Using NASA’s Transiting Exoplanet Survey Satellite (TESS) and many other telescopes, two teams of astronomers have discovered a temperate, Earth-sized exoplanet orbiting a cool red dwarf called Gliese 12. Named Gliese 12b, the planet may have an Earth-like atmosphere, one more akin to Venus, no atmosphere, or perhaps a different kind of atmosphere not found in our Solar System.
An artist’s impression of Gliese 12b and its host star. Image credit: NASA / JPL-Caltech / R. Hurt, Caltech-IPAC.
Gliese 12 is a M3-type dwarf star located 12.2 parsecs (40 light-years) away in the constellation of Pisces.
Otherwise known as TOI-6251 or GJ 12, this star is only about 27% of the Sun’s size, with about 60% of the Sun’s surface temperature.
The newly-discovered planet, Gliese 12b, is Earth’s size or slightly smaller — comparable to Venus.
“We’ve found the nearest, transiting, temperate, Earth-size world located to date,” said Dr. Masayuki Kuzuhara, an astronomer at the Astrobiology Center in Tokyo and lead author of a paper published in the Astrophysical Journal Letters.
“Although we don’t yet know whether it possesses an atmosphere, we’ve been thinking of it as an exo-Venus, with similar size and energy received from its star as our planetary neighbor in the Solar System.”
“Gliese 12b represents one of the best targets to study whether Earth-size planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on planets across our Galaxy,” added Shishir Dholakia, a doctoral student at the University of Southern Queensland and lead author of a paper published in the Monthly Notices of the Royal Astronomical Society.
Gliese 12b has an orbital period of 12.76 days and an equilibrium temperature of around 42 degrees Celsius (107 degrees Fahrenheit). For comparison, Earth has an average surface temperature of 15 degrees Celsius (59 degrees Fahrenheit).
The alien world receives 1.6 times more energy from its star as Earth does from the Sun and about 85% of what Venus experiences.
“Atmospheres trap heat and — depending on the type — can change the actual surface temperature substantially,” Dholakia said.
“We are quoting the planet’s equilibrium temperature, which is the temperature the planet would be if it had no atmosphere.”
“Much of the scientific value of this planet is to understand what kind of atmosphere it could have.”
“Since Gliese 12b gets in between the amount of light as Earth and Venus get from the Sun, it will be valuable for bridging the gap between these two planets in our Solar System.”
The astronomers suggest that studying Gliese 12b may help unlock some aspects of our own Solar System’s evolution.
“It is thought that Earth’s and Venus’ first atmospheres were stripped away and then replenished by volcanic outgassing and bombardments from residual material in the Solar System,” said Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London.
“The Earth is habitable, but Venus is not due to its complete loss of water.”
“Because Gliese 12b is between Earth and Venus in temperature, its atmosphere could teach us a lot about the habitability pathways planets take as they develop.”
One important factor in retaining an atmosphere is the storminess of its star. Red dwarfs tend to be magnetically active, resulting in frequent, powerful X-ray flares.
However, analyses by both teams conclude that Gliese 12 shows no signs of extreme behavior.
During a transit, the host star’s light passes through any atmosphere. Different gas molecules absorb different colors, so the transit provides a set of chemical fingerprints that can be detected by telescopes like Webb.
“We know of only a handful of temperate planets similar to Earth that are both close enough to us and meet other criteria needed for this kind of study, called transmission spectroscopy, using current facilities,” said Dr. Michael McElwain, an astrophysicist at NASA’s Goddard Space Flight Center.
“To better understand the diversity of atmospheres and evolutionary outcomes for these planets, we need more examples like Gliese 12b.”
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Masayuki Kuzuhara et al. 2024. Gliese 12b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy. ApJL 967, L21; doi: 10.3847/2041-8213/ad3642
Shishir Dholakia et al. 2024. Gliese 12b, a temperate Earth-sized planet at 12 parsecs discovered with TESS and CHEOPS. MNRAS 531 (1): 1276-1293; doi: 10.1093/mnras/stae1152
