TESS finds new planet perfect for studying atmospheres

Gliese 12 b's estimated size may be as large as Earth or slightly smaller—comparable to Venus in our solar system. This artist's concept compares Earth with different possible Gliese 12 b interpretations, from one with no atmosphere to one with a thick Venus-like one. Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC).

Astronomers using NASA’s TESS (Transiting Exoplanet Survey Satellite) and other observatories have discovered an intriguing planet between the sizes of Earth and Venus, located just 40 light-years away.

This planet, named Gliese 12 b, offers exciting opportunities for further study with NASA’s James Webb Space Telescope.

TESS observes large sections of the sky for about a month at a time, monitoring tens of thousands of stars for changes in brightness.

These changes, called transits, occur when a planet passes in front of its star, causing a brief dimming. One of TESS’s main goals is to find these transiting planets.

Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo, co-led one of the research teams with Akihiko Fukui, a project assistant professor at the University of Tokyo.

Kuzuhara explained, “We’ve found the closest Earth-size world that transits its star and is in a temperate zone. Although we don’t know if it has an atmosphere, we think of it as an exo-Venus, with similar size and energy from its star as Venus receives.”

Gliese 12, the star hosting this planet, is a cool red dwarf located in the constellation Pisces. This star is about 27% the size of our sun and has 60% of its surface temperature.

Gliese 12 b orbits its star every 12.8 days and is about the size of Earth or slightly smaller, comparable to Venus. If it lacks an atmosphere, its surface temperature would be around 107 degrees Fahrenheit (42 degrees Celsius).

Red dwarf stars like Gliese 12 are excellent for finding Earth-size planets because their smaller size makes the dimming during a transit more noticeable. Additionally, their lower mass means that orbiting planets can create a greater “wobble” in the star, making detection easier.

Red dwarfs also have habitable zones, areas where liquid water could exist on a planet’s surface, that are closer to the star. This proximity makes it easier to detect transiting planets within these zones.

Gliese 12 b is located only 7% of the distance between Earth and the sun from its star. It receives 1.6 times more energy from its star than Earth does from the sun, and about 85% of what Venus experiences.

“Gliese 12 b is an excellent target to study whether Earth-size planets orbiting cool stars can retain their atmospheres,” said Shishir Dholakia, a doctoral student at the Centre for Astrophysics at the University of Southern Queensland in Australia. Dholakia co-led another research team with Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London.

Studying Gliese 12 b could provide insights into our own solar system’s evolution. Palethorpe explained, “Earth and Venus had their first atmospheres stripped away and then replenished by volcanic activity and impacts from space debris.

The Earth is habitable, but Venus lost its water. Gliese 12 b, with a temperature between Earth and Venus, could teach us about the pathways planets take as they develop.”

A key factor in retaining an atmosphere is the activity of the star. Red dwarfs can be magnetically active, causing frequent, powerful X-ray flares. However, both research teams found that Gliese 12 shows no signs of extreme behavior.

The findings by Kuzuhara and Fukui were published in The Astrophysical Journal Letters, while the Dholakia and Palethorpe findings appeared in Monthly Notices of the Royal Astronomical Society.

During a transit, the star’s light passes through any atmosphere the planet may have. Different gases absorb different colors of light, providing a set of chemical fingerprints detectable by telescopes like Webb.

Michael McElwain, a research astrophysicist at NASA’s Goddard Space Flight Center and co-author of the Kuzuhara and Fukui paper, said, “We know of only a few temperate planets similar to Earth that are close enough and meet the criteria for this kind of study using current facilities. To understand the diversity of atmospheres and outcomes for these planets, we need more examples like Gliese 12 b.”

TESS is managed by NASA Goddard and operated by MIT, with many partners including Northrop Grumman, NASA’s Ames Research Center, and the Center for Astrophysics | Harvard & Smithsonian. Numerous universities, research institutes, and observatories worldwide are involved in the mission.