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Entering orbit…
Habitability
42/ 100
Marginal

Reading HD 20794 d’s atmosphere

Dominant elements: H, O, Si, Fe, N, CThis is what a telescope would measure while HD 20794 d 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 20794 d sits about 20 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.

HD 20794 d

BarrenMarginal20 light years awayFound 2011

HD 20794 d, from the NASA Exoplanet Archive (found 2011). Measured: 4.8 Earth masses, 0.362 AU, a 5368 K G-type star. Composition inferred from a estimated bulk density of 0.57x Earth's at this size, modeled rather than measured since this isn't a transiting planet, suggesting roughly 71% water/ice by mass, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

Host star

HD 20794

Type
G-type (Yellow (Sun-like))
Spectral type
G6 V
Temperature
5,368 K
Radius
0.93 ☉
Mass
0.79 ☉
Known planets
4, including this one
Luminosity
0.687 ☉

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.

Barren

No life — too hot for liquid waterMagnetic FieldHigh Activity
Why is this a Barren?Your planet 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: 4.8x EarthTemperature: 458K
Further reading
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.Envisioning ExoplanetsMichael CarrollWhat these worlds might look like from the ground, painted from the same measurements this page renders.Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.
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 ScoreMarginal
42
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere70
Nitrogen atmosphere provides protection but not breathable
water68
Abundant water - likely as steam
magnetic Field100
Magnetic field provides radiation protection
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
4.80x Earth (2.87e+25 kg)
Radius
1.69x Earth (10,747 km)
This planet: 1.69× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.69x Earth (16.5 m/s²)
Surface Temperature
458 K (185 °C / 364 °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
0.36 AU (54.2 million km)
Orbital Period
80 days

Atmosphere

Thin CO₂ and nitrogen atmosphere

Elemental Composition

H - Hydrogen
42.8%
O - Oxygen
30.3%
Si - Silicon
10.7%

Surface Characteristics

Barren rocky surface with unusual elemental composition
A binary star system's orrery: two suns close together, a red dashed dead-zone boundary, and a debris trail left by a destroyed world

New: Binary Star Systems 🌀

A system can now orbit two suns. Add a companion star when you build one — close, medium, or wide — and the physics decides what survives: a shared center of mass carves out a dead zone where gravity from both stars tears a world apart, leaving it as debris, and every surviving planet's orbit goes elliptical, moving fastest at closest approach and slowest out at aphelion. Push the separation to wide and the dead zone opens tens of AU across, wide enough to gut a system that would have been stable around one star alone. Stand on a world that made it through and you'll watch two suns cross the sky together.

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