TOI-6478 b
TOI-6478 b is a Neptune-like planet orbiting the M4.0+/-0.5 star TOI-6478 in the constellation Hydra. It lies about 126 light-years from Earth and was discovered in 2025 using the transit method. It orbits within the habitable zone of its star — the region where liquid water could exist on a planet's surface.
How Big Is TOI-6478 b?
TOI-6478 b has a radius of 4.60 times that of Earth.
Is TOI-6478 b in the Habitable Zone?
TOI-6478 b orbits inside the conservative habitable zone of TOI-6478 — the region where a rocky planet could sustain liquid water on its surface. This makes it one of the most interesting known exoplanets in the search for life.
Habitable zone of TOI-6478: 0.060–0.158 AU (conservative: 0.076–0.150 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Temperature on TOI-6478 b
The equilibrium temperature of TOI-6478 b is about 204 K (-69 °C) — well below freezing. 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-6478 b — one full orbit around TOI-6478 — lasts 34.0 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.114 AU — closer to its star than Mercury is to the Sun.
How Was TOI-6478 b Discovered?
TOI-6478 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-6478 b?
TOI-6478 b is 125.9 light-years (38.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1901. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,215,840 years to make the journey.
The Host Star: TOI-6478
TOI-6478 b belongs to a system of 2 stars; it orbits TOI-6478.
TOI-6478
- Spectral type
- M4.0+/-0.5
- Surface temperature
- 3,230 K (Sun: 5,772 K)
- Mass
- 0.23 M☉
- Radius
- 0.23 R☉
- Age
- 6.0 billion years (Sun: 4.6)
Planetary System
TOI-6478 b is the only planet known to orbit TOI-6478 so far.
TOI-6478 b — Complete Data
| Radius | 4.600 Earth radii (0.411 Jupiter radii) |
|---|---|
| Orbital period | 34.01 days |
| Orbital distance | 0.114 AU |
| Equilibrium temperature | 204 K (-69 °C) |
| Distance from Earth | 125.9 light-years (38.6 parsecs) |
| Constellation | Hydra |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2025 |
Data: NASA Exoplanet Archive, last updated 2025-04-29. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-6478 b
Is TOI-6478 b habitable?
TOI-6478 b orbits within the habitable zone of TOI-6478, the region where liquid water could exist on a planet's surface. It sits in the conservative habitable zone — the most promising region for habitability. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is TOI-6478 b?
TOI-6478 b is about 126 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,215,840 years to get there.
How big is TOI-6478 b compared to Earth?
TOI-6478 b has 4.60 times the radius of Earth.
How long is a year on TOI-6478 b?
One orbit around TOI-6478 takes 34.0 Earth days — short enough that 11 of its years would fit into one Earth year.
Explore TOI-6478 b in the app
Browse, filter and compare 6,000+ exoplanets on iPhone, iPad and Apple Watch — with habitable-zone views, widgets and offline data.
