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Entering orbit…
Habitability
58/ 100
Marginal

Reading GJ 273 b’s atmosphere

Dominant elements: O, H, Si, Fe, N, CThis is what a telescope would measure while GJ 273 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.GJ 273 b sits about 19 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.

GJ 273 b

Water-RichMarginal19 light years awayFound 2017

GJ 273 b, from the NASA Exoplanet Archive (found 2017). Measured: 2.89 Earth masses, 0.0911 AU, a 3382 K M-type star. Composition inferred from a estimated bulk density of 0.84x Earth's at this size, modeled rather than measured since this isn't a transiting planet, suggesting roughly 25% water/ice by mass, with a day locked to its 18.6-day year, as anything orbiting this close would be.

Host star

GJ 273

Type
M-type (Red Dwarf)
Spectral type
M3.5
Temperature
3,382 K
Radius
0.293 ☉
Mass
0.29 ☉
Known planets
2, including this one
Luminosity
8.80e-3 ☉

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.

Water World

Life DetectedHigh Activity
Why is this a Water World?Your planet has abundant oxygen (30.8%) and hydrogen (20.5%), creating extensive water coverage while in the habitable temperature zone.
Water worlds have deep global oceans covering most or all of their surface. They form when planets have high water content and orbit in the habitable zone.
Classification Criteria:
✓ Oxygen: 30.8% + Hydrogen: 20.5% (water-forming elements)✓ Temperature: 302K (habitable range)✓ Distance: 0.09 AU (habitable zone)
Further reading
Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.Envisioning ExoplanetsMichael CarrollWhat these worlds might look like from the ground, painted from the same measurements this page renders.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 ScoreMarginal
58
Contributing Factors
temperature100
Optimal temperature range for liquid water and life
atmosphere60
Nitrogen-oxygen atmosphere - breathable and protective (partially stripped by slow rotation)
water100
Abundant water
magnetic Field30
No magnetic field - vulnerable to solar radiation
geology90
Active geology recycles nutrients and drives carbon cycle
Organic Chemistry80
Core organic elements (CHNO) present
rotation30
Very slow rotation - extreme temperature swings between eternal day and night sides

Physical Properties

Mass
2.89x Earth (1.73e+25 kg)
Radius
1.42x Earth (9,075 km)
This planet: 1.42× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.42x Earth (14.0 m/s²)
Surface Temperature
302 K (29 °C / 85 °F)
Rotation Period
446.4 hours/day (slower than Earth)
This planet: 446 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.09 AU (13.6 million km)
Orbital Period
18 days

Atmosphere

Nitrogen and oxygen with water vapor, mild greenhouse effect

Elemental Composition

O - Oxygen
30.8%
H - Hydrogen
20.5%
Si - Silicon
19.4%

Surface Characteristics

Vast oceans covering most of the surface, scattered islands or archipelagos

Habitability

✓ Conditions suitable for life detectedThis planet exhibits the necessary conditions to support biological processes, including stable temperatures, liquid water, and protective magnetic fields.
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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