TOI-1685 b
TOI-1685 b is a super-Earth orbiting the M3 V star TOI-1685 in the constellation Perseus. It lies about 123 light-years from Earth and was discovered in 2021 using the transit method.
How Big Is TOI-1685 b?
TOI-1685 b has a radius of 1.42 times that of Earth. Its mass is 3.1 times that of Earth.
Is TOI-1685 b in the Habitable Zone?
TOI-1685 b orbits inside the inner edge of the habitable zone of TOI-1685. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of TOI-1685: 0.136–0.354 AU (conservative: 0.173–0.336 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on TOI-1685 b
The equilibrium temperature of TOI-1685 b is about 1,000 K (727 °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 213 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on TOI-1685 b — one full orbit around TOI-1685 — lasts just 16.1 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.012 AU — closer to its star than Mercury is to the Sun.
How Was TOI-1685 b Discovered?
TOI-1685 b was discovered in 2021 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-1685 b?
TOI-1685 b is 122.7 light-years (37.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1904. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 2,159,520 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. TOI-1685 b scores 0.28, ranking #2,410 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-1685
TOI-1685
- Spectral type
- M3 V
- Surface temperature
- 3,470 K (Sun: 5,772 K)
- Mass
- 0.47 M☉
- Radius
- 0.46 R☉
- Age
- 1.4 billion years (Sun: 4.6)
Planetary System
TOI-1685 b is the only planet known to orbit TOI-1685 so far.
TOI-1685 b — Complete Data
| Radius | 1.421 Earth radii (0.127 Jupiter radii) |
|---|---|
| Mass | 3.07 Earth masses (0.010 Jupiter masses) |
| Orbital period | 0.67 days |
| Orbital distance | 0.012 AU |
| Equilibrium temperature | 1,000 K (727 °C) |
| Stellar irradiation | 213.00× Earth |
| Earth Similarity Index | 0.28 |
| Distance from Earth | 122.7 light-years (37.6 parsecs) |
| Constellation | Perseus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2025-11-20. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-1685 b
Is TOI-1685 b habitable?
No — TOI-1685 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is TOI-1685 b?
TOI-1685 b is about 123 light-years from Earth in the constellation Perseus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 2,159,520 years to get there.
How big is TOI-1685 b compared to Earth?
TOI-1685 b has 1.42 times the radius of Earth and about 3.1 times its mass.
How long is a year on TOI-1685 b?
One orbit around TOI-1685 takes 0.7 Earth days — short enough that 546 of its years would fit into one Earth year.
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