TOI-2257 b
TOI-2257 b is a mini-Neptune orbiting the M3 star TOI-2257 in the constellation Camelopardalis. It lies about 189 light-years from Earth and was discovered in 2021 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-2257 b?
TOI-2257 b has a radius of 2.19 times that of Earth.
Is TOI-2257 b in the Habitable Zone?
TOI-2257 b orbits inside the conservative habitable zone of TOI-2257 — 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-2257: 0.090–0.235 AU (conservative: 0.114–0.223 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-2257 b
The equilibrium temperature of TOI-2257 b is about 256 K (-17 °C) — in a range broadly comparable to Earth, whose equilibrium temperature is 255 K. 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-2257 b — one full orbit around TOI-2257 — lasts 35.2 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.145 AU — closer to its star than Mercury is to the Sun. Its orbit is highly elliptical (eccentricity 0.50), swinging dramatically closer to and farther from its star.
How Was TOI-2257 b Discovered?
TOI-2257 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-2257 b?
TOI-2257 b is 188.5 light-years (57.8 parsecs) from Earth. Light arriving here tonight left the planet around the year 1838. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 3,317,600 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-2257 b scores 0.72, ranking #52 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: TOI-2257
TOI-2257
- Spectral type
- M3
- Surface temperature
- 3,430 K (Sun: 5,772 K)
- Mass
- 0.33 M☉
- Radius
- 0.31 R☉
Planetary System
TOI-2257 b is the only planet known to orbit TOI-2257 so far.
TOI-2257 b — Complete Data
| Radius | 2.194 Earth radii (0.196 Jupiter radii) |
|---|---|
| Orbital period | 35.19 days |
| Orbital distance | 0.145 AU |
| Eccentricity | 0.496 |
| Equilibrium temperature | 256 K (-17 °C) |
| Earth Similarity Index | 0.72 |
| Distance from Earth | 188.5 light-years (57.8 parsecs) |
| Constellation | Camelopardalis |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-11-09. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About TOI-2257 b
Is TOI-2257 b habitable?
TOI-2257 b orbits within the habitable zone of TOI-2257, 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-2257 b?
TOI-2257 b is about 189 light-years from Earth in the constellation Camelopardalis. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 3,317,600 years to get there.
How big is TOI-2257 b compared to Earth?
TOI-2257 b has 2.19 times the radius of Earth.
How long is a year on TOI-2257 b?
One orbit around TOI-2257 takes 35.2 Earth days — short enough that 10 of its years would fit into one Earth year.
Explore TOI-2257 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.
