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Entering orbit…
Habitability
0/ 100
Uninhabitable
HD 77338 b rendered in TerraForge from its measured mass, orbit and star

HD 77338 b

Also written HD 77338b

Ice Giant150 light years awayFound 2012
Mass
15.90 × Earth
Radius
4.12 × Earth
Gravity
0.94 g
Surface (est.)
1,018 K
Year
5.7 days
From Earth
150 ly
Mass
15.90 × Earth
Radius
4.12 × Earth
Gravity
0.94 g
Surface (est.)
1,018 K
Year
5.7 days
From Earth
150 ly

HD 77338 system

Type
G-type (Yellow (Sun-like))
Spectral type
K0 IV
Temperature
5,341 K
Radius
0.97 ☉
Mass
1.37 ☉
Planets
1
Luminosity
0.550 ☉

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.

HD 77338 b0.060 AUYou are here16 M⊕
Habitable zone

Star and planets drawn to scale: the star is 26 times as wide as HD 77338 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

HD 77338 b, from the NASA Exoplanet Archive (found 2012). Measured: 15.9 Earth masses, 0.06 AU, a 5341 K G-type star. Composition inferred from a estimated bulk density of 0.23x Earth's, modeled rather than measured since this isn't a transiting planet, larger than even a pure water/ice world of this mass, suggesting a water-rich interior under roughly a 16% hydrogen/helium envelope by mass, with a day locked to its 5.7-day year, as anything orbiting this close would be.

Surface. No solid surface - a deep volatile envelope over a supercritical water mantle and hot-ice interior

Ice Giant
Magnetic FieldExtreme Activity
HD 77338 b has moderate mass (15.9x Earth) with significant water, carbon, and nitrogen content, characteristic of ice giants.
Ice giants like Uranus and Neptune have icy interiors with thick atmospheres of hydrogen and helium, but not enough to be classified as gas giants.
Classification Criteria:
✓ Mass: 15.9x Earth (5-20x range)✓ Water/Carbon/Nitrogen rich composition

Reading HD 77338 b’s atmosphere

Dominant elements: H, O, Si, He, Fe, NThis is what a telescope would measure while HD 77338 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.HD 77338 b sits about 150 light-years away, found by the radial velocity 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.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.
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 with water, methane, and ammonia ices

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
rotation30
Very slow rotation - days and nights each last several Earth days, bringing extreme temperature swings

Physical Properties

Mass
15.90x Earth (9.50e+25 kg)
Radius
2.51x Earth (16,020 km)
This planet: 2.51× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.51x Earth (24.7 m/s²)
Surface Temperature
1,018 K (744 °C / 1,372 °F)
Rotation Period
137.8 hours/day (slower than Earth)
This planet: 138 h/dayEarth: 24 h/day

Time Dilation

Clocks run 7.8 seconds per year slower than deep space — about 10 minutes over a lifetime

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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