G 9-40 b
G 9-40 b is a super-Earth orbiting G 9-40 in the constellation Cancer. It lies about 91 light-years from Earth and was discovered in 2019 using the transit method.
How Big Is G 9-40 b?
G 9-40 b has a radius of 1.90 times that of Earth. Its mass is 4.0 times that of Earth, giving it a density of 3.20 g/cm³ — between that of rocky and gaseous planets.
Is G 9-40 b in the Habitable Zone?
G 9-40 b orbits inside the inner edge of the habitable zone of G 9-40. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of G 9-40: 0.086–0.224 AU (conservative: 0.109–0.212 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on G 9-40 b
The equilibrium temperature of G 9-40 b is about 441 K (167 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 6.27 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on G 9-40 b — one full orbit around G 9-40 — lasts 5.75 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.042 AU — closer to its star than Mercury is to the Sun.
How Was G 9-40 b Discovered?
G 9-40 b was discovered in 2019 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 G 9-40 b?
G 9-40 b is 91.1 light-years (27.9 parsecs) from Earth. Light arriving here tonight left the planet around the year 1935. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,603,360 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. G 9-40 b scores 0.41, ranking #425 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: G 9-40
G 9-40
- Surface temperature
- 3,395 K (Sun: 5,772 K)
- Mass
- 0.30 M☉
- Radius
- 0.30 R☉
- Luminosity
- 0.0110 L☉
Planetary System
G 9-40 b is the only planet known to orbit G 9-40 so far.
G 9-40 b — Complete Data
| Radius | 1.900 Earth radii (0.170 Jupiter radii) |
|---|---|
| Mass | 4.00 Earth masses (0.013 Jupiter masses) |
| Density | 3.20 g/cm³ (Earth: 5.51) |
| Orbital period | 5.75 days |
| Orbital distance | 0.042 AU |
| Equilibrium temperature | 441 K (167 °C) |
| Stellar irradiation | 6.27× Earth |
| Earth Similarity Index | 0.41 |
| Distance from Earth | 91.1 light-years (27.9 parsecs) |
| Constellation | Cancer |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2024-10-22. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About G 9-40 b
Is G 9-40 b habitable?
No — G 9-40 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is G 9-40 b?
G 9-40 b is about 91 light-years from Earth in the constellation Cancer. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,603,360 years to get there.
How big is G 9-40 b compared to Earth?
G 9-40 b has 1.90 times the radius of Earth and about 4.0 times its mass.
How long is a year on G 9-40 b?
One orbit around G 9-40 takes 5.7 Earth days — short enough that 64 of its years would fit into one Earth year.
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