Create your free account

Enter your email and we'll send a 6-digit code — no password needed.
We only keep your email and the username you choose. We never share or sell your email, and we don't send marketing — we use it only to email you a sign-in code. Read our privacy policy.
Entering orbit…
Habitability
27/ 100
Extremely Harsh

Reading G 9-40 b’s atmosphere

Dominant elements: H, O, Si, Fe, N, CThis is what a telescope would measure while G 9-40 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.G 9-40 b sits about 91 light-years away, found by the transit 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.

G 9-40 b

BarrenExtremely Harsh91 light years awayFound 2019

G 9-40 b, from the NASA Exoplanet Archive (found 2019). Measured: 4 Earth masses, 0.0418 AU, a 3395 K M-type star. Composition inferred from a measured bulk density of 0.58x Earth's at this size, suggesting roughly 64% water/ice by mass, with a day locked to its 5.8-day year, as anything orbiting this close would be.

Host star

G 9-40

Type
M-type (Red Dwarf)
Spectral type
M2.5 V
Temperature
3,395 K
Radius
0.303 ☉
Mass
0.295 ☉
Known planets
1 (this one)
Luminosity
0.0110 ☉

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 waterHigh 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: 4.0x EarthTemperature: 484K
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 ScoreExtremely Harsh
27
Contributing Factors
temperature15
Extremely hot - hostile to known life forms
atmosphere70
Nitrogen atmosphere provides protection but not breathable
water59
Abundant water - likely as steam
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
4.00x Earth (2.39e+25 kg)
Radius
1.59x Earth (10,113 km)
This planet: 1.59× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.59x Earth (15.6 m/s²)
Surface Temperature
484 K (211 °C / 411 °F)
Rotation Period
138.0 hours/day (slower than Earth)
This planet: 138 h/dayEarth: 24 h/day

Orbital Environment

Star Type
M-type (Red Dwarf)
Distance from Star
0.04 AU (6.25 million km)
Orbital Period
6 days

Atmosphere

Thin CO₂ and nitrogen atmosphere

Elemental Composition

H - Hydrogen
40.0%
O - Oxygen
30.4%
Si - Silicon
11.9%

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.

Create your free account

Enter your email and we'll send a 6-digit code — no password needed.
We only keep your email and the username you choose. We never share or sell your email, and we don't send marketing — we use it only to email you a sign-in code. Read our privacy policy.

Send feedback

We're still building out the best experience we can — and we'd love your input. Tell us about features you enjoy, ideas you'd like to see, or pain points where something feels off, and we'll know where to look next.

Type
Idea
Bug
Pain point
Other