TOI-1238 b
TOI-1238 b is a terrestrial planet orbiting the K7/M0 star TOI-1238 in the constellation Draco. It lies about 231 light-years from Earth and was discovered in 2022 using the transit method.
How Big Is TOI-1238 b?
TOI-1238 b has a radius of 1.21 times that of Earth. Its mass is 3.8 times that of Earth, giving it a density of 11.70 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is TOI-1238 b in the Habitable Zone?
TOI-1238 b orbits inside the inner edge of the habitable zone of TOI-1238. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-1238: 0.233–0.587 AU (conservative: 0.295–0.556 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-1238 b
The equilibrium temperature of TOI-1238 b is about 1,133 K (860 °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 442 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-1238 b — one full orbit around TOI-1238 — lasts just 18.4 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.014 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.25).
How Was TOI-1238 b Discovered?
TOI-1238 b was discovered in 2022 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-1238 b?
TOI-1238 b is 230.6 light-years (70.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 1796. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,058,560 years to make the journey.
The Host Star: TOI-1238
TOI-1238
- Spectral type
- K7/M0
- Surface temperature
- 4,089 K (Sun: 5,772 K)
- Mass
- 0.59 M☉
- Radius
- 0.58 R☉
- Luminosity
- 0.0827 L☉
- Age
- 0.8 billion years (Sun: 4.6)
The TOI-1238 Planetary System
TOI-1238 b is one of 2 known planets in the TOI-1238 system. Its siblings:
- TOI-1238 c (Super Earth)
TOI-1238 b — Complete Data
| Radius | 1.210 Earth radii (0.108 Jupiter radii) |
|---|---|
| Mass | 3.76 Earth masses (0.012 Jupiter masses) |
| Density | 11.70 g/cm³ (Earth: 5.51) |
| Orbital period | 0.76 days |
| Orbital distance | 0.014 AU |
| Eccentricity | 0.250 |
| Equilibrium temperature | 1,133 K (860 °C) |
| Stellar irradiation | 442.00× Earth |
| Distance from Earth | 230.6 light-years (70.7 parsecs) |
| Constellation | Draco |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2022 |
Data: NASA Exoplanet Archive, last updated 2025-07-29. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-1238 b
Is TOI-1238 b habitable?
No — TOI-1238 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-1238 b?
TOI-1238 b is about 231 light-years from Earth in the constellation Draco. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,058,560 years to get there.
How big is TOI-1238 b compared to Earth?
TOI-1238 b has 1.21 times the radius of Earth and about 3.8 times its mass.
How long is a year on TOI-1238 b?
One orbit around TOI-1238 takes 0.8 Earth days — short enough that 478 of its years would fit into one Earth year.
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