Discovered2024TESS, announced by two teams on 23 May[3]
About the image. Drawn as a rocky world about Earth's size beside a small red star. Gliese 12 b has never been seen; it is known from the slight dimming of its star as it passes in front, and whether it has an atmosphere is unknown, so its surface here is imagined.
4.0×as wide as our Sun looks from Earth
1.7×the light Earth gets
The sky from Gliese 12 b
Gliese 12 would look 4.0× as wide as the Sun does from Earth, and the planet gets 1.7× as much light as Earth gets.
Its colour comes from its surface temperature of 3 328 K (3 050 °C); the Sun's is about 5 772 K (5 500 °C).
How fast Gliese 12 b spins is unknown, so the length of its day is too.
Apparent size = star radius ÷ orbit; light = size² × (temperature ÷ 5 772 K)⁴. Both from the values on this page. The landscape is imagined.
On 23 May 2024 two teams of astronomers announced the same discovery: a planet about the size of Earth, crossing the face of a small red star only 40 light-years away. Both had found it in data from NASA’s TESS satellite, which watches for the slight dips in starlight that passing planets cause; one team confirmed it with Europe’s CHEOPS telescope. The planet is called Gliese 12 b, after its star.
Between Earth and Venus
Gliese 12 b is about Earth’s width or a little smaller, close to the size of Venus. It goes round its star every 12.76 days at 0.067 AU, much closer in than Mercury is to the Sun. But Gliese 12 is a red dwarf with about a quarter of the Sun’s mass and a surface of about 3 330 K (3 060 °C), so the planet receives only about 1.6 times as much energy as Earth gets from the Sun, about 85% of what Venus gets.
That puts it between the two worlds. If it has no atmosphere and reflects no light, its surface would be around 315 K (42 °C). Whether it is a temperate world, a hot exo-Venus under a thick blanket of carbon dioxide or a bare rock depends entirely on an atmosphere nobody has yet detected.
How heavy is it?
The discovery papers could only set upper limits on its mass. In 2025 two teams measured it from the tiny wobble the planet causes in its star, and came out with different answers: about 0.95 Earth masses in one study and about 0.70 in the other. The first gives a density of about 6.4 grams per cubic centimetre, close to Earth’s; the second would make it noticeably less dense than Earth. Both agree it is roughly Earth-like in size and mass.
Does it have air?
Gliese 12 b is one of the best places to look for an atmosphere around an Earth-sized planet. Its star is close and quiet, and the discovery team found it about as well suited to study with the James Webb Space Telescope as the planets of TRAPPIST-1. The signal will be small: any atmosphere would change the starlight passing through it by less than about a hundredth of a percent. A study published in 2025 calculated that any hydrogen the planet started with would have been stripped away within its first 150 million years, so whatever air it has now would have to be heavier gas, as on Earth or Venus.
So far no atmosphere has been detected. It was considered for Webb’s Rocky Worlds programme in 2025 but was not among the nine final targets, and a Hubble programme is searching for hydrogen escaping from it.
Its orbit, to scale
Gliese 12 b goes around once every 13 days, at 0.067 AU from its star. The whole view is tiny on Solar System scale: Mercury orbits the Sun about 6 times farther out than the outermost orbit shown here.
Earth days passing: 0
How hot is it?
Earth (average)288 K · 15 °C
Water boils373 K · 100 °C
Venus surface737 K · 464 °C
Iron melts1 811 K · 1 540 °C
Sun's surface5 772 K · 5 500 °C
Gliese 12 b315 K · 42 °C
Gliese 12 b: equilibrium temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
Gliese 12 b is about 39.8 light-years away.
Light299 792 km/s40 years
Breakthrough Starshotplanned light sail, 20% of light speed199 years
Parker Solar Probefastest spacecraft so far, 192 km/s62 144 years
Voyager 1leaving the Solar System, 17 km/s701 866 years
At Voyager 1's speed the trip would take about 8 773 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Gallery
A dull red star on the left and a tan, rocky planet lit from that side through a thin haze, an impression of Gliese 12 b beside its small red star. AI-generated painting.A large, dim red sun low over a dry, rocky desert under a hazy orange-pink sky, an impression of the view from the surface of Gliese 12 b. AI-generated painting.Gliese 12 b, 3D artist's impression, rendered from the interactive model.Gliese 12 b, 3D artist's impression, from another angle, rendered from the interactive model.Gliese 12 b, 3D artist's impression, close-up, rendered from the interactive model.
Timeline
2024Two teams announce Gliese 12 b on 23 May, found by TESS.
2025Two teams measure its mass and disagree: about 0.95 and 0.70 Earth masses.
2025It is considered for Webb's Rocky Worlds programme but not chosen as a final target.
Questions people ask
How far away is Gliese 12 b?
About 40 light-years, which makes it one of the nearest Earth-sized planets known to cross the face of its star.
Is Gliese 12 b habitable?
Nobody knows. It receives 1.6 times as much energy as Earth, between Earth and Venus, and whether it has an atmosphere is not yet known.
Does Gliese 12 b have an atmosphere?
Not yet known. It is one of the best targets for finding out, because its star is close and quiet.