Host star — TOI-2257
- Spectral type
- M3
- Temperature
- 3,430 K
- Radius
- 0.31 R☉
- Mass
- 0.33 M☉
- Luminosity
- 0.014 L☉
- Distance
- 57.8 pc (188 ly)
Red dwarf — the most common type of star. Cool and small.
Very cool — a faint red dwarf.
TOI-2257 b
Orbits TOI-2257 · 188 light-years from Earth
Super-EarthTransit2021ESI 87 · Very Earth-like
Radius
2.19×
Earth
Mass
5.5×
Earth
Year
35d
Temp
256 K
-17°C
Gravity
1.1×
Earth
Distance
188
ly
Could life exist here?
AI analysisTOI-2257 b is a super-Earth with 2.19 times Earth's radius and 5.45 Earth masses, orbiting a small, cool M3 star every 35.2 days at a distance of 0.145 AU. Its equilibrium temperature of 256 Kelvin sits well below Earth's average of 288 K—cold enough that the planet likely receives less stellar energy than our home world does. However, the planet's notably high density of 2.84 g/cm³ suggests a rocky composition with a substantial iron core, making it genuinely terrestrial rather than a gaseous world. The most significant complication is the planet's highly eccentric orbit of 0.496, which means its distance from the star swings dramatically, creating potentially extreme seasonal variations in temperature and radiation that could destabilize any developing biosphere. Its habitability score of 87 out of 100 reflects these trade-offs—a solid rocky world in a plausible orbital zone around its host, but with climatic volatility that remains poorly understood. TOI-2257 b's combination of substantial mass, genuine terrestrial character, and moderate distance from Earth (188 light-years) make it an exceptional target for atmospheric characterization with future telescopes.
What it would be like
TOI-2257 b is a super-Earth — larger than our planet but likely still rocky or ice-rich. Whether it has a thin atmosphere like Mars or a crushing one like Venus remains unknown.
Surface gravity is about 1.1g — noticeably heavier what you're used to on Earth.
With an equilibrium temperature around -17°C, this planet sits in the temperature range where liquid water could potentially exist on the surface — a key ingredient for life as we know it.
An orbital period of 35 days makes the year 10.4× shorter than Earth's. You'd celebrate your birthday more often here.
Earth comparison
Logarithmic bars so Jupiter-class planets fit the same scale as Earth-size worlds.
Radius2.19R⊕
1/25×Earth = 125×
Mass5.45M⊕
1/10000×Earth = 110000×
Surface gravity1.13g
1/100×Earth = 1100×
Equilibrium temp256 K(-17°C)
0 KEarth 255 K2500 K
Side-by-side with Earth
Temperature in context
Liquid N₂Mars avgEarth eq.Earth sfc.Boiling H₂OVenus
Discovery & orbit
- Method
- Transit
- Year
- 2021
- Facility
- Transiting Exoplanet Survey Satellite (TESS)
- Semi-major axis
- 0.1450 AU
- Period
- 35.19 days
- Eccentricity
- 0.4960
- Density
- 2.84 g/cm³
Detected by measuring the tiny dip in starlight as the planet crosses in front of its star.
Highly eccentric — temperatures would swing wildly between closest and farthest approach.
Low density — probably icy or gas-rich.
Discovered via · Transit
Tiny dip in starlight as the planet crosses in front of its star
A transit photometer watches a star nonstop and measures its brightness to ~0.01%. When a planet passes between us and the star, the star dims briefly — the deeper the dip, the bigger the planet. This is how Kepler and TESS found most known exoplanets.
- Overall share
- ~75% of all confirmed worlds
- Best for
- Earth-to-Neptune-sized planets on short orbits
Orbital Animation
TOI-2257TOI-2257 bOrbitHabitable zone
Drag to rotate · scroll to zoomSemi-major axis: 0.145 AUEccentricity: 0.4960Period: 35.2 days
Hertzsprung–Russell Diagram
Where this host star sits among … exoplanet host stars. The main sequence band runs diagonally — giants and supergiants sit above, white dwarfs below.
OBAFGKMCurrent star
How far is 188 light-years?
- A light beam leaving Earth right now would arrive in 188 years.
- At Voyager 1's speed (17 km/s), the trip would take approximately 3.3 million years.
- A radio signal sent today would arrive in 188.5 years — and the reply wouldn't come back for twice that.
Earth Similarity Index
87/1000 — Nothing like Earth100 — Identical to Earth
ESI combines radius similarity and equilibrium temperature similarity. Earth = 100. Mars ≈ 73. Venus ≈ 44. This score reflects two physical parameters only — not atmosphere, water, or magnetic field.