center in Tokyo, remarked, "Although we still do not know if it has an atmosphere, we have been thinking of it as an exo-Venus, with size and energy received from its star similar to our planetary neighbor in the solar system."
The international research team utilized observations from NASA's Transiting Exoplanet Survey Satellite (TESS) to aid this discovery and plans to use the JWST for further observations of this potential Earth-twin exoplanet.