SPECULOOS-3 b
SPECULOOS-3 b is a terrestrial planet orbiting the M6.5+/-0.5 star SPECULOOS-3 in the constellation Cygnus. It was discovered in 2024 using the transit method.
How Big Is SPECULOOS-3 b?
SPECULOOS-3 b has a radius of 0.98 times that of Earth.
Is SPECULOOS-3 b in the Habitable Zone?
SPECULOOS-3 b orbits inside the inner edge of the habitable zone of SPECULOOS-3. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of SPECULOOS-3: 0.024–0.064 AU (conservative: 0.030–0.061 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on SPECULOOS-3 b
The equilibrium temperature of SPECULOOS-3 b is about 553 K (280 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 15.54 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on SPECULOOS-3 b — one full orbit around SPECULOOS-3 — lasts just 17.3 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.007 AU — closer to its star than Mercury is to the Sun.
How Was SPECULOOS-3 b Discovered?
SPECULOOS-3 b was discovered in 2024 using the transit method, with observations from SPECULOOS Southern Observatory.
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.
The Host Star: SPECULOOS-3
SPECULOOS-3
- Spectral type
- M6.5+/-0.5
- Surface temperature
- 2,800 K (Sun: 5,772 K)
- Mass
- 0.10 M☉
- Radius
- 0.12 R☉
- Luminosity
- 0.0008 L☉
- Age
- 6.6 billion years (Sun: 4.6)
Planetary System
SPECULOOS-3 b is the only planet known to orbit SPECULOOS-3 so far.
SPECULOOS-3 b — Complete Data
| Radius | 0.977 Earth radii (0.087 Jupiter radii) |
|---|---|
| Orbital period | 0.72 days |
| Orbital distance | 0.007 AU |
| Equilibrium temperature | 553 K (280 °C) |
| Stellar irradiation | 15.54× Earth |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | SPECULOOS Southern Observatory |
| Discovery year | 2024 |
Data: NASA Exoplanet Archive, last updated 2025-11-13. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About SPECULOOS-3 b
Is SPECULOOS-3 b habitable?
No — SPECULOOS-3 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How big is SPECULOOS-3 b compared to Earth?
SPECULOOS-3 b has 0.98 times the radius of Earth.
How long is a year on SPECULOOS-3 b?
One orbit around SPECULOOS-3 takes 0.7 Earth days — short enough that 508 of its years would fit into one Earth year.
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