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Entering orbit…
Habitability
0/ 100
Uninhabitable
51 Peg c rendered in TerraForge from its measured mass, orbit and star

51 Peg c

Also written 51 Pegc

Gas GiantUninhabitable51 light years awayFound 2011
exoplanet.euListed by the Extrasolar Planets Encyclopaedia; not yet in NASA's confirmed catalogue.View on exoplanet.eu

Estimated: this planet doesn't transit its star, so its size is inferred, not measured

51 Peg c, from the Extrasolar Planets Encyclopaedia (found 2011). Measured: 3180 Earth masses, 37 AU, a 5758 K G-type star. Composition inferred from a mass of 3180 Earths, which is giant territory whatever its 1.67x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

51 Peg

Type
G-type (Yellow (Sun-like))
Spectral type
G2IV-V
Temperature
5,758 K
Radius
1.18 ☉
Mass
1.03 ☉
Known planets
2, including this one
Luminosity
1.37 ☉

Published by the Extrasolar Planets Encyclopaedia. This world’s temperature and habitability score are computed from its star’s published radius and temperature.

Gas Giant

Magnetic FieldExtreme Activity
Why is this a Gas Giant?
51 Peg c has 86.0% hydrogen and helium, combined with a mass of 3180.0x Earth, which exceeds the gas giant threshold.
Gas giants form when massive cores capture enormous atmospheres of light gases. They typically form beyond the 'frost line' where volatiles can condense.
Classification Criteria:
✓ Hydrogen + Helium: 86.0% (>60% required)✓ Mass: 3180.0x Earth (>10x required)

Reading 51 Peg c’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while 51 Peg c crosses in front of its star: starlight passes through the atmosphere and spreads into a rainbow band. Each dark line marks a wavelength the atmosphere absorbed.Every element absorbs its own signature wavelengths — hydrogen always darkens the same two spots, calcium another pair, and so on. Astronomers match the lines in a real spectrum against a library of these signatures to say what an atmosphere is made of, light-years away, without ever visiting. A deeper line generally means more of that element is present.51 Peg c sits about 51 light-years away. Most catalogued distances trace back to parallax: as Earth orbits the Sun, a nearby star appears to shift very slightly against the distant background stars, and the size of that shift gives its distance directly.
Further reading
ExoplanetsSara Seager (editor)The field's standard reference: how planets are found, how they form, and what their atmospheres are made of.The Planet FactoryElizabeth TaskerHow planets are made, and why so few of them come out like Earth.Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.
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Habitability ScoreUninhabitable
0
Contributing Factors
temperature0
Near absolute zero - all molecular activity ceases, impossible for life
atmosphere30
Hydrogen-rich atmosphere typical of gas giants
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field100
Magnetic field provides radiation protection
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
3180.00x Earth (1.90e+28 kg)
Radius
14.71x Earth (93,688 km)
This planet: 14.71× Earth radiusEarth: 1× (baseline)
Surface Gravity
14.71x Earth (144.3 m/s²)
Surface Temperature
50 K (-224 °C / -370 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Orbital Environment

Star Type
G-type (Yellow (Sun-like))
Distance from Star
37.00 AU (5.54 billion km)
Orbital Period
225.1 years

Atmosphere

Hydrogen and helium dominated with trace methane and ammonia

Elemental Composition

H - Hydrogen
53.8%
He - Helium
32.3%
O - Oxygen
5.4%

Surface Characteristics

No solid surface - thick gaseous envelope with possible rocky core deep within
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