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Entering orbit…
Habitability
0/ 100
Uninhabitable
55 Cnc e rendered in TerraForge from its measured mass, orbit and star

55 Cnc e

Also written 55 Cnce

Lava World41 light years awayFound 2004
Mass
7.99 × Earth
Radius
1.88 × Earth
Gravity
2.26 g
Surface (est.)
2,000 K
Year
17.7 hrs
From Earth
41.1 ly
Mass
7.99 × Earth
Radius
1.88 × Earth
Gravity
2.26 g
Surface (est.)
2,000 K
Year
17.7 hrs
From Earth
41.1 ly

55 Cnc system

Type
K-type (Orange)
Spectral type
G8 V
Temperature
5,172 K
Radius
0.943 ☉
Mass
0.905 ☉
Planets
5
Luminosity
0.635 ☉

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.

55 Cnc e0.015 AUYou are here8.0 M⊕
55 Cnc b0.12 AU264 M⊕
55 Cnc c0.25 AU55 M⊕
55 Cnc f0.80 AU45 M⊕
55 Cnc d5.60 AU1,230 M⊕
Habitable zone

Star and planets drawn to scale: the star is 55 times as wide as 55 Cnc e, 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

NASA calls the evidence for gas around 55 Cancri e the best yet for an atmosphere on a rocky planet beyond our Solar System. The planet, also named Janssen, was first detected in 2004 with the Hobby-Eberly Telescope at McDonald Observatory. That team used the radial velocity method, which measures the tiny wobble a planet's gravity causes in its star. They put its orbit at 2.8 days. In 2011, after other astronomers predicted a much shorter orbit, the MOST space telescope caught the planet passing in front of its star every 0.74 days, about 18 hours. The star is bright enough to see with the naked eye, which makes the planet unusually easy to study.

Surface. Molten surface with lava flows, volcanic activity everywhere

Lava World
Magnetic FieldExtreme Activity
55 Cnc e's proximity to its star (0.02 AU) results in extreme surface temperatures of 2000K.
Lava worlds orbit so close to their stars that rocky surfaces melt into oceans of molten rock. Recent planet formation can also create temporary lava worlds.
Classification Criteria:
✓ Temperature: 2000K (>1000K)

Reading 55 Cnc e’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while 55 Cnc e 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.55 Cnc e sits about 41 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.Imagined LifeJames Trefil & Michael SummersWhat could live on a world like this one: ice shells, supergravity, tidally locked twilight.
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Habitability ScoreUninhabitable
0
Contributing Factors
temperature0
Inferno world - temperatures exceed all possibility of life
atmosphere10

Minimal - too hot to retain

No atmosphere - exposed to radiation and temperature extremes
water8
Limited water content - boiling away, little would be retained
magnetic Field100
Magnetic field provides radiation protection
geology40
Extreme volcanic activity may be hazardous
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
7.99x Earth (4.77e+25 kg)
Radius
2.00x Earth (12,737 km)
This planet: 2.00× Earth radiusEarth: 1× (baseline)
Surface Gravity
2.00x Earth (19.6 m/s²)
Surface Temperature
2,000 K (1,727 °C / 3,140 °F)
Rotation Period
17.7 hours/day (faster than Earth)
This planet: 18 h/dayEarth: 24 h/day

Time Dilation

Clocks run 21.2 seconds per year slower than deep space — about 28 minutes over a lifetime

Elemental Composition

How TerraForge built this world

55 Cnc e, from the NASA Exoplanet Archive (found 2004). Measured: 7.99 Earth masses, 0.0154 AU, a 5172 K K-type star. Composition inferred from an estimated bulk density of 1.20x Earth's, modeled rather than measured since this isn't a transiting planet — the radius is the archive's estimate, so it can't settle how much water there is; read as rock and iron, with a day locked to its 0.7-day year, as anything orbiting this close would be.

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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