TOI-5261 b
TOI-5261 b is a hot Jupiter orbiting TOI-5261 in the constellation Delphinus. It lies about 1,230 light-years from Earth and was discovered in 2025 using the transit method.
How Big Is TOI-5261 b?
TOI-5261 b has a radius of 11.60 times that of Earth, or 1.03 times the radius of Jupiter. Its mass is 3,652 times that of Earth, giving it a density of 12.90 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is TOI-5261 b in the Habitable Zone?
TOI-5261 b orbits inside the inner edge of the habitable zone of TOI-5261. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-5261: 0.768–1.809 AU (conservative: 0.973–1.715 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-5261 b
The equilibrium temperature of TOI-5261 b is about 1,244 K (971 °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.
Orbit and Year Length
A year on TOI-5261 b — one full orbit around TOI-5261 — lasts 4.15 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.051 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.16).
How Was TOI-5261 b Discovered?
TOI-5261 b was discovered in 2025 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-5261 b?
TOI-5261 b is 1,229.8 light-years (377.1 parsecs) from Earth. Light arriving here tonight left the planet about 1,230 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 21,644,480 years to make the journey.
The Host Star: TOI-5261
TOI-5261
- Surface temperature
- 5,790 K (Sun: 5,772 K)
- Mass
- 1.04 M☉
- Radius
- 1.02 R☉
- Luminosity
- 1.0490 L☉
- Age
- 4.2 billion years (Sun: 4.6)
Planetary System
TOI-5261 b is the only planet known to orbit TOI-5261 so far.
TOI-5261 b — Complete Data
| Radius | 11.601 Earth radii (1.035 Jupiter radii) |
|---|---|
| Mass | 3,651.85 Earth masses (11.490 Jupiter masses) |
| Density | 12.90 g/cm³ (Earth: 5.51) |
| Orbital period | 4.15 days |
| Orbital distance | 0.051 AU |
| Eccentricity | 0.159 |
| Equilibrium temperature | 1,244 K (971 °C) |
| Distance from Earth | 1,229.8 light-years (377.1 parsecs) |
| Constellation | Delphinus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2025 |
Data: NASA Exoplanet Archive, last updated 2025-09-25. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-5261 b
Is TOI-5261 b habitable?
No — TOI-5261 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-5261 b?
TOI-5261 b is about 1,230 light-years from Earth in the constellation Delphinus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 21,644,480 years to get there.
How big is TOI-5261 b compared to Earth?
TOI-5261 b has 11.60 times the radius of Earth and about 3,652 times its mass.
How long is a year on TOI-5261 b?
One orbit around TOI-5261 takes 4.2 Earth days — short enough that 88 of its years would fit into one Earth year.
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