TOI-125 b
TOI-125 b is a mini-Neptune orbiting the K0 V star TOI-125 in the constellation Hydrus. It lies about 362 light-years from Earth and was discovered in 2019 using the transit method.
How Big Is TOI-125 b?
TOI-125 b has a radius of 2.73 times that of Earth. Its mass is 9.5 times that of Earth, giving it a density of 2.57 g/cm³ — between that of rocky and gaseous planets.
Is TOI-125 b in the Habitable Zone?
TOI-125 b orbits inside the inner edge of the habitable zone of TOI-125. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-125: 0.555–1.326 AU (conservative: 0.703–1.257 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-125 b
The equilibrium temperature of TOI-125 b is about 1,037 K (764 °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. It receives 185 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-125 b — one full orbit around TOI-125 — lasts 4.65 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.052 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.19).
How Was TOI-125 b Discovered?
TOI-125 b was discovered in 2019 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-125 b?
TOI-125 b is 362.2 light-years (111.1 parsecs) from Earth. Light arriving here tonight left the planet around the year 1664. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 6,374,720 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-125 b scores 0.23, ranking #3,546 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-125
TOI-125
- Spectral type
- K0 V
- Surface temperature
- 5,320 K (Sun: 5,772 K)
- Mass
- 0.86 M☉
- Radius
- 0.85 R☉
- Luminosity
- 0.5190 L☉
- Age
- 6.8 billion years (Sun: 4.6)
The TOI-125 Planetary System
TOI-125 b is one of 3 known planets in the TOI-125 system. Its siblings:
TOI-125 b — Complete Data
| Radius | 2.726 Earth radii (0.243 Jupiter radii) |
|---|---|
| Mass | 9.50 Earth masses (0.030 Jupiter masses) |
| Density | 2.57 g/cm³ (Earth: 5.51) |
| Orbital period | 4.65 days |
| Orbital distance | 0.052 AU |
| Eccentricity | 0.194 |
| Equilibrium temperature | 1,037 K (764 °C) |
| Stellar irradiation | 185.00× Earth |
| Earth Similarity Index | 0.23 |
| Distance from Earth | 362.2 light-years (111.1 parsecs) |
| Constellation | Hydrus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2020-02-06. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-125 b
Is TOI-125 b habitable?
No — TOI-125 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-125 b?
TOI-125 b is about 362 light-years from Earth in the constellation Hydrus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 6,374,720 years to get there.
How big is TOI-125 b compared to Earth?
TOI-125 b has 2.73 times the radius of Earth and about 9.5 times its mass.
How long is a year on TOI-125 b?
One orbit around TOI-125 takes 4.7 Earth days — short enough that 78 of its years would fit into one Earth year.
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