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

HN Peg b

Also written HN Pegb

Brown Dwarf59 light years awayFound 2006
Mass
6990.00 × Earth
Radius
11.80 × Earth
Gravity
50.20 g
Surface (est.)
1,185 K
Year (est.)
18,849 years
From Earth
59 ly
Mass
6990.00 × Earth
Radius
11.80 × Earth
Gravity
50.20 g
Surface (est.)
1,185 K
Year (est.)
18,849 years
From Earth
59 ly

HN Peg system

Type
F-type (White)
Spectral type
G0 V
Temperature
6,186 K
Radius
1.01 ☉
Mass
1.08 ☉
Planets
1
Luminosity
1.15 ☉

Published by the NASA Exoplanet Archive. This world’s temperature and habitability score are computed from this star’s measured luminosity, not from a stand-in for its class.

HN Peg b773.00 AUYou are here6,990 M⊕
Habitable zone

Star and planets drawn to scale: the star is 9.3 times as wide as HN Peg b, so only its edge is in view. Orbits spaced as in the star system view.

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

HN Peg b, from the NASA Exoplanet Archive (found 2006). Measured: 6990 Earth masses, 773 AU, a 6186 K F-type star. Composition inferred from a mass of 6990 Earths, which is giant territory whatever its 4.25x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets. Note: TerraForge comes out at 1185 K against the archive's 11 K, because that figure is the planet's own heat, not the star's. It receives almost no sunlight out at this distance and is still glowing from its formation — TerraForge only warms worlds with starlight, so it has no way to model a planet heated from within.

Surface. No surface: a cooling failed star, its methane atmosphere absorbing so much red light it would look magenta to the eye

Brown Dwarf
Magnetic FieldNone Activity
HN Peg b has an unusual composition that doesn't fit standard classifications, or lacks the elements needed for complex geological processes.
Barren worlds can form from uncommon element combinations or may be remnants of larger bodies that lost their atmospheres and volatile materials.
Classification Criteria:
Composition doesn't match standard planet typesMass: 6990.0x EarthTemperature: 1185K

Reading HN Peg b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while HN Peg b 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.HN Peg b sits about 59 light-years away, found by the imaging method. 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.The Little Book of ExoplanetsJoshua WinnHow these worlds are found, and what a measurement can honestly tell us.Exoplanets: Diamond Worlds, Super Earths, Pulsar PlanetsMichael Summers & James TrefilThe strange end of the catalogue — carbon worlds, molten rock, planets orbiting dead stars.
As an Amazon Associate I earn from qualifying purchases — if you buy through these links, TerraForge may receive a small commission at no extra cost to you.
Habitability ScoreUninhabitable
0
Contributing Factors
temperature0
Inferno world - temperatures exceed all possibility of life
atmosphere30

Hydrogen and helium dominated by methane absorption, with water clouds below

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 Field20
A strong field, but no surface beneath it — there is nothing here for it to shelter
geology30
Geologically dead - no nutrient recycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
6990.00x Earth (4.17e+28 kg)
Radius
19.12x Earth (121,815 km)
This planet: 19.12× Earth radiusEarth: 1× (baseline)
Surface Gravity
19.12x Earth (187.6 m/s²)
Surface Temperature
1,185 K (912 °C / 1,673 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Elemental Composition

A dark ringed planet hanging over the horizon of a rocky moon, its rings lit by a distant sun

New: Stand on Your Moons 🌒

A planet's surface view isn't the only ground any more. Press the surface button on a planet with moons and it asks where to stand: the planet itself, or any moon still in orbit, each tagged with what it became — ocean, ice, carbon, volcanic. Every moon gets its own ground and sky from its own physics: airless rock under a black sky, ice cracked by geysers over a hidden sea, sulfur plains shaking with eruptions, or orange haze you can't see the sun through. And hanging over the horizon, there's the planet you built.

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