Gliese 12 b orbits a cool red dwarf star just 40 light-years away. It promises to tell astronomers more about how planets near their stars retain or lose their atmospheres. In this artist’s impression, Gliese 12 b retains a thin atmosphere. Image credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)
Scientists have discovered Gliese 12 b, an exoplanet similar size to Venus and only 40 light years away. Studies are currently being conducted 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, named Gliese 12 b, orbits its parent star every 12.8 days, is comparable in size to Venus—slightly smaller than Earth—and has an estimated surface temperature of 42 °C (107 °F), lower than most of the roughly 5,000 exoplanets confirmed to date.
However, this assumes there is no atmosphere, which is the crucial next step in determining whether it is habitable.
The atmospheric secret of Gliese 12 b
The atmosphere of Gliese 12 b may be similar to that of Earth. It may be similar to Venus, which experienced an uncontrolled greenhouse effect that turned it into a 400 °C (752 °F) hellhole. It could also have no atmosphere, or perhaps a different type of atmosphere not found in our solar system.
Getting an answer to this is crucial, as it would shed light on whether Gliese 12 b can maintain temperatures suitable for the existence of liquid water – and possibly life – on its surface. At the same time, it would provide answers to the question of how and why Earth and Venus evolved so differently.
Gliese 12 b is by no means the first Earth-like exoplanet to be discovered, but as NASA said there are only a handful of such worlds that deserve 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 interpretations of Gliese 12 b, from one with no atmosphere to one with a thick Venus-like atmosphere. Image credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)
Gliese 12 b: A primary target for the James Webb Space Telescope
It has been described as “the closest transient temperate Earth-sized planet yet” and a potential target for further study by the US space agency’s $10 billion project. James Webb Space Telescope.
The closest Earth-like exoplanet to us – and possibly the most famous – is Proxima Centauri b, which is only 4 light-years away. However, because it is not a transiting planet, we still have a lot to learn about it, including whether it has an atmosphere and whether it can support life.
Most exoplanets are discovered using the transit method, in which a planet passes in front of its star from our perspective, causing the host star to decrease in brightness.
During a transit, the star’s light 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 the Webb telescope.
The importance of Gliese 12 b for the study of exoplanets
Gliese 12 b could also be important because it could provide information about whether the majority of stars in our Milky Way Galaxies – cool stars – are capable of hosting temperate planets with atmospheres that are therefore habitable.
The discovery of Exo-Venus by two international teams of astronomers was announced today (May 23) in the Monthly Notices of the Royal Astronomical Society.
It orbits a cool red dwarf star called Gliese 12, located nearly 40 light-years from Earth in the constellation Pisces.
Findings from researchers
“Gliese 12 b represents one of the best targets to study whether Earth-sized planets orbiting cool stars can retain their atmospheres, a crucial step in improving our understanding of the habitability of planets in our galaxy,” said Shishir Dholakia , a graduate student at the Galaxy Center for Astrophysics at the University of Southern Queensland in Australia.
He led a research team with Larissa Palethorpe, a PhD student at the University of Edinburgh and University College London.
The exoplanet’s parent star is about 27 percent the size of our Sun and its surface temperature is 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 does from the Sun and about 85 percent of the energy that Venus experiences.
Understanding atmospheric influences
This difference in solar radiation is important because it means that the planet’s surface temperature depends strongly 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 store heat and, depending on the type, can significantly change the actual surface temperature,” Dholakia explained. “We cite the planet’s ‘equilibrium temperature’, which is the temperature the planet would have if it had no atmosphere.
“Much 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 eroded and then replenished by volcanic outgassing and bombardment by residual material in the solar system.
“Earth is habitable, but Venus is not due to its complete loss of water. Because Gliese 12 b lies between Earth and Venus in temperature, its atmosphere could teach us a lot about the habitability paths 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 with their discovery.
“We have found the closest transiting temperate Earth-sized planet that has been located so far,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo who led a research team along with Akihiko Fukui, a project assistant professor at the University of Tokyo.
“Although we don’t yet know whether it has an atmosphere, we have imagined 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 storms of its star. Red dwarfs tend to be magnetically active, which leads to frequent, powerful X-ray flares.
However, both teams’ analyzes conclude 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 handful of Earth-like planets with temperate climates that are close enough to us and meet other criteria needed to do this type of study, called transmission spectroscopy, with 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 evolutionary outcomes of these planets, we need more examples like Gliese 12 b.”
Gliese 12 b is 40 light-years from Earth, about the same distance as the TRAPPIST-1 system.
This consists of seven planets, all roughly 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 of them – have no atmosphere and are probably barren, which dashed hopes that they could be watery worlds capable of supporting life when they were first discovered eight years ago.
Reference: “Gliese 12 b, a temperate Earth-sized planet 12 parsecs away, 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