TOI-178 b
TOI-178 b is a terrestrial planet orbiting TOI-178 in the constellation Sculptor. It lies about 205 light-years from Earth and was discovered in 2021 using the transit method.
How Big Is TOI-178 b?
TOI-178 b has a radius of 1.20 times that of Earth. Its mass is 0.96 times that of Earth, giving it a density of 3.14 g/cm³ — between that of rocky and gaseous planets.
Is TOI-178 b in the Habitable Zone?
The position of TOI-178 b relative to the habitable zone of TOI-178 cannot be precisely determined from the available orbital data.
Habitable zone of TOI-178: 0.297–0.739 AU (conservative: 0.376–0.701 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 ›
Orbit and Year Length
A year on TOI-178 b — one full orbit around TOI-178 — lasts just 45.9 hours, shorter than Mercury's 88-day year.
How Was TOI-178 b Discovered?
TOI-178 b was discovered in 2021 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-178 b?
TOI-178 b is 204.5 light-years (62.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1822. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,599,200 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-178 b scores 0.30, ranking #1,427 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-178
TOI-178
- Surface temperature
- 4,316 K (Sun: 5,772 K)
- Mass
- 0.65 M☉
- Radius
- 0.66 R☉
- Luminosity
- 0.1360 L☉
- Age
- 6.0 billion years (Sun: 4.6)
The TOI-178 Planetary System
TOI-178 b is one of 6 known planets in the TOI-178 system. Its siblings:
TOI-178 b — Complete Data
| Radius | 1.200 Earth radii (0.107 Jupiter radii) |
|---|---|
| Mass | 0.96 Earth masses (0.003 Jupiter masses) |
| Density | 3.14 g/cm³ (Earth: 5.51) |
| Orbital period | 1.91 days |
| Earth Similarity Index | 0.30 |
| Distance from Earth | 204.5 light-years (62.7 parsecs) |
| Constellation | Sculptor |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2025-11-20. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-178 b
Is TOI-178 b habitable?
TOI-178 b is not known to orbit within the habitable zone of TOI-178, and as a terrestrial planet it is an unlikely candidate for life as we know it.
How far away is TOI-178 b?
TOI-178 b is about 205 light-years from Earth in the constellation Sculptor. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,599,200 years to get there.
How big is TOI-178 b compared to Earth?
TOI-178 b has 1.20 times the radius of Earth and about 0.96 times its mass.
How long is a year on TOI-178 b?
One orbit around TOI-178 takes 1.9 Earth days — short enough that 191 of its years would fit into one Earth year.
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