Kepler-17 b
Kepler-17 b is a hot Jupiter orbiting Kepler-17 in the constellation Cygnus. It lies about 2,351 light-years from Earth and was discovered in 2011 using the transit method.
How Big Is Kepler-17 b?
Kepler-17 b has a radius of 14.68 times that of Earth, or 1.31 times the radius of Jupiter. Its mass is 779 times that of Earth, giving it a density of 1.35 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-17 b in the Habitable Zone?
Kepler-17 b orbits inside the inner edge of the habitable zone of Kepler-17. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-17: 0.760–1.791 AU (conservative: 0.963–1.698 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-17 b
The equilibrium temperature of Kepler-17 b is about 1,570 K (1,297 °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-17 b — one full orbit around Kepler-17 — lasts just 35.7 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.026 AU — closer to its star than Mercury is to the Sun. Its orbit is nearly circular (eccentricity 0.011).
How Was Kepler-17 b Discovered?
Kepler-17 b was discovered in 2011 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-17 b?
Kepler-17 b is 2,350.8 light-years (720.8 parsecs) from Earth. Light arriving here tonight left the planet about 2,351 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 41,374,080 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-17 b scores 0.06, ranking #5,115 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-17
Kepler-17
- Surface temperature
- 5,781 K (Sun: 5,772 K)
- Mass
- 1.04 M☉
- Radius
- 1.01 R☉
- Luminosity
- 1.0272 L☉
Planetary System
Kepler-17 b is the only planet known to orbit Kepler-17 so far.
Kepler-17 b — Complete Data
| Radius | 14.680 Earth radii (1.310 Jupiter radii) |
|---|---|
| Mass | 778.65 Earth masses (2.450 Jupiter masses) |
| Density | 1.35 g/cm³ (Earth: 5.51) |
| Orbital period | 1.49 days |
| Orbital distance | 0.026 AU |
| Eccentricity | 0.011 |
| Equilibrium temperature | 1,570 K (1,297 °C) |
| Earth Similarity Index | 0.06 |
| Distance from Earth | 2,350.8 light-years (720.8 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2011 |
Data: NASA Exoplanet Archive, last updated 2019-12-02. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-17 b
Is Kepler-17 b habitable?
No — Kepler-17 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-17 b?
Kepler-17 b is about 2,351 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 41,374,080 years to get there.
How big is Kepler-17 b compared to Earth?
Kepler-17 b has 14.68 times the radius of Earth and about 779 times its mass.
How long is a year on Kepler-17 b?
One orbit around Kepler-17 takes 1.5 Earth days — short enough that 246 of its years would fit into one Earth year.
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