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 shown with a thin atmosphere preserved. Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)
Scientists have discovered Gliese 12 b, an exoplanet similar in size to Venus and only 40 light-years away, with ongoing research to determine its atmosphere and potential to support life.
In a rare and tantalizing discovery, astronomers have discovered an Earth-like exoplanet 40 light-years away that may be slightly warmer than our own world.
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.
The Atmospheric Mystery of Gliese 12 b
Gliese 12 b’s atmosphere may resemble Earth’s. It may reflect Venus experiencing a greenhouse effect that turned it into a 400°C (752°F) hellhole. There may also be no atmosphere, or perhaps a different kind of atmosphere 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 differently .
Gliese 12 b is by no means the first Earth-like exoplanet discovered, but as NASA said that there are only a few worlds like it that deserve a closer look.
The approximate size of Gliese 12 b could be the size of Earth or slightly smaller – comparable to Venus in our solar system. This artist’s concept compares Earth to various possible interpretations of Gliese 12 b, from one without an atmosphere to one with a dense, Venus-like one. Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)
Gliese 12 b: Primary target for the James Webb Space Telescope
It has been declared the “closest, transiting, temperate Earth-sized world found to date” and a potential target for the US space agency’s $10 billion further investigation James Webb Space Telescope.
The closest Earth-like exoplanet to us – and probably the most famous – is Proxima Centauri b, which is only 4 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.
The importance of Gliese 12 b in exoplanet research
Gliese 12 b could also be significant because it could help reveal whether most of the stars in ours Milky Way galaxy – i.e. cool stars – are capable of hosting temperate planets that have atmospheres and are therefore habitable.
The discovery of an ‘exo-Venus’ by two international teams of astronomers was published today (May 23) in Monthly Notices of the Royal Astronomical Society.
It orbits a cold red dwarf star called Gliese 12, which is nearly 40 light-years from Earth in the constellation Pisces.
Insights from researchers
“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 percent the size of our Sun and has a surface temperature that is about 60 percent that of our own star.
However, the distance separating Gliese 12 and the new planet is only 7 percent of the distance between Earth and the Sun. Therefore, Gliese 12 b receives 1.6 times as much energy from its star as Earth does from the Sun, and about 85 percent of what Venus experiences.
Understanding weathering
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. Since Gliese 12 b falls 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.
Pailthorpe added: “The first atmospheres of Earth and Venus are thought to have been removed and then rebuilt by volcanic gases and bombardment of remnant material in the Solar System.
“Earth is habitable, but Venus is not because of 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, moderate Earth-sized world found so far,” said Masayuki Kuzuhara, a project assistant professor at the Tokyo Astrobiology Center who led a research team with Akihiko Fukui, a project assistant professor at the Tokyo university.
“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 both 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 NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and Kuzuhara and Fukui co-authored the paper.
“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.
Reference: “Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TPP and CHEOPS” Shishir Dholakia and Larissa Palethorpe et al. May 23, 204 Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stae1152
