Gliese 12 b: An Intriguing World Sized Between Earth and Venus

Released Thursday, May 23, 2024

ID: 14581

- Art:
- Robert Hurt
- Written by:
- Francis Reddy
- Produced by:
- Scott Wiessinger
- Scientific consulting by:
- Michael W. McElwain

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 no atmosphere to a thick Venus-like one. Follow-up observations with NASA’s James Webb Space Telescope will help determine just how much atmosphere the planet retains as well as its composition.

Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

Alt text: Illustration of Earth compared to various models of Gliese 12 b

Image description: At left, against a black background, floats an artist's concept of a nearly half-illuminated Earth, with clouds, blue oceans, and land areas rendered in green, tan, brown, and white. At right are three similarly illuminated planets, slightly smaller than Earth and each representing a possible interpretation of Gliese 12 b. The version on the left has a surface of blotchy reddish and brownish features and no atmosphere. The middle version has the same surface texture partly obscured by a hazy atmosphere. And the rightmost and smallest version of the planet has a thick, Venus-like atmosphere that obscures the surface completely.

Using observations by NASA’s TESS (Transiting Exoplanet Survey Satellite) and many other facilities, two international teams of astronomers have discovered an exciting planet between the sizes of Earth and Venus only 40 light-years away. It is the nearest, transiting, temperate, Earth-size world located to date.

Astronomers say it's a unique candidate for further atmospheric study. Earth remains habitable, but Venus does not due to its complete loss of water. If Gliese 12 b retains some atmosphere, it could teach us a lot about the habitability pathways planets take as they develop.

TESS stares at a large swath of the sky for about a month at a time, tracking the brightness changes of tens of thousands of stars at intervals ranging from 20 seconds to 30 minutes. Capturing transits — brief, regular dimmings of stars caused by the passage of orbiting worlds — is one of the mission’s primary goals.

The host star, called Gliese 12, is a cool red dwarf located almost 40 light-years away in the constellation Pisces. The star is only about 27% of the Sun’s size, with about 60% of the Sun’s surface temperature. The new world, named Gliese 12 b, orbits every 12.8 days and is Earth’s size or slightly smaller — comparable to Venus. Assuming it has no atmosphere, the planet has a surface temperature estimated at around 107 degrees Fahrenheit (42 degrees Celsius).

The distance separating Gliese 12 and the new planet is just 7% of the distance between Earth and the Sun. The planet receives 1.6 times more energy from its star as Earth does from the Sun and about 85% of what Venus experiences.

One important factor in retaining an atmosphere is the storminess of its star. Red dwarfs tend to be magnetically active, resulting in frequent, powerful X-ray flares. However, analyses by both teams conclude that Gliese 12 shows no signs of extreme behavior.

During a transit, the host star’s light passes through any atmosphere, effectively sampling it. Different gas molecules absorb different colors, so the transit provides a set of chemical fingerprints that can be detected by facilities like NASA's James Webb Space Telescope.

Gliese 12 b, which orbits a cool red dwarf star located 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 retaining a thin atmosphere.

Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

Alt text: Space scene of a thin atmosphere version of Gliese 12 b

Image description: Against a starry background, a bright, reddish star shines at lower left. At right, the body of a planet dominates the view, its hazy limb arcing from top center to bottom right. The planet's body is mottled in red and brown hues, the details softened by a slight atmospheric haze.

Gliese 12 b, which orbits a cool, red dwarf star located 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 thick atmosphere similar to that of Venus in our solar system.

Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

Alt text: Space scene of a Venus-like version of Gliese 12 b

Image description: Against a starry background, a bright, reddish star shines at lower left. At right, the body of a planet dominates the view, its hazy limb arcing from top center to bottom right. A thick, yellow-brown atmosphere obscures any view of its surface.

In this sequence, the camera starts close to a Venus-like artist's concept of Gliese 12 b set against a starry background. As the camera pulls back and spins, the planet shrinks, the stars whirl, and the planet's host star eventually appears. The planet passes across the star's face, creating a transit. Passing through the planet's atmosphere, the host star's light is partly absorbed, encoding into it the chemical fingerprints of the atmosphere's component elements. Gliese 12 b is one of the best candidates for this type of study.

Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)