TOI-122 b
TOI-122 b is a mini-Neptune orbiting the M3 V star TOI-122 in the constellation Tucana. It lies about 203 light-years from Earth and was discovered in 2020 using the transit method.
How Big Is TOI-122 b?
TOI-122 b has a radius of 2.72 times that of Earth.
Is TOI-122 b in the Habitable Zone?
TOI-122 b orbits inside the inner edge of the habitable zone of TOI-122. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-122: 0.097–0.253 AU (conservative: 0.123–0.240 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 TOI-122 b
The equilibrium temperature of TOI-122 b is about 471 K (198 °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 8.80 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-122 b — one full orbit around TOI-122 — lasts 5.08 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.039 AU — closer to its star than Mercury is to the Sun.
How Was TOI-122 b Discovered?
TOI-122 b was discovered in 2020 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
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 TOI-122 b?
TOI-122 b is 202.6 light-years (62.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1824. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,565,760 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. TOI-122 b scores 0.35, ranking #801 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-122
TOI-122
- Spectral type
- M3 V
- Surface temperature
- 3,403 K (Sun: 5,772 K)
- Mass
- 0.31 M☉
- Radius
- 0.33 R☉
- Luminosity
- 0.0140 L☉
- Age
- 2.0 billion years (Sun: 4.6)
Planetary System
TOI-122 b is the only planet known to orbit TOI-122 so far.
TOI-122 b — Complete Data
| Radius | 2.720 Earth radii (0.243 Jupiter radii) |
|---|---|
| Orbital period | 5.08 days |
| Orbital distance | 0.039 AU |
| Equilibrium temperature | 471 K (198 °C) |
| Stellar irradiation | 8.80× Earth |
| Earth Similarity Index | 0.35 |
| Distance from Earth | 202.6 light-years (62.1 parsecs) |
| Constellation | Tucana |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2020 |
Data: NASA Exoplanet Archive, last updated 2020-12-10. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-122 b
Is TOI-122 b habitable?
No — TOI-122 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-122 b?
TOI-122 b is about 203 light-years from Earth in the constellation Tucana. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,565,760 years to get there.
How big is TOI-122 b compared to Earth?
TOI-122 b has 2.72 times the radius of Earth.
How long is a year on TOI-122 b?
One orbit around TOI-122 takes 5.1 Earth days — short enough that 72 of its years would fit into one Earth year.
Explore TOI-122 b in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
