About the image. Drawn as a global ocean with storm systems, one of the ideas proposed for this planet. Its radius is measured; its mass is only an upper limit and its surface is unknown.
1.1×as wide as our Sun, almost exactly
≈ 1×about as much light as Earth gets
The sky from Kepler-22b
Kepler-22 would look 1.1× as wide as the Sun does from Earth, almost exactly like our Sun, and the planet gets about as much light as Earth gets from the Sun.
Its colour comes from its surface temperature of 5 596 K (5 320 °C); the Sun's is about 5 772 K (5 500 °C).
How fast Kepler-22b 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 5 December 2011 the Kepler team announced the first known transiting planet orbiting inside the habitable zone of a Sun-like star: the band of orbits where a planet with the right atmosphere could keep liquid water on its surface. Kepler-22b circles its star every 290 days, a little closer in than Earth.
A water world?
The planet is about twice as wide as Earth. Its mass has never been pinned down. Radial-velocity measurements, which look for the star’s wobble, only show that it is lighter than about 9.1 Earth masses. Even that limit rules out an Earth-like rocky composition, at least at the one-sigma level, so the planet is more likely to be rich in water or gas.
That is why it is often called a possible ocean world: a deep global sea over a small rocky core. Kepler scientist Natalie Batalha remarked at the time that life in such an ocean was “not beyond the realm of possibility”. It could just as well be a small gassy planet with no surface at all.
Why it still matters
Kepler-22b was the proof that planets of roughly this size, in roughly this kind of orbit, around stars like ours, exist. Many more have been found since, but this was the first.
Its orbit, to scale
Kepler-22b goes around once every 290 days, at 0.812 AU from its star. Dashed circles show Mercury, Venus around the Sun, on the same scale.
Kepler-22b: equilibrium temperature. Logarithmic scale from 100 K to 10 000 K. Reference values: NASA, IAU.
How long to get there?
Kepler-22b is about 635 light-years away.
Light299 792 km/s635 years
Breakthrough Starshotplanned light sail, 20% of light speed3 175 years
Parker Solar Probefastest spacecraft so far, 192 km/s991 500 years
Voyager 1leaving the Solar System, 17 km/s11.2 million years
At Voyager 1's speed the trip would take about 139 976 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Gallery
Artist's impressions rendered from the same model as the view at the top of this page.
Timeline
2009Kepler records the first transit of the planet across its star.
2011Announced as the first transiting planet in the habitable zone of a Sun-like star.
2023Radial-velocity data cap its mass at about 9.1 Earth masses.
Questions people ask
Is Kepler-22b an ocean planet?
It might be. Its size and mass limit rule out an Earth-like rocky make-up, so it is probably rich in water or gas. A global ocean is one possibility; a small gas-wrapped planet is another.
Could Kepler-22b support life?
It orbits in its star's habitable zone, but its surface is unknown. If it is an ocean world, scientists have said life in such an ocean is not impossible.