Potentially habitable ‘exo-Venus’ with Earth-like temperature discovered

Astronomers have made the rare and tantalizing discovery of an Earth-like exoplanet 40 light-years away, which may be just a little warmer than our own world. The new paper “Gliese 12 b, A Temperate Earth-sized Planet at 12 Parsecs Discovered with TESS and CHEOPS” has been published in the Monthly notices of the Royal Astronomical Society.

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

However, that assumes there is no atmosphere, which is the crucial next step in determining whether it is habitable. It could have an Earth-like atmosphere, one more like that of Venus – which experienced a runaway greenhouse effect that turned it into a 400°C (752°F) hellhole – no atmosphere, or perhaps some other kind of atmosphere that does not occur in our solar energy. system.

Getting an answer is critical because it would reveal whether Gliese 12 b can maintain temperatures suitable for liquid water (and possibly life) on its surface, while also unlocking answers about how and why Earth and Venus are so different have evolved.

Gliese 12 b is certainly not the first Earth-like exoplanet to be discovered, but as NASA has said, there are only a handful of similar worlds that warrant a closer look.

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

The closest Earth-like exoplanet – and possibly the best known – is Proxima Centauri b, which is just four light-years away. However, because it is not a moving world, we still have a lot to learn about it, including whether it has an atmosphere and the potential to harbor life.

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

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

Gliese 12 b could also be important because it could help reveal whether the majority of stars in our Milky Way Galaxy – that is, cool stars – are capable of hosting temperate planets that have atmospheres and are therefore habitable.

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

“Gliese 12 b is one of the best targets to study whether Earth-sized planets orbiting cool stars can maintain their atmospheres, a crucial step in advancing our understanding of the habitability of planets in our Milky Way,” says Shishir Dholakia, a PhD candidate at the Center for Astrophysics at the University of Southern Queensland in Australia.

He led a research team together with Larissa Palethorpe, a PhD candidate 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 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 receives from the Sun, and about 85% of what Venus experiences.

This difference in solar radiation is important because it means that the planet’s surface temperature is highly dependent on atmospheric conditions. For comparison 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 the type – can significantly change the actual surface temperature,” Dholakia explains. “We quote the planet’s ‘equilibrium temperature’, which is the temperature the planet would be if there were no atmosphere.

“A big part of the scientific value of this planet is understanding what kind of atmosphere it might have. Because Gliese 12 b lies between the amount of light that Earth and Venus receive from the Sun, it will be valuable in bridging the gap between the two. two planets in our solar system.”

Palethorpe added: ‘It is thought that the first atmospheres of Earth and Venus were stripped away and then replenished by volcanic outgassing and bombardment of residual material in the solar system.

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

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

“We have found the closest, continuous, temperate world the size of Earth yet,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, who led a research team with Akihiko Fukui, a project assistant. professor at the University of Tokyo.

“Although we don’t yet know if it has an atmosphere, we have seen it as 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 the star. Red dwarfs tend to be magnetically active, resulting in frequent, powerful X-ray flares.

However, analyzes from both teams conclude that Gliese 12 shows no signs of such extreme behavior, raising hopes that Gliese 12 b’s atmosphere is still intact.

“We know of only a handful of temperate planets that are similar to Earth and both of which are close enough to us and meet other criteria needed for this type of research, called transmission spectroscopy, using current facilities,” says Michael McElwain, a research astrophysicist at NASA’s Goddard. Space Flight Center in Greenbelt, Maryland, and co-author of the paper Kuzuhara and Fukui.

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

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

It consists of seven planets, all about the same size as Earth and probably rocky, orbiting a red dwarf star.

Three of these are in the habitable zone, but at least two (and probably all) have no atmosphere and are probably barren. When they were first discovered eight years ago, hopes that they could be water worlds capable of supporting life were dismissed.