TOI-663 c
TOI-663 c is a mini-Neptune orbiting the M1 V star TOI-663 in the constellation Sextans. It lies about 210 light-years from Earth and was discovered in 2024 using the transit method.
How Big Is TOI-663 c?
TOI-663 c has a radius of 2.26 times that of Earth. Its mass is 3.7 times that of Earth, giving it a density of 1.73 g/cm³ — closer to gas planets like Jupiter (1.33 g/cm³).
Is TOI-663 c in the Habitable Zone?
TOI-663 c orbits inside the inner edge of the habitable zone of TOI-663. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-663: 0.170–0.436 AU (conservative: 0.215–0.413 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-663 c
The equilibrium temperature of TOI-663 c 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 22.30 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-663 c — one full orbit around TOI-663 — lasts 4.70 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.044 AU — closer to its star than Mercury is to the Sun.
How Was TOI-663 c Discovered?
TOI-663 c was discovered in 2024 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-663 c?
TOI-663 c is 209.5 light-years (64.2 parsecs) from Earth. Light arriving here tonight left the planet around the year 1817. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,687,200 years to make the journey.
The Host Star: TOI-663
TOI-663
- Spectral type
- M1 V
- Surface temperature
- 3,681 K (Sun: 5,772 K)
- Mass
- 0.51 M☉
- Radius
- 0.51 R☉
The TOI-663 Planetary System
TOI-663 c is one of 3 known planets in the TOI-663 system. Its siblings:
TOI-663 c — Complete Data
| Radius | 2.260 Earth radii (0.202 Jupiter radii) |
|---|---|
| Mass | 3.65 Earth masses (0.011 Jupiter masses) |
| Density | 1.73 g/cm³ (Earth: 5.51) |
| Orbital period | 4.70 days |
| Orbital distance | 0.044 AU |
| Equilibrium temperature | 553 K (280 °C) |
| Stellar irradiation | 22.30× Earth |
| Distance from Earth | 209.5 light-years (64.2 parsecs) |
| Constellation | Sextans |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2024 |
Data: NASA Exoplanet Archive, last updated 2024-06-25. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-663 c
Is TOI-663 c habitable?
No — TOI-663 c orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-663 c?
TOI-663 c is about 210 light-years from Earth in the constellation Sextans. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,687,200 years to get there.
How big is TOI-663 c compared to Earth?
TOI-663 c has 2.26 times the radius of Earth and about 3.7 times its mass.
How long is a year on TOI-663 c?
One orbit around TOI-663 takes 4.7 Earth days — short enough that 78 of its years would fit into one Earth year.
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