Discovered2009MEarth Project, Charbonneau et al.[2]
About the image. Drawn as a featureless planet wrapped in pale, reflective haze, as JWST measurements suggest. What lies beneath the haze is unknown.
14×as wide as our Sun looks from Earth
17×the light Earth gets
No ground: the view from the cloud tops
The sky from GJ 1214 b
GJ 1214 would look 14× as wide as the Sun does from Earth, and the planet gets 17× as much light as Earth gets.
Its colour comes from its surface temperature of 3 101 K (2 830 °C); the Sun's is about 5 772 K (5 500 °C).
How fast GJ 1214 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.
In 2009 David Charbonneau’s MEarth project, a set of small robotic telescopes watching nearby red dwarfs, caught a dip of about 1.5 percent in the light of the star GJ 1214, repeating every 38 hours. The planet causing it was between Earth and Neptune in size and mass, a kind of planet our Solar System does not have. Its density fitted a world made largely of water, and it quickly became famous as the best candidate for a “water world”.
Hidden under haze
To find out, astronomers tried to read its atmosphere as it crossed the star. They got almost nothing. In 2010 its spectrum turned out flat and featureless: no thick, clear hydrogen atmosphere, but something hiding whatever lies below, either steam or high clouds. For years every new attempt hit the same wall of haze.
Fifteen transits with Hubble
The most thorough attempt before JWST showed that the planet must have clouds, and high ones. Kreidberg and colleagues watched 15 transits with Hubble’s Wide Field Camera 3 between September 2012 and August 2013, and the spectrum was still flat. That ruled out, at more than 5σ confidence, cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen or carbon dioxide. The team named zinc sulfide and potassium chloride as possible cloud materials, although these form much deeper and would have to be lifted far up; a photochemical haze of hydrocarbons was the alternative.
What JWST found
In 2023 Eliza Kempton and colleagues used the James Webb Space Telescope to follow the planet around its whole orbit, measuring its day and night sides. The day side is about 553 K (280 °C) and the night side about 437 K (164 °C), and the planet reflects about half of the light that hits it, which makes it unusually bright. They concluded it has a reflective atmosphere rich in heavier elements. Later studies found possible carbon dioxide above the haze and suggested it may resemble a scaled-up Venus more than an ocean.
Models informed by those measurements now call a true water world implausible; a thick envelope of hydrogen, helium, water and other volatiles is more likely. The planet is also losing about 900 tonnes of atmosphere every second, so the atmosphere it has now is probably not the one it was born with.
Its orbit, to scale
GJ 1214 b goes around once every 1.6 days, at 0.01505 AU from its star. The whole view is tiny on Solar System scale: Mercury orbits the Sun about 26 times farther out than the outermost orbit shown here.
GJ 1214 b: equilibrium temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
GJ 1214 b is about 48 light-years away.
Light299 792 km/s48 years
Breakthrough Starshotplanned light sail, 20% of light speed240 years
Parker Solar Probefastest spacecraft so far, 192 km/s74 948 years
Voyager 1leaving the Solar System, 17 km/s846 472 years
At Voyager 1's speed the trip would take about 10 581 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Your weight on GJ 1214 b
On GJ 1214 b
Gravity there is about 1.13× Earth's, at the top of its haze; it may have no solid surface. Calculated from the measured mass and radius.
Gallery
A pale cream crescent of a planet beside a small, dim red star on the left, an impression of GJ 1214 b. AI-generated painting.The smooth, hazy salmon-pink face of a planet filling most of the frame, an impression of GJ 1214 b. AI-generated painting.GJ 1214 b, 3D artist's impression, rendered from the interactive model.GJ 1214 b, 3D artist's impression, from another angle, rendered from the interactive model.GJ 1214 b, 3D artist's impression, close-up, rendered from the interactive model.
Timeline
2009Discovered by the MEarth Project and hailed as a possible water world.
2010Its spectrum turns out flat: haze or clouds hide the atmosphere.
2023JWST finds a bright, reflective, metal-rich atmosphere.
2024Models call a true water world implausible.
Questions people ask
Is GJ 1214 b a water world?
Probably not in the classic sense. JWST results and later models favour a thick, hazy, metal-rich atmosphere.
What is a mini-Neptune?
A planet between Earth and Neptune in size, with a thick atmosphere. Our Solar System has none.