Intriguing Earth-sized world found independently by two groups of astronomers

• Gliese 12 b is the name of the new exoplanet, the nearest, transiting, temperate, Earth-size world located to date
• The planet is a unique candidate for further atmospheric study that may help unlock some aspects of our own solar system’s evolution
• IEEC researchers at the Institute of Space Sciences have participated in this study

Two international teams of astronomers have discovered an exciting planet between the sizes of Earth and Venus only 40 light-years away. Multiple factors make it one of the highest-profile worlds for further study using the James Webb Space Telescope of NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). Researchers from the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) at the Institute of Space Sciences (ICE-CSIC) have participated in this research with one of the teams, whose results appear in The Astrophysical Journal Letters.

Gliese 12 b is the name of the new exoplanet, discovered by an international team led by scientists from the Astrobiology Center in Japan, the University of Tokyo, the National Astronomical Observatory of Japan, and Tokyo Institute of Technology through a collaboration between NASA’s TESS (Transiting Exoplanet Survey Satellite) campaign and a strategic survey programme (SSP) of the Subaru Telescope. Capturing transits—brief, regular dimmings of stars caused by the passage of orbiting worlds—is one of the most common methods to detect exoplanets.

“We’ve found the nearest, transiting, temperate, Earth-size world located to date,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, who co-led one research team with Akihiko Fukui, a project assistant professor at the University of Tokyo. “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 neighbour in the solar system.”

Detecting a new world

The host star, called Gliese 12, is a cool red dwarf located almost 40 light-years away in the constellation Pisces. The star is only about 27% of the Sun’s size, with about 60% of the Sun’s surface temperature. The TESS team detected signs of a planet candidate with a size similar to Earth and reported the detection in April, 2023. This report motivated the astronomers to start the follow-up observations for validating the candidate signal with multi-colour cameras developed by the Astrobiology Center (ABC) and the University of Tokyo. 

Juan Carlos Morales and Ignasi Ribas, both IEEC researchers at the ICE-CSIC, have collaborated with the Japanese team. “We were able to constrain the mass of the planet to be less than 3.9 Earth masses by combining measurements taken with Subaru and those with CARMENES on the 3.5 m telescope of the Calar Alto Observatory,” explains Juan Carlos Morales.

The new world, Gliese 12 b, orbits every 12.8 days and is Earth’s size or slightly smaller—comparable to Venus. Assuming it has no atmosphere, the planet has a surface temperature estimated at around 42 ºC.

The diminutive sizes and masses of red dwarf stars make them ideal for finding Earth-size planets. A smaller star means a greater decrease in brightness each time a planet passes in front of it and a smaller mass means that an orbiting planet can produce a greater wobble, known as “reflex motion”, of the star. These effects make smaller planets easier to detect. 

The lower luminosities of red dwarf stars also means their habitable zones—the range of orbital distances where liquid water could exist on a planet’s surface—lie closer to them. This makes it easier to detect transiting planets within habitable zones around red dwarfs than those around stars emitting more energy.

A great candidate for atmospheric study

The distance separating Gliese 12 and the new planet is just 7% of the distance between Earth and the Sun. The planet receives 1.6 times more energy from its star as Earth does from the Sun and about 85% of what Venus experiences. 

“Gliese 12 b 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,” said Shishir Dholakia, a doctoral student at the Centre for Astrophysics at the University of Southern Queensland in Australia. He co-led a different research team with Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London.

Caption: Gliese 12 b’s estimated size may be as large as Earth or slightly smaller—comparable to Venus in our solar system. This artist’s concept compares Earth with different possible Gliese 12 b interpretations, from no atmosphere to a thick Venus-like one. Follow-up observations with the James Webb Space Telescope will help determine just how much atmosphere the planet retains as well as its composition.
Credits: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC).

“This is a unique candidate for further atmospheric study that may help unlock some aspects of our own solar system’s evolution,” Palethorpe explained. “Earth remains habitable, but Venus does not due to its complete loss of water. Gliese 12 b’s 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 behaviour, which could help preserve the planet’s atmosphere.

During a transit, the host star’s light passes through any atmosphere, effectively sampling it. Different gas molecules absorb different colours, so the transit provides a set of chemical fingerprints that can be detected by telescopes like Webb.  

“We know of only a handful of systems to date that are both close enough to us and meet other criteria needed for this kind of study, called transmission spectroscopy, using current facilities,” said Michael McElwain, a research astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a co-author of the Kuzuhara paper. “To better understand the diversity of atmospheres around temperate planets similar to Earth, we need more examples like Gliese 12 b,” he concludes.

More information

This research is presented in a paper entitled “Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy”, by Masayuki Kuzuhara, Akihiko Fukui et al. (including Juan Carlos Morales and Ignasi Ribas), which has appeared in the journal The Astrophysical Journal Letters on 23 May 2024.

The Dholakia and Palethorpe findings were published in Monthly Notices of the Royal Astronomical Society on the same day.

Links

• IEEC
• ICE-CSIC
• CARMENES
• Subaru Telescope
• TESS

Contacts

About the IEEC

The Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of more than 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centres, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.

The IEEC is a non-profit public sector foundation that was established in February 1996. It has a Board of Trustees composed of the Generalitat de Catalunya, Universitat de Barcelona (UB), Universitat Autònoma de Barcelona (UAB), Universitat Politècnica de Catalunya · BarcelonaTech (UPC), and the Spanish Research Council (CSIC). The IEEC is also a CERCA centre.