A super-Earth candidate with a year longer than ours
Kepler-452b
Orbits Kepler-452 · 1,800 light-years · discovered 2015 (transit)
Kepler-452b orbits a Sun-like star about 1,800 light-years away in the constellation Cygnus. Its orbit takes about 385 days, only slightly longer than Earth's year, and it receives roughly 10% more energy from its star than Earth does from the Sun.
When NASA announced it in 2015, headlines dubbed it 'Earth 2.0' or 'Earth's cousin'. The reality is more uncertain. The planet is about 60% wider than Earth, its mass and composition are unknown, and some astronomers have argued that the evidence for it is not strong enough to call it confirmed.
Key facts
- Star
- Kepler-452G2V yellow dwarf
- Distance
- 1,800 light-years
- Radius
- 1.63 × Earth
- Mass
- Not measured
- Orbital period
- 384.8 days
- Equilibrium temperature
- 265 K (-8 °C)Before any greenhouse warming
- Starlight received
- 1.10× Earth's
- Surface gravity
- ≈ 1.92 gRough estimate (rocky composition assumed)
- Discovered
- 2015Transit
- Star
- Kepler-452 (G2V, Sun-like)
- Distance
- About 1,800 light-years
- Discovered
- 2015, transit (Kepler)
- Radius
- About 1.6 Earth radii
- Mass
- Not measured — estimated at roughly 5 Earth masses if rocky
- Orbital period
- About 385 days
- Starlight received
- Roughly 1.1 times what Earth gets from the Sun
- Equilibrium temperature
- About 265 K (−8 °C), a simple estimate that ignores any atmosphere
- Status
- Debated — some studies treat it as a candidate rather than a confirmed planet
Measured values follow the NASA Exoplanet Archive and discovery papers; many carry large uncertainties. The 3D globe and walkable surface on this page are an artist's impression generated from these numbers.
What we know
Kepler-452b is known from just a handful of transits in Kepler data, because its long orbit meant the spacecraft could catch it only about once a year. Those transits give a radius of roughly 1.6 Earth radii, though with sizeable uncertainty.
No mass has been measured. The discovery team estimated roughly 5 Earth masses if the planet is rocky, and judged it somewhat uncertain whether it is rocky at all. Planets of this size sit near the boundary between rocky super-Earths and gas-enveloped mini-Neptunes.
Its star
Kepler-452 is a G-type star of about the Sun's mass and temperature, though somewhat larger and brighter. It is thought to be around six billion years old — roughly 1.5 billion years older than the Sun — which offers a glimpse of what conditions might be like around a slightly older Sun-like star.
Could it be habitable?
Kepler-452b sits within its star's habitable zone, closer to the inner edge than Earth does. If it is rocky and has an atmosphere, it could have surface water — but because its ageing star is slowly brightening, some researchers have suggested it may be heading towards a runaway greenhouse, as Earth eventually will.
If instead it is a mini-Neptune with a thick hydrogen-rich envelope, it would not have a surface like Earth's. None of these possibilities has been tested by observation.
Orbit and climate
Kepler-452b orbits slightly farther from its star than Earth does from the Sun — just over one astronomical unit — taking about 385 days per orbit. On such a wide orbit it is unlikely to be tidally locked, so it could have a day–night cycle and seasons, but its rotation and tilt are unknown.
Discovery
A team led by Jon Jenkins of NASA's Ames Research Center announced Kepler-452b in July 2015, based on Kepler data and ground-based follow-up of the star. It was validated statistically rather than by measuring its mass.
A disputed planet
In 2018, a reanalysis of Kepler's final catalogue argued that the signal was too weak to rule out a false alarm and that Kepler-452b should be treated as a candidate. Later work has estimated a low false-positive probability, but the question has not been fully settled.
A revised distance
The original discovery estimated a distance of about 1,400 light-years. Precise parallax measurements from ESA's Gaia mission later placed the star at around 1,800 light-years.
Future observations
Kepler-452 is faint and distant, and the planet transits only about once a year, so confirming it independently is hard. Precise future measurements of the star — or a repeat detection of the transit by another telescope — would be needed to settle whether the planet is real and what it is made of.
About the 3D impression
Artist's impression — the real surface has never been seen. The globe and the surface you can walk on are generated from what is measured — size, the starlight it receives and the kind of star it orbits — using the same procedural engine as our imaginary worlds. Seas, ice, clouds and any plant-like colours are possibilities, not observations: around a red dwarf the daylight is redder, so the scene uses warmer skies and darker vegetation.
Earth-like exoplanets compared
| Planet | Distance | Radius | Year | Sunlight |
|---|---|---|---|---|
| Proxima Centauri b | 4.2 ly | — | 11.2 days | 0.65× Earth |
| Ross 128 b | 11.0 ly | — | 9.87 days | 1.38× Earth |
| Teegarden's Star b | 12.5 ly | — | 4.91 days | 1.08× Earth |
| Gliese 667 Cc | 23.6 ly | — | 28.1 days | 0.88× Earth |
| TRAPPIST-1d | 40.5 ly | 0.79 R⊕ | 4.05 days | 1.11× Earth |
| TRAPPIST-1e | 40.5 ly | 0.92 R⊕ | 6.10 days | 0.65× Earth |
| TRAPPIST-1f | 40.5 ly | 1.04 R⊕ | 9.21 days | 0.37× Earth |
| TRAPPIST-1g | 40.5 ly | 1.13 R⊕ | 12.4 days | 0.25× Earth |
| LHS 1140 b | 48.9 ly | 1.73 R⊕ | 24.7 days | 0.43× Earth |
| TOI-700 d | 101 ly | 1.07 R⊕ | 37.4 days | 0.87× Earth |
| Kepler-186f | 580 ly | 1.17 R⊕ | 129.9 days | 0.30× Earth |
| Kepler-22b | 635 ly | 2.10 R⊕ | 289.9 days | 1.01× Earth |
| Kepler-62f | 980 ly | 1.41 R⊕ | 267.3 days | 0.41× Earth |
| Kepler-442b | 1,194 ly | 1.34 R⊕ | 112.3 days | 0.70× Earth |
| Kepler-452b | 1,800 ly | 1.63 R⊕ | 384.8 days | 1.10× Earth |
Surprising facts about Kepler-452b
- A year on Kepler-452b lasts about 385 days — only around 20 days longer than Earth's.
- Its host star is thought to be about 1.5 billion years older than the Sun.
- Despite its 'Earth 2.0' nickname, the planet's very existence has been questioned by later studies.
- Kepler observed only a few transits of the planet over its four-year primary mission.