Discovery of a potentially habitable “exo-Venus” with a temperature similar to that of Earth

Astronomers have made the rare and tantalizing discovery of an Earth-like exoplanet, located 40 light-years away, that could be only slightly warmer than our own world. The new paper “Gliese 12 b, A Temperate Earth-sized Planet at 12 Parsecs Discovered with TESS and CHEOPS”, was published in the Monthly Notices of the Royal Astronomical Society.

The potentially habitable planet, named Gliese 12 b, orbits its host star every 12.8 days, is comparable in size to Venus, therefore slightly smaller than Earth, and has an estimated surface temperature of 42°C ( 107°F), which is lower. than most of the approximately 5,000 exoplanets confirmed so far.

This, however, assumes that there is no atmosphere, which is the next crucial step in determining whether it is habitable. It may have an Earth-like atmosphere, closer to that of Venus – which experienced a runaway greenhouse effect that made it a 400°C (752°F) hell – no atmosphere , or perhaps a different type of atmosphere not found in our solar planet. system.

Getting an answer is vital because it would reveal whether Gliese 12 b can maintain temperatures suitable for liquid water – and possibly life – to exist on its surface, while also revealing answers about how and why Earth and Venus have evolved so differently.

Gliese 12 b is by no means the first Earth-like exoplanet to have been discovered, but as NASA has said, only a handful of similar worlds are worth a closer look.

It has been billed as “the closest transiting, temperate, Earth-sized world located to date” and a potential target for further investigation by the James Webb Space Telescope.

The closest – and perhaps most famous – Earth-like exoplanet to us is Proxima Centauri b, located just four light years away. However, as it is not a transiting world, we still have much to learn about it, including whether it has an atmosphere and potential to support life.

Most exoplanets are discovered using the transit method, where a planet passes in front of its star from our perspective, causing the host star to dim in brightness.

During a transit, light from the star also passes through an exoplanet’s atmosphere and certain wavelengths are absorbed. Different gas molecules absorb different colors, so the transit provides a set of chemical fingerprints that can be detected by telescopes like Webb.

Gliese 12 b could also be important because it could help determine whether the majority of stars in our Milky Way galaxy, i.e. cool stars, are capable of hosting temperate planets with atmospheres. and therefore habitable.

It orbits a cool red dwarf star called Gliese 12, located nearly 40 light years from Earth in the constellation Pisces.

“Gliese 12 b represents one of the best targets for studying whether Earth-sized planets orbiting cool stars can retain their atmospheres, a crucial step in advancing our understanding of the habitability of planets in our galaxy,” said Shishir Dholakia, a doctoral student at the Institute. Center for Astrophysics at the University of Southern Queensland in Australia.

He co-led a research team with Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London.

The exoplanet’s host star is about 27% the size of our sun and has a surface temperature that is about 60% that of our own star.

However, the distance between Gliese 12 and the new planet is only 7% of the distance between Earth and the Sun. Gliese 12 b therefore receives 1.6 times more energy from its star than Earth does from the sun and about 85% of what Venus experiences.

This difference in solar radiation is important because it means that the temperature on the planet’s surface depends strongly on atmospheric conditions. Compared to Gliese 12 b’s estimated surface temperature of 42°C (107°F), Earth has an average surface temperature of 15°C (59°F).

“Atmospheres trap heat and, depending on their type, can significantly change the actual surface temperature,” Dholakia explained. “We cite 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 lies in understanding what kind of atmosphere it might have. Since Gliese 12 b falls between the amount of light Earth and Venus receive from the sun, it will be valuable for bridge the gap between these two planets in our solar system.

Palethorpe added: “The early atmospheres of Earth and Venus are thought to have been destroyed and then replenished by volcanic outgassing and bombardment of residual material in the solar system.

“Earth is habitable, but Venus is not due to its complete loss of water. As Gliese 12 b lies between Earth and Venus in temperature, its atmosphere could teach us a lot about pathways to habitability taken by the planets as they develop.”

The researchers, along with another team from Tokyo, used observations from NASA’s Transiting Exoplanet Survey Satellite (TESS) to contribute to their discovery.

“We have found the closest transit, temperate, Earth-sized world to date,” said Masayuki Kuzuhara, project assistant professor at the Tokyo Astrobiology Center, who co-led a research team with Akihiko Fukui, project assistant. professor at the University of Tokyo.

“Although we do not yet know whether it has an atmosphere, we consider it to be an exo-Venus, with a similar size and energy received from its star as our planetary neighbor in the Solar System.”

An important factor in maintaining an atmosphere is the storminess of its star. Red dwarfs tend to be magnetically active, leading to frequent and powerful X-ray flares.

However, analyzes from both teams conclude that Gliese 12 shows no signs of such extreme behavior, giving hope that the atmosphere of Gliese 12 b is still intact.

“We know of only a handful of temperate planets similar to Earth that are both close enough to us and meet other criteria necessary for this type 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 co-author of the Kuzuhara and Fukui paper.

“To better understand the diversity of atmospheres and the evolutionary outcomes of these planets, we need more examples like Gliese 12 b.”

At 40 light years from Earth, Gliese 12 b is approximately the same distance as the TRAPPIST-1 system.

This is made up of seven planets, all about the size of Earth and probably rocky, orbiting a red dwarf star.

Three of them are in the habitable zone, but at least two – and probably all – have no atmosphere and are probably sterile, thus rejecting the hope, when they were discovered eight years ago, that They could be aquatic worlds harboring life.