A sea without shores under another sun, imagined from a planet we have only seen as a blink
An ocean world
3D landscape · Kepler-22b, 640 light years away
Land here and explore →Kepler-22b was announced by NASA in December 2011 as the first planet found by the Kepler space telescope in the habitable zone of a Sun-like star, the range of distances where a planet with the right atmosphere could keep liquid water on its surface. We have never seen it directly. Everything we know comes from a tiny, regular dip in its star's light as the planet passes in front of it. In this app you can land on an ocean world inspired by Kepler-22b and explore it in interactive 3D, standing on a lone rock islet in a sea without shores.
That scene is an impression, not a photograph. It is labelled 'inferred from data' because it combines what has been measured, the planet's size, orbit and star, with one plausible guess about what such a world could be like. This guide explains what is known, what is not, and how astronomers hope to find out.
Key facts
- Radius
- ≈ 2.4 × Earth'sEstimates vary; some recent analyses suggest slightly smaller
- Mass
- Not well measuredOnly upper limits exist, so its density is uncertain
- Orbit
- ≈ 290 daysAbout 85% of Earth's distance from the Sun
- Distance
- About 600–640 light yearsIn the constellation Cygnus, near its border with Lyra
- Host star
- Kepler-22, a G-type starSlightly smaller and cooler than the Sun
- Discovery
- Announced December 2011By NASA's Kepler space telescope, using the transit method
- Habitable zone
- InsideMeans liquid water is possible, not that it exists
- Surface
- UnknownCould be a water world, or a mini-Neptune with no solid surface
- In this app
- Inferred from dataThe scene is an artist's and scientist's impression
What we know about Kepler-22b
Kepler-22b orbits its star once every 290 days or so, a little closer than Earth orbits the Sun. Because its star is slightly smaller and cooler than ours, the planet receives roughly the same amount of starlight as Earth, placing it within the star's habitable zone. If it had an Earth-like atmosphere with a modest greenhouse effect, its surface could be mild.
Its size is the key measurement. At about 2.4 times Earth's radius, Kepler-22b is larger than any rocky planet in our Solar System but much smaller than Neptune. Planets of this size are common in our galaxy, yet we have none nearby to compare with. To know what Kepler-22b is made of, astronomers need its mass as well as its size, and so far measurements of how much it tugs on its star have only been able to set upper limits.
Water world or mini-Neptune?
Studies of many exoplanets suggest that worlds much larger than about 1.6 times Earth's radius often hold thick envelopes of hydrogen and helium. Kepler-22b could therefore be a mini-Neptune with no solid surface, or a water world with a deep ocean. Both remain possible.
What is an ocean world?
Scientists use 'ocean world' for any body with a large amount of liquid water, now or in the past. In our own Solar System, Earth is the only one with oceans on its surface, but several icy moons, including Europa, Enceladus, Ganymede and Titan, are thought to have oceans hidden beneath their ice.
For exoplanets, a 'water world' usually means a planet in which water makes up a large share of its mass, perhaps tens of per cent, compared with well under one per cent for Earth. Such a planet might have a global ocean hundreds of kilometres deep with no continents at all. At the bottom, the crushing pressure would turn water into dense forms of ice, which might separate the ocean from the rocky interior below. Researchers have also proposed 'hycean' worlds, ocean-covered planets with hydrogen-rich atmospheres, as a possible class of habitable planet.
Finding planets by their blink
Kepler-22b was found by the transit method. When a planet passes directly between its star and us, it blocks a small fraction of the star's light, and the star appears to dim very slightly for a few hours before returning to normal. If the same dip repeats at regular intervals, it may be caused by an orbiting planet. Kepler-22b dims its star by only about 0.05%, a blink far too small to see with the eye.
The depth of the dip reveals the planet's size relative to its star, and the time between dips gives the length of its year. Kepler, launched in March 2009, stared at about 150,000 stars in one patch of sky in Cygnus and Lyra, measuring their brightness with extraordinary precision. Before it retired in 2018 it had found more than 2,600 confirmed planets. The method only works when an orbit happens to be lined up edge-on to us, so for every transiting planet there are many more we cannot see this way.
Reading a distant atmosphere
During a transit, a little starlight passes through the edge of the planet's atmosphere on its way to us. Different gases absorb different colours, leaving faint fingerprints in the starlight. By comparing the spectrum during and outside transit, a technique called transmission spectroscopy, telescopes can identify molecules such as water vapour, methane and carbon dioxide. A thick, hydrogen-rich atmosphere produces stronger signals than a thin one, which itself helps distinguish a mini-Neptune from a rocky or watery world.
The James Webb Space Telescope has already used this method on several small planets, including some proposed as possible water worlds, though results for such planets are often debated. Kepler-22b is distant and transits only once every 290 days, making it a hard target. Future missions such as ESA's PLATO and Ariel, and NASA's proposed Habitable Worlds Observatory, are designed to find and study more temperate planets around Sun-like stars.
The scene in this app
In the app, Kepler-22b is shown as a world of open ocean under a hazy, humid sky, with a single dark rock breaking the surface and a sun a little cooler and more golden than ours. The gravity, temperature and atmosphere you see are assumptions chosen to fit one plausible version of the planet, not measurements, which is why the scene is labelled 'inferred from data'.
Treat it as a thought experiment: what it might be like to stand on a planet where the sea has no shore. If future observations show that Kepler-22b is a gas-rich mini-Neptune, there would be no surface to stand on at all, but water worlds may still exist elsewhere among the many planets of its size.
Surprising facts about An ocean world
- Kepler-22b has never been seen directly: it is known only from a regular dip of about 0.05% in its star's light.
- Planets between the size of Earth and Neptune are among the most common in our galaxy, yet our Solar System has none.
- A true water world might have an ocean hundreds of kilometres deep, floored by ice that forms under enormous pressure.
- Being in the habitable zone means liquid water is possible, not that the planet is habitable.
- Kepler watched about 150,000 stars at once and found more than 2,600 confirmed planets.
- Most planetary systems are not lined up for us to see transits, so the transit method misses most planets.
Frequently asked questions
- Is Kepler-22b really covered in water?
- Nobody knows. Its size fits a water world, but it could equally be a mini-Neptune with a thick hydrogen and helium atmosphere and no solid surface. Its mass, which would help decide, has not been measured precisely.
- How far away is Kepler-22b?
- About 600–640 light years, in the direction of the constellations Cygnus and Lyra. Light from its star set off towards us around the late 14th or early 15th century.
- How was Kepler-22b discovered?
- By NASA's Kepler space telescope, using the transit method. Kepler detected a small, repeating dip in the star's brightness each time the planet passed in front of it, and the discovery was announced in December 2011.
- Could anything live there?
- We cannot say. Kepler-22b lies in its star's habitable zone, but whether it has liquid water, a suitable atmosphere or a surface at all is unknown.
- Can I explore Kepler-22b in the app?
- Yes, as an impression. You can land on a lone rock islet in an imagined ocean on Kepler-22b and explore it in interactive 3D. The scene is labelled 'inferred from data' because the surface itself has never been observed.
Keep exploring
- Land in the 3D ocean world landscape and walk around
- Jungle: layered rainforest, a muddy river and drifting spores
- Desert: wind-carved dunes with sharp crests and long shadows
- Glacier: a river of blue ice between granite peaks
- Volcano: black lava fields, a glowing lava lake and steaming vents
- Tropical beach & reef: white sand, leaning palms and a lagoon to dive into
- Ocean & underwater: dive the blue onto a reef-capped seamount full of life
- Savanna: golden grass, umbrella acacias, granite kopjes and herds
- Archipelago: ice-polished granite skerries and pine islets in calm baltic water
- Taiga (boreal forest): spruce forest on mossy moraine, mushrooms, deer and birdsong
- Finnish Lakeland: a midsummer evening over forested islands and calm blue lakes
- Grand Canyon: two billion years of rock layers, carved a mile deep
- Zhangye Danxia: rainbow-striped hills of tilted red sandstone
- Fjords: a deep glacial fjord between kilometre-high walls and waterfalls
- Arctic tundra: a wide treeless valley under the midnight sun, with reindeer and arctic foxes
- Alpine meadow: flower meadows, a mountain tarn and the matterhorn's pyramid
- Deciduous forest: maple, oak and beech in full autumn colour on misty blue ridges
- Prairie & grassland: a wide grassy valley where bison graze and wolves roam
- Okavango Delta: clear channels, papyrus and palm islands in a desert-fed wetland
- Australian outback: red sand, spinifex and desert oaks around uluṟu
- Mediterranean coast: maquis, olive and umbrella pine over a clear blue cove
- Bamboo forest: misty mountain bamboo thickets, home of the giant panda
- Antarctic coast: an emperor penguin colony on the sea ice, below towering ice-shelf cliffs
- Rice terraces of Bali: stepped paddies, coconut palms and ducks in the shallow water
- Hạ Long Bay: limestone towers rising from an emerald sea
- Mount Fuji: cherry blossom on the lakeshore, fuji's snowy cone beyond
- Himalaya: a turquoise lake below the world's highest peaks
- Great Barrier Reef: a coral cay, a vast reef flat and turtles in the shallows
- Lake Como: villas, cypresses and mountains around a deep blue lake
- Icelandic highlands: rainbow rhyolite hills, black lava and steaming springs
- Banff National Park: a turquoise lake under the valley of the ten peaks
- Iguazú Falls: hundreds of waterfalls thundering into a jungle gorge
- Torres del Paine: granite horns, turquoise lakes and wind-bent steppe
- The Moon's surface: grey regolith, craters and earth in a black sky
- Mars surface: rust-red plains, an ancient river delta and dust devils
- Europa's ice: cracked ice ridges under a sky filled by jupiter
- Io's lava plains: sulphur plains, lava lakes and plumes under a sky filled by jupiter
- Titan's methane shore: orange haze, dark methane seas and air thick enough to fly in
- Gas giant clouds: drifting cloud decks, lightning and a giant storm
The landscapes in Ember’s Universe are procedural 3D scenes modelled on real places. The landforms, plants and light follow the real thing, but the details are generated, not mapped.