Kepler-4 b
Kepler-4 b is a Neptune-like planet orbiting Kepler-4 in the constellation Draco. It lies about 1,591 light-years from Earth and was discovered in 2009 using the transit method.
How Big Is Kepler-4 b?
Kepler-4 b has a radius of 4.00 times that of Earth. Its mass is 24.5 times that of Earth, giving it a density of 1.91 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-4 b in the Habitable Zone?
Kepler-4 b orbits inside the inner edge of the habitable zone of Kepler-4. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-4: 1.123–2.640 AU (conservative: 1.422–2.503 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-4 b
The equilibrium temperature of Kepler-4 b is about 1,650 K (1,377 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on Kepler-4 b — one full orbit around Kepler-4 — lasts 3.21 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.046 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-4 b Discovered?
Kepler-4 b was discovered in 2009 using the transit method, with observations from Kepler.
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is Kepler-4 b?
Kepler-4 b is 1,591.4 light-years (487.9 parsecs) from Earth. Light arriving here tonight left the planet about 1,591 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 28,008,640 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. Kepler-4 b scores 0.18, ranking #4,059 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-4
Kepler-4
- Surface temperature
- 5,857 K (Sun: 5,772 K)
- Mass
- 1.22 M☉
- Radius
- 1.49 R☉
- Luminosity
- 2.2594 L☉
- Age
- 4.5 billion years (Sun: 4.6)
Planetary System
Kepler-4 b is the only planet known to orbit Kepler-4 so far.
Kepler-4 b — Complete Data
| Radius | 4.002 Earth radii (0.357 Jupiter radii) |
|---|---|
| Mass | 24.47 Earth masses (0.077 Jupiter masses) |
| Density | 1.91 g/cm³ (Earth: 5.51) |
| Orbital period | 3.21 days |
| Orbital distance | 0.046 AU |
| Equilibrium temperature | 1,650 K (1,377 °C) |
| Earth Similarity Index | 0.18 |
| Distance from Earth | 1,591.4 light-years (487.9 parsecs) |
| Constellation | Draco |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2009 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-4 b
Is Kepler-4 b habitable?
No — Kepler-4 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-4 b?
Kepler-4 b is about 1,591 light-years from Earth in the constellation Draco. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 28,008,640 years to get there.
How big is Kepler-4 b compared to Earth?
Kepler-4 b has 4.00 times the radius of Earth and about 24.5 times its mass.
How long is a year on Kepler-4 b?
One orbit around Kepler-4 takes 3.2 Earth days — short enough that 114 of its years would fit into one Earth year.
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