TOI-1203 b
TOI-1203 b is a super-Earth orbiting the G3 V star TOI-1203 in the constellation Hydra. It lies about 212 light-years from Earth and was discovered in 2025 using the radial velocity method.
How Big Is TOI-1203 b?
TOI-1203 b has a radius of 1.52 times that of Earth. Its mass is 3.5 times that of Earth, giving it a density of 5.48 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is TOI-1203 b in the Habitable Zone?
TOI-1203 b orbits inside the inner edge of the habitable zone of TOI-1203. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-1203: 0.874–2.062 AU (conservative: 1.108–1.955 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-1203 b
The equilibrium temperature of TOI-1203 b is about 1,361 K (1,088 °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 572 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-1203 b — one full orbit around TOI-1203 — lasts 4.16 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.049 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.07).
How Was TOI-1203 b Discovered?
TOI-1203 b was discovered in 2025 using the radial velocity method, with observations from La Silla Observatory.
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-1203 b?
TOI-1203 b is 212.0 light-years (65.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1814. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,731,200 years to make the journey.
The Host Star: TOI-1203
TOI-1203
- Spectral type
- G3 V
- Surface temperature
- 5,737 K (Sun: 5,772 K)
- Mass
- 0.89 M☉
- Radius
- 1.18 R☉
- Age
- 12.5 billion years (Sun: 4.6)
The TOI-1203 Planetary System
TOI-1203 b is one of 4 known planets in the TOI-1203 system. Its siblings:
- TOI-1203 c (Super Earth)
- TOI-1203 e (Neptune-like)
- TOI-1203.01 (Mini Neptune)
TOI-1203 b — Complete Data
| Radius | 1.520 Earth radii (0.136 Jupiter radii) |
|---|---|
| Mass | 3.51 Earth masses (0.011 Jupiter masses) |
| Density | 5.48 g/cm³ (Earth: 5.51) |
| Orbital period | 4.16 days |
| Orbital distance | 0.049 AU |
| Eccentricity | 0.067 |
| Equilibrium temperature | 1,361 K (1,088 °C) |
| Stellar irradiation | 572.20× Earth |
| Distance from Earth | 212.0 light-years (65.0 parsecs) |
| Constellation | Hydra |
| Discovery method | Radial Velocity |
| Discovery facility | La Silla Observatory |
| Discovery year | 2025 |
Data: NASA Exoplanet Archive, last updated 2025-10-02. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-1203 b
Is TOI-1203 b habitable?
No — TOI-1203 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-1203 b?
TOI-1203 b is about 212 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,731,200 years to get there.
How big is TOI-1203 b compared to Earth?
TOI-1203 b has 1.52 times the radius of Earth and about 3.5 times its mass.
How long is a year on TOI-1203 b?
One orbit around TOI-1203 takes 4.2 Earth days — short enough that 88 of its years would fit into one Earth year.
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