Kepler-347 d
Kepler-347 d is a sub-Neptune orbiting Kepler-347 in the constellation Cygnus. It lies about 4,236 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is Kepler-347 d?
Kepler-347 d has a radius of 3.04 times that of Earth.
Is Kepler-347 d in the Habitable Zone?
Kepler-347 d orbits inside the inner edge of the habitable zone of Kepler-347. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-347: 0.822–1.922 AU (conservative: 1.041–1.822 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-347 d
The equilibrium temperature of Kepler-347 d is about 482 K (209 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 12.75 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-347 d — one full orbit around Kepler-347 — lasts 85.5 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.380 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-347 d Discovered?
Kepler-347 d was discovered in 2023 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-347 d?
Kepler-347 d is 4,236.4 light-years (1,298.9 parsecs) from Earth. Light arriving here tonight left the planet about 4,236 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 74,560,640 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-347 d scores 0.28, ranking #2,086 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-347
Kepler-347
- Surface temperature
- 6,088 K (Sun: 5,772 K)
- Radius
- 1.00 R☉
The Kepler-347 Planetary System
Kepler-347 d is one of 3 known planets in the Kepler-347 system. Its siblings:
- Kepler-347 b (Super Earth)
- Kepler-347 c (Super Earth)
Kepler-347 d — Complete Data
| Radius | 3.040 Earth radii (0.271 Jupiter radii) |
|---|---|
| Orbital period | 85.52 days |
| Orbital distance | 0.380 AU |
| Equilibrium temperature | 482 K (209 °C) |
| Stellar irradiation | 12.75× Earth |
| Earth Similarity Index | 0.28 |
| Distance from Earth | 4,236.4 light-years (1,298.9 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2017-05-08. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-347 d
Is Kepler-347 d habitable?
No — Kepler-347 d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-347 d?
Kepler-347 d is about 4,236 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 74,560,640 years to get there.
How big is Kepler-347 d compared to Earth?
Kepler-347 d has 3.04 times the radius of Earth.
How long is a year on Kepler-347 d?
One orbit around Kepler-347 takes 85.5 Earth days.
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