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Astronomers have made the rare and tantalizing discovery of an Earth-like exoplanet 40 light-years away that may be slightly warmer than our world. The new paper, “Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TESS and CHEOPS,” is published in Monthly Notices of the Royal Astronomical Society.

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

However, this implies that there is no atmosphere, which is the crucial next step in determining whether it is habitable. It could have an Earth-like atmosphere closer to that of Venus – which experienced a greenhouse effect that turned it into a 400°C (752°F) hellhole – no atmosphere, or perhaps a different kind of atmosphere. which is not found in our solar system.

Getting an answer is vital because it will reveal whether Gliese 12 b can support temperatures suitable for liquid water – and possibly life – to exist on its surface, while unlocking answers about how and why Earth and Venus evolved so different.

Gliese 12 b is by no means the first Earth-like exoplanet discovered, but as NASA said, there are only a few worlds like it that deserve a closer look.

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

The closest Earth-like exoplanet to us – and probably the best known – is Proxima Centauri b, which is just four light-years away. However, since it is not a transiting 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, where a planet passes in front of its star from our point of view, causing the host star to drop in brightness.

During transit, starlight also passes through an exoplanet’s atmosphere and some 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 significant because it could help reveal whether the majority of stars in our Milky Way galaxy—i.e. cool stars – are capable of hosting temperate planets that have atmospheres and are therefore habitable.

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

“Gliese 12 b represents one of the best targets for investigating 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 PhD student at the Center for Astrophysics at the University of Southern Queensland in Australia.

He leads a research team with Larissa Pailthorpe, a PhD 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 separating Gliese 12 and the new planet is only 7% of the distance between Earth and the sun. Therefore, Gliese 12 b 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 planet’s surface temperature is highly dependent on its 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 the type – can significantly change the actual surface temperature,” Dholakia explained. “We quote the ‘equilibrium temperature’ of the planet, which is the temperature the planet would be if it had no atmosphere.

“A big part of the scientific value of this planet is figuring out 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 planets in our solar system.”

Palethorpe added: “The first atmospheres of Earth and Venus are thought to have been stripped away and then rebuilt by volcanic gases and bombardment of remnant material in the Solar System.

“Earth is habitable, but Venus is not due to its complete loss of water. Because Gliese 12 b is between Earth and Venus in temperature, its atmosphere can teach us a lot about the habitable paths planets take as they evolve.”

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

“We found the closest, transiting, temperate Earth-sized world located to date,” said Masayuki Kuzuhara, a project assistant at the Tokyo Astrobiology Center, 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 thought of 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 preserving the atmosphere is the turbulent nature of its star. Red dwarfs tend to be magnetically active, resulting in frequent, powerful X-ray bursts.

However, the two teams’ analyzes concluded that Gliese 12 shows no signs of such extreme behavior, raising hopes that Gliese 12 b’s atmosphere may still be intact.

“We know of only a few temperate Earth-like planets that are 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 Goddard of NASA Space Flight Center in Greenbelt, Maryland, and co-author of the paper Kuzuhara and Fukui.

“To better understand the diversity of atmospheres and 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.

This consists of seven planets, all roughly Earth-sized and possibly rocky, orbiting a red dwarf star.

Three of them are in the habitable zone, but at least two—and possibly all—have no atmosphere and are likely barren, dashing hopes when they were first discovered eight years ago that they might be water worlds containing life.