TOI-198 b
TOI-198 b is a super-Earth orbiting TOI-198 in the constellation Sculptor. It lies about 77 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is TOI-198 b?
TOI-198 b has a radius of 1.36 times that of Earth. Its mass is 3.2 times that of Earth, giving it a density of 6.89 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is TOI-198 b in the Habitable Zone?
TOI-198 b orbits inside the inner edge of the habitable zone of TOI-198. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-198: 0.147–0.377 AU (conservative: 0.187–0.357 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-198 b
The equilibrium temperature of TOI-198 b is about 456 K (183 °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 7.20 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-198 b — one full orbit around TOI-198 — lasts 10.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.068 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.15).
How Was TOI-198 b Discovered?
TOI-198 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-198 b?
TOI-198 b is 77.4 light-years (23.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1949. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,362,240 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-198 b scores 0.57, ranking #163 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-198
TOI-198
- Surface temperature
- 3,801 K (Sun: 5,772 K)
- Mass
- 0.42 M☉
- Radius
- 0.42 R☉
- Luminosity
- 0.0328 L☉
- Age
- 1.0 billion years (Sun: 4.6)
Planetary System
TOI-198 b is the only planet known to orbit TOI-198 so far.
TOI-198 b — Complete Data
| Radius | 1.360 Earth radii (0.121 Jupiter radii) |
|---|---|
| Mass | 3.17 Earth masses (0.010 Jupiter masses) |
| Density | 6.89 g/cm³ (Earth: 5.51) |
| Orbital period | 10.22 days |
| Orbital distance | 0.068 AU |
| Eccentricity | 0.150 |
| Equilibrium temperature | 456 K (183 °C) |
| Stellar irradiation | 7.20× Earth |
| Earth Similarity Index | 0.57 |
| Distance from Earth | 77.4 light-years (23.7 parsecs) |
| Constellation | Sculptor |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2026-04-09. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-198 b
Is TOI-198 b habitable?
No — TOI-198 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-198 b?
TOI-198 b is about 77 light-years from Earth in the constellation Sculptor. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,362,240 years to get there.
How big is TOI-198 b compared to Earth?
TOI-198 b has 1.36 times the radius of Earth and about 3.2 times its mass.
How long is a year on TOI-198 b?
One orbit around TOI-198 takes 10.2 Earth days — short enough that 36 of its years would fit into one Earth year.
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