TOI-238 c
TOI-238 c is a mini-Neptune orbiting the K2 V star TOI-238 in the constellation Aquarius. It lies about 263 light-years from Earth and was discovered in 2024 using the radial velocity method.
How Big Is TOI-238 c?
TOI-238 c has a radius of 2.18 times that of Earth. Its mass is 6.7 times that of Earth, giving it a density of 1.83 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is TOI-238 c in the Habitable Zone?
TOI-238 c orbits inside the inner edge of the habitable zone of TOI-238. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-238: 0.453–1.092 AU (conservative: 0.573–1.035 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-238 c
The equilibrium temperature of TOI-238 c is about 696 K (423 °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 58.30 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-238 c — one full orbit around TOI-238 — lasts 8.47 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.075 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.36), swinging dramatically closer to and farther from its star.
How Was TOI-238 c Discovered?
TOI-238 c was discovered in 2024 using the radial velocity method, with observations from Multiple Observatories.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is TOI-238 c?
TOI-238 c is 262.7 light-years (80.5 parsecs) from Earth. Light arriving here tonight left the planet around the year 1764. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 4,623,520 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-238 c scores 0.27, ranking #2,716 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-238
TOI-238
- Spectral type
- K2 V
- Surface temperature
- 5,059 K (Sun: 5,772 K)
- Mass
- 0.78 M☉
- Radius
- 0.76 R☉
- Age
- 7.9 billion years (Sun: 4.6)
The TOI-238 Planetary System
TOI-238 c is one of 2 known planets in the TOI-238 system. Its siblings:
- TOI-238 b (Super Earth)
TOI-238 c — Complete Data
| Radius | 2.180 Earth radii (0.194 Jupiter radii) |
|---|---|
| Mass | 6.70 Earth masses (0.021 Jupiter masses) |
| Density | 1.83 g/cm³ (Earth: 5.51) |
| Orbital period | 8.47 days |
| Orbital distance | 0.075 AU |
| Eccentricity | 0.360 |
| Equilibrium temperature | 696 K (423 °C) |
| Stellar irradiation | 58.30× Earth |
| Earth Similarity Index | 0.27 |
| Distance from Earth | 262.7 light-years (80.5 parsecs) |
| Constellation | Aquarius |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2024 |
Data: NASA Exoplanet Archive, last updated 2024-02-16. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-238 c
Is TOI-238 c habitable?
No — TOI-238 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-238 c?
TOI-238 c is about 263 light-years from Earth in the constellation Aquarius. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 4,623,520 years to get there.
How big is TOI-238 c compared to Earth?
TOI-238 c has 2.18 times the radius of Earth and about 6.7 times its mass.
How long is a year on TOI-238 c?
One orbit around TOI-238 takes 8.5 Earth days — short enough that 43 of its years would fit into one Earth year.
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