TOI-603 b
TOI-603 b is a cold gas giant orbiting the F8 IV star TOI-603 in the constellation Hydra. It lies about 672 light-years from Earth and was discovered in 2026 using the transit method.
How Big Is TOI-603 b?
TOI-603 b has a radius of 7.37 times that of Earth, or 0.66 times the radius of Jupiter. Its mass is 33.0 times that of Earth, giving it a density of 0.45 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is TOI-603 b in the Habitable Zone?
TOI-603 b orbits inside the inner edge of the habitable zone of TOI-603. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-603: 1.190–2.787 AU (conservative: 1.507–2.642 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-603 b
The equilibrium temperature of TOI-603 b is about 899 K (626 °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 157 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-603 b — one full orbit around TOI-603 — lasts 16.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.128 AU — closer to its star than Mercury is to the Sun.
How Was TOI-603 b Discovered?
TOI-603 b was discovered in 2026 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-603 b?
TOI-603 b is 671.6 light-years (205.9 parsecs) from Earth. Light arriving here tonight left the planet around the year 1355. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 11,820,160 years to make the journey.
The Host Star: TOI-603
TOI-603
- Spectral type
- F8 IV
- Surface temperature
- 6,027 K (Sun: 5,772 K)
- Mass
- 1.24 M☉
- Radius
- 1.48 R☉
- Luminosity
- 2.5920 L☉
Planetary System
TOI-603 b is the only planet known to orbit TOI-603 so far.
TOI-603 b — Complete Data
| Radius | 7.370 Earth radii (0.658 Jupiter radii) |
|---|---|
| Mass | 33.00 Earth masses (0.104 Jupiter masses) |
| Density | 0.45 g/cm³ (Earth: 5.51) |
| Orbital period | 16.18 days |
| Orbital distance | 0.128 AU |
| Equilibrium temperature | 899 K (626 °C) |
| Stellar irradiation | 157.00× Earth |
| Distance from Earth | 671.6 light-years (205.9 parsecs) |
| Constellation | Hydra |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2026 |
Data: NASA Exoplanet Archive, last updated 2026-08-20. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-603 b
Is TOI-603 b habitable?
No — TOI-603 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-603 b?
TOI-603 b is about 672 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 11,820,160 years to get there.
How big is TOI-603 b compared to Earth?
TOI-603 b has 7.37 times the radius of Earth and about 33.0 times its mass.
How long is a year on TOI-603 b?
One orbit around TOI-603 takes 16.2 Earth days — short enough that 23 of its years would fit into one Earth year.
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