TOI-139 b
TOI-139 b is a mini-Neptune orbiting TOI-139 in the constellation Piscis Austrinus. It lies about 138 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is TOI-139 b?
TOI-139 b has a radius of 2.46 times that of Earth.
Is TOI-139 b in the Habitable Zone?
The position of TOI-139 b relative to the habitable zone of TOI-139 cannot be precisely determined from the available orbital data.
Habitable zone of TOI-139: 0.350–0.861 AU (conservative: 0.443–0.816 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-139 b
The equilibrium temperature of TOI-139 b is about 561 K (288 °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 TOI-139 b — one full orbit around TOI-139 — lasts 11.1 Earth days, shorter than Mercury's 88-day year.
How Was TOI-139 b Discovered?
TOI-139 b was discovered in 2023 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-139 b?
TOI-139 b is 138.3 light-years (42.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1888. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,434,080 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-139 b scores 0.29, ranking #1,972 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-139
TOI-139
- Surface temperature
- 4,570 K (Sun: 5,772 K)
- Mass
- 0.69 M☉
- Radius
- 0.70 R☉
Planetary System
TOI-139 b is the only planet known to orbit TOI-139 so far.
TOI-139 b — Complete Data
| Radius | 2.457 Earth radii (0.219 Jupiter radii) |
|---|---|
| Orbital period | 11.07 days |
| Equilibrium temperature | 561 K (288 °C) |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 138.3 light-years (42.4 parsecs) |
| Constellation | Piscis Austrinus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2023-05-26. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-139 b
Is TOI-139 b habitable?
TOI-139 b is not known to orbit within the habitable zone of TOI-139, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is TOI-139 b?
TOI-139 b is about 138 light-years from Earth in the constellation Piscis Austrinus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,434,080 years to get there.
How big is TOI-139 b compared to Earth?
TOI-139 b has 2.46 times the radius of Earth.
How long is a year on TOI-139 b?
One orbit around TOI-139 takes 11.1 Earth days — short enough that 33 of its years would fit into one Earth year.
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