GJ 720 A b
GJ 720 A b is a Neptune-like planet orbiting the M0.5 V star GJ 720 A in the constellation Lyra. It lies about 51 light-years from Earth and was discovered in 2021 using the radial velocity method.
Is GJ 720 A b in the Habitable Zone?
GJ 720 A b orbits inside the inner edge of the habitable zone of GJ 720 A. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 720 A: 0.200–0.511 AU (conservative: 0.254–0.485 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 720 A b
The equilibrium temperature of GJ 720 A b is about 401 K (128 °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.
Orbit and Year Length
A year on GJ 720 A b — one full orbit around GJ 720 A — lasts 19.5 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.119 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.12).
How Was GJ 720 A b Discovered?
GJ 720 A b was discovered in 2021 using the radial velocity method, with observations from Roque de los Muchachos Observatory.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is GJ 720 A b?
GJ 720 A b is 50.7 light-years (15.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1976. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 892,320 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 720 A b scores 0.40, ranking #482 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 720 A
GJ 720 A b belongs to a system of 2 stars; it orbits GJ 720 A.
GJ 720 A
- Spectral type
- M0.5 V
- Surface temperature
- 3,837 K (Sun: 5,772 K)
- Mass
- 0.57 M☉
- Radius
- 0.56 R☉
- Luminosity
- 0.0607 L☉
Planetary System
GJ 720 A b is the only planet known to orbit GJ 720 A so far.
GJ 720 A b — Complete Data
| Mass (best estimate) | 13.64 Earth masses |
|---|---|
| Orbital period | 19.47 days |
| Orbital distance | 0.119 AU |
| Eccentricity | 0.120 |
| Equilibrium temperature | 401 K (128 °C) |
| Earth Similarity Index | 0.40 |
| Distance from Earth | 50.7 light-years (15.6 parsecs) |
| Constellation | Lyra |
| Discovery method | Radial Velocity |
| Discovery facility | Roque de los Muchachos Observatory |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-07-12. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 720 A b
Is GJ 720 A b habitable?
No — GJ 720 A b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 720 A b?
GJ 720 A b is about 51 light-years from Earth in the constellation Lyra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 892,320 years to get there.
How long is a year on GJ 720 A b?
One orbit around GJ 720 A takes 19.5 Earth days — short enough that 19 of its years would fit into one Earth year.
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