Host star — Kepler-438
- Spectral type
- —
- Temperature
- 3,748 K
- Radius
- 0.52 R☉
- Mass
- 0.54 M☉
- Luminosity
- 0.044 L☉
- Distance
- 195.9 pc (639 ly)
Cooler than the Sun. Orange or red dwarf.
Kepler-438 b
Orbits Kepler-438 · 639 light-years from Earth
RockyTransit2015ESI 83 · Very Earth-like
Radius
1.12×
Earth
Mass
1.5×
Earth
Year
35d
Temp
288 K
15°C
Gravity
1.2×
Earth
Distance
639
ly
Could life exist here?
AI analysisKepler-438 b is a rocky world just 12 percent larger than Earth, orbiting a cool red dwarf star 639 light-years away. With an equilibrium temperature of 288 Kelvin—nearly identical to Earth's average surface temperature—and a nearly circular orbit at 0.166 astronomical units from its host star, this planet sits squarely in the habitable zone where liquid water could exist on its surface. Its mass of 1.46 Earth masses and density of 5.71 grams per cubic centimeter suggest a terrestrial composition similar to our own planet, though we cannot yet know if it has an atmosphere to retain heat or protect against radiation. The main unknowns are whether Kepler-438 b has retained a magnetic field and atmospheric shield over billions of years in close proximity to its star, and whether its 35.2-day year allows for climate stability. This planet achieved an exceptional habitability score of 83 out of 100, making it one of the most Earth-like worlds discovered to date via the transit method.
What it would be like
Kepler-438 b is a rocky world, potentially similar in composition to Earth or Mars — a solid surface you could, in theory, stand on.
Surface gravity is about 1.2g — noticeably heavier what you're used to on Earth.
With an equilibrium temperature around 15°C, this planet sits in the temperature range where liquid water could potentially exist on the surface — a key ingredient for life as we know it.
An orbital period of 35 days makes the year 10.4× shorter than Earth's. You'd celebrate your birthday more often here.
Earth comparison
Logarithmic bars so Jupiter-class planets fit the same scale as Earth-size worlds.
Radius1.12R⊕
1/25×Earth = 125×
Mass1.46M⊕
1/10000×Earth = 110000×
Surface gravity1.16g
1/100×Earth = 1100×
Equilibrium temp288 K(15°C)
0 KEarth 255 K2500 K
Side-by-side with Earth
Temperature in context
Liquid N₂Mars avgEarth eq.Earth sfc.Boiling H₂OVenus
Discovery & orbit
- Method
- Transit
- Year
- 2015
- Facility
- Kepler
- Semi-major axis
- 0.1660 AU
- Period
- 35.23 days
- Eccentricity
- 0.0300
- Density
- 5.71 g/cm³
Detected by measuring the tiny dip in starlight as the planet crosses in front of its star.
Mildly elliptical — similar to most Solar System planets.
Rocky composition likely. Earth is 5.51 g/cm³.
Discovered via · Transit
Tiny dip in starlight as the planet crosses in front of its star
A transit photometer watches a star nonstop and measures its brightness to ~0.01%. When a planet passes between us and the star, the star dims briefly — the deeper the dip, the bigger the planet. This is how Kepler and TESS found most known exoplanets.
- Overall share
- ~75% of all confirmed worlds
- Best for
- Earth-to-Neptune-sized planets on short orbits
Orbital Animation
Kepler-438Kepler-438 bOrbitHabitable zone
Drag to rotate · scroll to zoomSemi-major axis: 0.166 AUEccentricity: 0.0300Period: 35.2 days
Hertzsprung–Russell Diagram
Where this host star sits among … exoplanet host stars. The main sequence band runs diagonally — giants and supergiants sit above, white dwarfs below.
OBAFGKMCurrent star
How far is 639 light-years?
- A light beam leaving Earth right now would arrive in 639 years.
- At Voyager 1's speed (17 km/s), the trip would take approximately 11.3 million years.
- A radio signal sent today would arrive in 639.1 years — and the reply wouldn't come back for twice that.
Earth Similarity Index
83/1000 — Nothing like Earth100 — Identical to Earth
ESI combines radius similarity and equilibrium temperature similarity. Earth = 100. Mars ≈ 73. Venus ≈ 44. This score reflects two physical parameters only — not atmosphere, water, or magnetic field.