Kepler-1661 b
Kepler-1661 b is a sub-Neptune orbiting the K star Kepler-1661 in the constellation Lyra. It lies about 1,339 light-years from Earth and was discovered in 2020 using the transit method. It orbits within the habitable zone of its star — the region where liquid water could exist on a planet's surface.
How Big Is Kepler-1661 b?
Kepler-1661 b has a radius of 3.87 times that of Earth. Its mass is 17.0 times that of Earth, giving it a density of 1.60 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is Kepler-1661 b in the Habitable Zone?
Kepler-1661 b orbits inside the conservative habitable zone of Kepler-1661 — the region where a rocky planet could sustain liquid water on its surface. This makes it one of the most interesting known exoplanets in the search for life.
Habitable zone of Kepler-1661: 0.463–1.114 AU (conservative: 0.586–1.057 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 ›
Temperature on Kepler-1661 b
The equilibrium temperature of Kepler-1661 b is about 243 K (-30 °C) — in a range broadly comparable to Earth, whose equilibrium temperature is 255 K. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 0.88 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-1661 b — one full orbit around Kepler-1661 — lasts 175.1 Earth days, between the years of Mercury (88 days) and Earth (365 days). It orbits at an average distance of 0.633 AU — comparable to the inner Solar System. Its orbit is mildly elliptical (eccentricity 0.06).
How Was Kepler-1661 b Discovered?
Kepler-1661 b was discovered in 2020 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-1661 b?
Kepler-1661 b is 1,339.2 light-years (410.6 parsecs) from Earth. Light arriving here tonight left the planet about 1,339 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 23,569,920 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-1661 b scores 0.57, ranking #166 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-1661
Kepler-1661 b is a circumbinary planet — it orbits around two stars at once, like Tatooine in Star Wars.
Kepler-1661
- Spectral type
- K
- Surface temperature
- 5,100 K (Sun: 5,772 K)
- Mass
- 0.84 M☉
- Radius
- 0.76 R☉
- Age
- 2.0 billion years (Sun: 4.6)
Planetary System
Kepler-1661 b is the only planet known to orbit Kepler-1661 so far.
Kepler-1661 b — Complete Data
| Radius | 3.870 Earth radii (0.345 Jupiter radii) |
|---|---|
| Mass | 17.00 Earth masses (0.053 Jupiter masses) |
| Density | 1.60 g/cm³ (Earth: 5.51) |
| Orbital period | 175.06 days |
| Orbital distance | 0.633 AU |
| Eccentricity | 0.057 |
| Equilibrium temperature | 243 K (-30 °C) |
| Stellar irradiation | 0.88× Earth |
| Earth Similarity Index | 0.57 |
| Distance from Earth | 1,339.2 light-years (410.6 parsecs) |
| Constellation | Lyra |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2020 |
Data: NASA Exoplanet Archive, last updated 2020-02-21. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-1661 b
Is Kepler-1661 b habitable?
Kepler-1661 b orbits within the habitable zone of Kepler-1661, the region where liquid water could exist on a planet's surface. It sits in the conservative habitable zone — the most promising region for habitability. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is Kepler-1661 b?
Kepler-1661 b is about 1,339 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 23,569,920 years to get there.
How big is Kepler-1661 b compared to Earth?
Kepler-1661 b has 3.87 times the radius of Earth and about 17.0 times its mass.
How long is a year on Kepler-1661 b?
One orbit around Kepler-1661 takes 175.1 Earth days.
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