Gliese 12 b, an intriguing Earth- or Venus-sized world

Earth, and three more similar planets of slightly differing sizes.
Meet Gliese 12 b. It’s a world, orbiting a distant sun. It’s portrayed in this artist’s concept as 3 possible worlds, because we don’t exactly know its size. But its size is comparable to that of Earth or Venus. Image via @NASAAstrobio on X.
  • Gliese 12 b is a newly discovered rocky exoplanet, between Earth and Venus in size. It orbits a red dwarf star 40 light-years away.
  • It may be the closest, temperate, transiting, Earth-sized exoplanet found so far. But we don’t know yet, because the computer modeling suggests various possibilities, based on subtle size differences.
  • These subtle differences make it fascinating to scientists. And they make Gliese 12 b an ideal target for further study with NASA’s Webb space telescope.

Meet exoplanet Gliese 12 b

Astronomers said on May 23, 2024, that NASA’s TESS space telescope was used to discover an intriguing rocky exoplanet between Earth and Venus in size. The planet is called Gliese 12 b. It orbits a red dwarf star, located in our sky in the direction of the constellation Pisces the Fish. Its distance is only 40 light-years. It may be the nearest, transiting, temperate, Earth-size world located to date.

“Transiting” means this world passes in front of its star from our earthly perspective. That fact makes it possible to observe with TESS, whose full name is the Transiting Exoplanet Survey Satellite.

The researchers refer to Gliese 12 b as an exo-Venus. That’s because it’s similar in size to Venus (Earth and Venus are so alike in size that they’re often called “twins). And it receives a similar amount of energy as Venus from its star. But astronomers don’t yet know if Gliese 12 b has an atmosphere, or what kind it may have. One of the researchers, Masayuki Kuzuhara, said in a statement:

Although we don’t yet know whether it possesses an atmosphere, we’ve been thinking of it as an exo-Venus, with similar size and energy received from its star as our planetary neighbor in the solar system.

The uncertainties about Gliese 12 b center on its possible atmopshere. If it doesn’t have an atmosphere, computer models indicate its average surface temperature are slightly warmer than Earthlike, with an average temperature of only around 107 degrees Fahrenheit (42 degrees Celsius). That’s in contrast to Venus, whose average surface temperature is around 870°F (465°C). The researchers said there are various possibilities regarding its atmosphere and subsequent temperature, though. The possibilities range from no atmosphere for Glise 12 b to a thick Venus-like atmosphere.

Astronomers want to know the details of this exoplanet. That’s because worlds like this one might be habitable, perhaps not by earthlings, but possibly by some form of life. And being only 40 light-years away makes it well-suited for follow-up observations with NASA’s James Webb Space Telescope.

A lot of energy from a small, cool star

The planet’s star is a red dwarf, smaller and cooler than our own sun. The red dwarf is only 27% the size of our sun and emits only 60% as much heat. So why does Gliese 12 b receive almost as much energy from its star – about 85% – as Venus? It’s because it orbits much closer to its star. In fact, it completes an orbit in only 12.8 days. So even though the star is cooler, the planet still receives as much heat from its star as Venus does from our sun.

The distance of Gliese 12 b to its star is just 7% of the distance from Earth to the sun. Being so close means, it receives 1.6 times as much energy from its star as Earth does from our sun.

It’s also easier for astronomers to detect rocky Earth-sized planets around red dwarf stars than larger stars like our sun. That’s due to their lower luminosity. Gliese 12 b is one of the best examples of this found so far. As Dholakia said:

Gliese 12 b represents one of the best targets to study whether Earth-size planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on planets across our galaxy.

Who made the discovery?

The first team was led by Shishir Dholakia at the Centre for Astrophysics at the University of Southern Queensland in Australia and Larissa Palethorpe at the University of Edinburgh and University College London. This team published its peer-reviewed findings in the Monthly Notices of the Royal Astronomical Society on May 23, 2024.

Masayuki Kuzuhara and Akihiko Fukui at the University of Tokyo in Japan co-led the second team. They published their own peer-reviewed paper on the same day, in The Astrophysical Journal Letters.

Besides TESS, the astronomers also used the MuSCAT2 camera at the Observatories of the Canary Islands (OCAN), and well as the MuSCAT3 camera at Haleakala High Altitude Observatory, the Subaru Telescope, Gemini Observatory and W. M. Keck Observatory in Hawaii.

Earth-like temperatures or Venus twin?

The researchers don’t yet know what kind of atmosphere Gliese 12 b has, or if it even has one at all. In many cases, a rocky planet so close to a red dwarf star means intense radiation from the star can strip away any atmosphere. Analysis by both teams, however, showed this particular red dwarf isn’t as extreme in its behavior. That could mean Gliese 12 b still has an atmosphere, but only further studies will be able to determine that or not.

The astronomers calculated the planet has an equilibrium temperature of 107 degrees Fahrenheit (42 degrees Celsius). (Equilibrium temperature is when thermal energy radiated balances solar energy absorbed, so the temperature does not change.) So, 107 degrees Fahrenheit is only a bit warmer than Earth on average. But it’s also if the planet has no atmosphere. If it does have an atmosphere, then the type of gases in it, density and so forth will have an impact on temperature. The planet might still be similar to Earth, or it could be a blazing-hot world more like Venus.

Implications for other rocky exoplanets

Finding out what the actual conditions are will help astronomers learn more about other potentially habitable exoplanets as well. Palethorpe explained:

It is thought that Earth’s and Venus’ first atmospheres were stripped away and then replenished by volcanic outgassing and bombardments from residual material in the solar system. The 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 could teach us a lot about the habitability pathways planets take as they develop.

Co-author Michael McElwain, a research astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, added:

We know of only a handful of temperate planets similar to Earth that are both close enough to us and meet other criteria needed for this kind of study, called transmission spectroscopy, using current facilities. To better understand the diversity of atmospheres and evolutionary outcomes for these planets, we need more examples like Gliese 12 b.

Gliese 12 b: Brownish planet with no clouds and bright pinkish star nearby.
View larger. | Artist’s concept of Gliese 12 b, a Venus-sized exoplanet about 40 light-years away. It may have temperate Earth-like temperatures or hot, searing temperatures like Venus. It all depends on what kind of atmosphere it has … if it does have one. Image via NASA/ JPL-Caltech/ R. Hurt (Caltech-IPAC).

Bottom line: Two teams of astronomers have discovered a Venus-sized exoplanet 40 light-years away. It may have Earth-like temperatures or be more like a hot Venus.

Source: Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TESS and CHEOPS

Source: Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Transmission Spectroscopy


Read more: Earth-sized exoplanet discovered around ultracool dwarf star

Read more: Possible atmosphere on rocky exoplanet found for 1st time

May 29, 2024

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