Kepler-33 d
Kepler-33 d is a Neptune-like planet orbiting Kepler-33 in the constellation Cygnus. It lies about 3,944 light-years from Earth and was discovered in 2011 using the transit method.
How Big Is Kepler-33 d?
Kepler-33 d has a radius of 5.35 times that of Earth.
Is Kepler-33 d in the Habitable Zone?
Kepler-33 d orbits inside the inner edge of the habitable zone of Kepler-33. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-33: 1.413–3.317 AU (conservative: 1.789–3.145 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on Kepler-33 d — one full orbit around Kepler-33 — lasts 21.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.166 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-33 d Discovered?
Kepler-33 d 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-33 d?
Kepler-33 d is 3,943.7 light-years (1,209.2 parsecs) from Earth. Light arriving here tonight left the planet about 3,944 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 69,409,120 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-33 d scores 0.15, ranking #4,201 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-33
Kepler-33
- Surface temperature
- 5,904 K (Sun: 5,772 K)
- Mass
- 1.29 M☉
- Radius
- 1.82 R☉
- Luminosity
- 3.5975 L☉
- Age
- 4.3 billion years (Sun: 4.6)
The Kepler-33 Planetary System
Kepler-33 d is one of 5 known planets in the Kepler-33 system. Its siblings:
- Kepler-33 b (Super Earth)
- Kepler-33 c (Sub Neptune)
- Kepler-33 e (Neptune-like)
- Kepler-33 f (Neptune-like)
Kepler-33 d — Complete Data
| Radius | 5.350 Earth radii (0.477 Jupiter radii) |
|---|---|
| Orbital period | 21.78 days |
| Orbital distance | 0.166 AU |
| Earth Similarity Index | 0.15 |
| Distance from Earth | 3,943.7 light-years (1,209.2 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2011 |
Data: NASA Exoplanet Archive, last updated 2021-10-04. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-33 d
Is Kepler-33 d habitable?
No — Kepler-33 d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-33 d?
Kepler-33 d is about 3,944 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 69,409,120 years to get there.
How big is Kepler-33 d compared to Earth?
Kepler-33 d has 5.35 times the radius of Earth.
How long is a year on Kepler-33 d?
One orbit around Kepler-33 takes 21.8 Earth days — short enough that 17 of its years would fit into one Earth year.
Explore Kepler-33 d in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
