TESS Discovers Earth-Sized World in Habitable Zone of Nearby Star

Two international teams of astronomers using data from NASA’s Transiting Exoplanet Survey Satellite (TESS)  and other facilities have discovered a fascinating world between the sizes of Earth and Venus, a mere 40 light-years away. This newly discovered planet, named Gliese 12 b, holds promise for revealing secrets about how planets close to their stars retain or lose their atmospheres, and potentially about the evolution of our own solar system.

Gliese 12 b orbits a cool red dwarf star called Gliese 12, located in the constellation Pisces. Red dwarf stars are smaller and cooler than our Sun, and the habitable zone – the range of distances where liquid water could exist on a planet’s surface – is much closer to them. This proximity makes it easier to detect transiting planets within the habitable zone of red dwarf stars compared to stars like our Sun.

Gliese 12 b orbits its star every 12.8 days and is estimated to be either similar in size to Earth or slightly smaller, making it the nearest transiting, temperate, Earth-size world located to date. While the planet receives about 1.6 times more energy from its star than Earth does from the Sun, it still resides within the habitable zone of Gliese 12 due to the star’s cooler temperature.

“We’ve found the nearest, transiting, temperate, Earth-size world located to date,” said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, who co-led a research team with Akihiko Fukui. “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,” Kuzuhara added.

One key factor in determining whether a planet can retain an atmosphere is the activity level of its host star. Red dwarf stars are known for being magnetically active, which can result in frequent and powerful X-ray flares that could strip away a planet’s atmosphere. However, analyses by both teams suggest that Gliese 12 shows no signs of extreme stellar behavior, offering hope that Gliese 12 b might have retained an atmosphere .

Studying the atmosphere of Gliese 12 b will be crucial for understanding its potential habitability. During a transit, some of the host star’s light passes through the planet’s atmosphere, and different gas molecules absorb different colors of light. By analyzing this light using telescopes like the James Webb Space Telescope, scientists can potentially identify the chemical fingerprints of gases present in the atmosphere.

“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,” said Michael McElwain, a research astrophysicist at NASA’s Goddard Space Flight Center and co-author of a paper led by Kuzuhara and Fukui. “To better understand the diversity of atmospheres and evolutionary outcomes for these planets, we need more examples like Gliese 12 b,” McElwain emphasized.

The findings from these studies were published on May 23, 2024, in two separate papers: one led by Kuzuhara and Fukui in The Astrophysical Journal Letters, and the other by Shishir Dholakia (Centre for Astrophysics, University of Southern Queensland) and Larissa Palethorpe (University of Edinburgh and University College London) in Monthly Notices of the Royal Astronomical Society.

This discovery by TESS adds to the growing list of intriguing exoplanets potentially harboring conditions suitable for life. Further observations using powerful telescopes like James Webb could shed light on the atmospheric composition of Gliese 12 b and bring us closer to understanding the possibility of life on this nearby world.