Kepler-1987 d
Kepler-1987 d is a mini-Neptune orbiting Kepler-1987 in the constellation Cygnus. It lies about 1,943 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is Kepler-1987 d?
Kepler-1987 d has a radius of 2.66 times that of Earth.
Is Kepler-1987 d in the Habitable Zone?
Kepler-1987 d orbits inside the inner edge of the habitable zone of Kepler-1987. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-1987: 0.385–0.940 AU (conservative: 0.488–0.891 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on Kepler-1987 d
The equilibrium temperature of Kepler-1987 d is about 744 K (471 °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. It receives 72.38 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on Kepler-1987 d — one full orbit around Kepler-1987 — lasts 5.64 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.057 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-1987 d Discovered?
Kepler-1987 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-1987 d?
Kepler-1987 d is 1,942.9 light-years (595.7 parsecs) from Earth. Light arriving here tonight left the planet about 1,943 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 34,195,040 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-1987 d scores 0.24, ranking #3,297 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-1987
Kepler-1987
- Surface temperature
- 4,769 K (Sun: 5,772 K)
- Mass
- 0.80 M☉
- Radius
- 0.71 R☉
The Kepler-1987 Planetary System
Kepler-1987 d is one of 4 known planets in the Kepler-1987 system. Its siblings:
- Kepler-1987 b (Terrestrial)
- Kepler-1987 c (Super Earth)
- Kepler-1987 e (Super Earth)
Kepler-1987 d — Complete Data
| Radius | 2.660 Earth radii (0.237 Jupiter radii) |
|---|---|
| Orbital period | 5.64 days |
| Orbital distance | 0.057 AU |
| Equilibrium temperature | 744 K (471 °C) |
| Stellar irradiation | 72.38× Earth |
| Earth Similarity Index | 0.24 |
| Distance from Earth | 1,942.9 light-years (595.7 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-1987 d
Is Kepler-1987 d habitable?
No — Kepler-1987 d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-1987 d?
Kepler-1987 d is about 1,943 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 34,195,040 years to get there.
How big is Kepler-1987 d compared to Earth?
Kepler-1987 d has 2.66 times the radius of Earth.
How long is a year on Kepler-1987 d?
One orbit around Kepler-1987 takes 5.6 Earth days — short enough that 65 of its years would fit into one Earth year.
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