Host star — Kepler-991
- Spectral type
- —
- Temperature
- 4,392 K
- Radius
- 0.61 R☉
- Mass
- 0.64 M☉
- Luminosity
- 0.148 L☉
- Distance
- 389.6 pc (1,271 ly)
Cooler than the Sun. Orange or red dwarf.
Kepler-991 b
Orbits Kepler-991 · 1,271 light-years from Earth
Neptune-likeTransit2016ESI 83 · Very Earth-like
Radius
2.54×
Earth
Mass
7.0×
Earth
Year
83d
Temp
260 K
-13°C
Gravity
1.1×
Earth
Distance
1,271
ly
Could life exist here?
AI analysisKepler-991 b orbits a cool, dimly glowing M-dwarf star at a distance of 0.31 AU, receiving enough stellar energy to maintain an equilibrium temperature of 260 Kelvin—roughly minus 13 degrees Celsius, or about as cold as Antarctica's interior. With a radius 2.54 times Earth's and a density of 2.34 g/cm³, this Neptune-like world likely retains a substantial atmosphere and possible water ice or even subsurface liquid water, though its exact composition remains unknown. Its circular 82.5-day orbit suggests orbital stability, a prerequisite for habitability. However, at 1,270 light-years away and discovered by the transit method in 2016, direct characterization of its atmosphere remains impossible with current technology, leaving critical questions unanswered: Is there a rocky surface beneath the atmosphere? Does liquid water exist? Could it be tidally locked to its star? The habitability score of 83 reflects these tantalizing but unresolved possibilities. This world's distance and faintness make it a long-term target for future space telescopes capable of atmospheric spectroscopy, but for now it remains a promising candidate whose true nature awaits discovery.
What it would be like
Kepler-991 b is a Neptune-like world — probably wrapped in thick layers of hydrogen, helium, and ices. There may be no solid surface at all, just clouds all the way down.
Surface gravity is about 1.1g — noticeably heavier what you're used to on Earth.
With an equilibrium temperature around -13°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 83 days makes the year 4.4× 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.
Radius2.54R⊕
1/25×Earth = 125×
Mass6.99M⊕
1/10000×Earth = 110000×
Surface gravity1.08g
1/100×Earth = 1100×
Equilibrium temp260 K(-13°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
- 2016
- Facility
- Kepler
- Semi-major axis
- 0.3104 AU
- Period
- 82.53 days
- Eccentricity
- 0.0000
- Density
- 2.34 g/cm³
Detected by measuring the tiny dip in starlight as the planet crosses in front of its star.
Nearly circular orbit.
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
Kepler-991Kepler-991 bOrbitEarth orbitHabitable zone
Drag to rotate · scroll to zoomSemi-major axis: 0.310 AUEccentricity: 0.0000Period: 82.5 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 1,271 light-years?
- A light beam leaving Earth right now would arrive in 1,271 years.
- At Voyager 1's speed (17 km/s), the trip would take approximately 22.4 million years.
- A radio signal sent today would arrive in 1270.6 years — and the reply wouldn't come back for twice that.
Earth Similarity Index
83/1000 — 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.