Kepler-1921 b
Kepler-1921 b is a mini-Neptune orbiting Kepler-1921 in the constellation Cygnus. It lies about 3,030 light-years from Earth and was discovered in 2021 using the transit method.
How Big Is Kepler-1921 b?
Kepler-1921 b has a radius of 2.89 times that of Earth.
Is Kepler-1921 b in the Habitable Zone?
The position of Kepler-1921 b relative to the habitable zone of Kepler-1921 cannot be precisely determined from the available orbital data.
Habitable zone of Kepler-1921: 1.649–3.854 AU (conservative: 2.089–3.654 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-1921 b — one full orbit around Kepler-1921 — lasts 20.0 Earth days, shorter than Mercury's 88-day year.
How Was Kepler-1921 b Discovered?
Kepler-1921 b was discovered in 2021 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-1921 b?
Kepler-1921 b is 3,030.0 light-years (929.0 parsecs) from Earth. Light arriving here tonight left the planet about 3,030 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 53,328,000 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-1921 b scores 0.22, ranking #3,673 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-1921
Kepler-1921
- Surface temperature
- 6,120 K (Sun: 5,772 K)
- Mass
- 1.25 M☉
- Radius
- 2.00 R☉
The Kepler-1921 Planetary System
Kepler-1921 b is one of 2 known planets in the Kepler-1921 system. Its siblings:
- Kepler-1921 c (Lava World)
Kepler-1921 b — Complete Data
| Radius | 2.895 Earth radii (0.258 Jupiter radii) |
|---|---|
| Orbital period | 20.03 days |
| Earth Similarity Index | 0.22 |
| Distance from Earth | 3,030.0 light-years (929.0 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-12-05. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-1921 b
Is Kepler-1921 b habitable?
Kepler-1921 b is not known to orbit within the habitable zone of Kepler-1921, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is Kepler-1921 b?
Kepler-1921 b is about 3,030 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 53,328,000 years to get there.
How big is Kepler-1921 b compared to Earth?
Kepler-1921 b has 2.89 times the radius of Earth.
How long is a year on Kepler-1921 b?
One orbit around Kepler-1921 takes 20.0 Earth days — short enough that 18 of its years would fit into one Earth year.
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