TOI-2128 b
TOI-2128 b is a mini-Neptune orbiting TOI-2128 in the constellation Hercules. It lies about 119 light-years from Earth and was discovered in 2024 using the transit method.
How Big Is TOI-2128 b?
TOI-2128 b has a radius of 2.09 times that of Earth. Its mass is 4.5 times that of Earth, giving it a density of 2.68 g/cm³ — between that of rocky and gaseous planets.
Is TOI-2128 b in the Habitable Zone?
TOI-2128 b orbits inside the inner edge of the habitable zone of TOI-2128. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-2128: 0.888–2.082 AU (conservative: 1.125–1.974 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-2128 b
The equilibrium temperature of TOI-2128 b is about 781 K (507 °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.
Orbit and Year Length
A year on TOI-2128 b — one full orbit around TOI-2128 — lasts 16.3 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.127 AU — closer to its star than Mercury is to the Sun.
How Was TOI-2128 b Discovered?
TOI-2128 b was discovered in 2024 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-2128 b?
TOI-2128 b is 119.3 light-years (36.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1907. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,099,680 years to make the journey.
The Host Star: TOI-2128
TOI-2128
- Surface temperature
- 5,968 K (Sun: 5,772 K)
- Mass
- 1.03 M☉
- Radius
- 1.12 R☉
- Luminosity
- 1.4330 L☉
- Age
- 4.7 billion years (Sun: 4.6)
Planetary System
TOI-2128 b is the only planet known to orbit TOI-2128 so far.
TOI-2128 b — Complete Data
| Radius | 2.089 Earth radii (0.186 Jupiter radii) |
|---|---|
| Mass | 4.50 Earth masses (0.014 Jupiter masses) |
| Density | 2.68 g/cm³ (Earth: 5.51) |
| Orbital period | 16.34 days |
| Orbital distance | 0.127 AU |
| Equilibrium temperature | 781 K (507 °C) |
| Distance from Earth | 119.3 light-years (36.6 parsecs) |
| Constellation | Hercules |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2024 |
Data: NASA Exoplanet Archive, last updated 2024-07-23. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-2128 b
Is TOI-2128 b habitable?
No — TOI-2128 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-2128 b?
TOI-2128 b is about 119 light-years from Earth in the constellation Hercules. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,099,680 years to get there.
How big is TOI-2128 b compared to Earth?
TOI-2128 b has 2.09 times the radius of Earth and about 4.5 times its mass.
How long is a year on TOI-2128 b?
One orbit around TOI-2128 takes 16.3 Earth days — short enough that 22 of its years would fit into one Earth year.
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