Gliese 12 b, which orbits a cool, red dwarf star just 40 light-years away, promises to tell astronomers more about how planets close to their stars retain or lose their atmospheres. In this artist’s concept, Gliese 12 b is depicted while maintaining a rarefied atmosphere. Credit: NASA/JPL-Caltech/R. Pain (Caltech-IPAC)
Scientists have discovered Gliese 12 b, a exoplanet similar in size to Venus and only 40 light-years away, with studies underway to determine its atmosphere and potential to support life.
In a rare and tantalizing discovery, astronomers have found an Earth-like exoplanet 40 light-years away that may be just a little warmer than our own world.
The potentially habitable planet, called Gliese 12 b, orbits its host 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). lower 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.
The atmospheric mystery of Gliese 12 b
Gliese 12 b’s atmosphere could resemble Earth’s. It could be a reflection of Venus, which experienced a runaway greenhouse effect that turned it into a 400 °C (752 °F) hellhole. It could also have no atmosphere, or perhaps some other type of atmosphere not found in our solar 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 it is NASA has said: there are only a handful of such worlds that warrant a closer look.
The estimated size of Gliese 12 b could be as large as Earth, or slightly smaller – comparable to Venus in our solar system. This artist’s concept compares Earth to several possible Gliese 12 b interpretations, from one with no atmosphere to one with a thick Venus-like one. Credit: NASA/JPL-Caltech/R. Pain (Caltech-IPAC)
Gliese 12 b: a prime target for the James Webb Space Telescope
It has been billed as “the closest, continuous, temperate Earth-sized world yet found” and a potential target for further exploration by the $10 billion US space agency. 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.
The significance of Gliese 12 b in the study of exoplanets
Gliese 12 b could also be significant, as it could help reveal whether the majority of stars in our Milky Way Galaxies – that is, cool stars – are capable of hosting temperate planets that have an atmosphere and are therefore habitable.
The discovery of the ‘exo-Venus’, by two international teams of astronomers, was published today (May 23) in the Monthly notices of the Royal Astronomical Society.
It orbits a cool red dwarf star called Gliese 12, which is nearly 40 light-years away from Earth in the constellation Pisces.
Insights from researchers
“Gliese 12 b is one of the best targets to investigate whether Earth-sized planets orbiting cool stars can maintain their atmospheres, a crucial step in increasing 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 percent the size of our Sun and has a surface temperature about 60 percent that of our own star.
However, the distance between Gliese 12 and the new planet is only 7 percent 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 percent of what Venus experiences.
Insight into atmospheric influences
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 their 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 it had 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 these 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 because of the complete loss of water. Because Gliese 12 b is temperature-wise between Earth and Venus, Gliese’s atmosphere can teach us a lot about the habitability pathways that planets take as they evolve.”
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 transiting 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, 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 likely sterile, dashing hopes when they were first discovered eight years ago that they could be water worlds harboring life .
Reference: “Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TESS and CHEOPS” Shishir Dholakia and Larissa Palethorpe et al. May 23, 204, Monthly notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stae1152