GJ 9827 b
GJ 9827 b is a super-Earth orbiting the K7 V star GJ 9827 in the constellation Pisces. It lies about 97 light-years from Earth and was discovered in 2017 using the transit method.
How Big Is GJ 9827 b?
GJ 9827 b has a radius of 1.44 times that of Earth. Its mass is 4.3 times that of Earth, giving it a density of 7.86 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is GJ 9827 b in the Habitable Zone?
GJ 9827 b orbits inside the inner edge of the habitable zone of GJ 9827. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 9827: 0.251–0.629 AU (conservative: 0.318–0.596 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 9827 b
The equilibrium temperature of GJ 9827 b is about 1,035 K (762 °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.
Orbit and Year Length
A year on GJ 9827 b — one full orbit around GJ 9827 — lasts just 29.0 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.019 AU — closer to its star than Mercury is to the Sun.
How Was GJ 9827 b Discovered?
GJ 9827 b was discovered in 2017 using the transit method, with observations from K2.
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 GJ 9827 b?
GJ 9827 b is 96.7 light-years (29.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1930. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,701,920 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. GJ 9827 b scores 0.29, ranking #2,051 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 9827
GJ 9827
- Spectral type
- K7 V
- Surface temperature
- 4,236 K (Sun: 5,772 K)
- Mass
- 0.62 M☉
- Radius
- 0.58 R☉
- Age
- 5.5 billion years (Sun: 4.6)
The GJ 9827 Planetary System
GJ 9827 b is one of 3 known planets in the GJ 9827 system. Its siblings:
GJ 9827 b — Complete Data
| Radius | 1.440 Earth radii (0.128 Jupiter radii) |
|---|---|
| Mass | 4.28 Earth masses (0.013 Jupiter masses) |
| Density | 7.86 g/cm³ (Earth: 5.51) |
| Orbital period | 1.21 days |
| Orbital distance | 0.019 AU |
| Equilibrium temperature | 1,035 K (762 °C) |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 96.7 light-years (29.7 parsecs) |
| Constellation | Pisces |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2025-01-09. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 9827 b
Is GJ 9827 b habitable?
No — GJ 9827 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 9827 b?
GJ 9827 b is about 97 light-years from Earth in the constellation Pisces. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,701,920 years to get there.
How big is GJ 9827 b compared to Earth?
GJ 9827 b has 1.44 times the radius of Earth and about 4.3 times its mass.
How long is a year on GJ 9827 b?
One orbit around GJ 9827 takes 1.2 Earth days — short enough that 302 of its years would fit into one Earth year.
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