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Entering orbit…
Habitability
48/ 100
Marginal
Ross 128 b rendered in TerraForge from its measured mass, orbit and star

Ross 128 b

Also written Ross 128b

Rocky Terrestrial11 light years awayFound 2017
Mass
1.40 × Earth
Radius
1.11 × Earth
Gravity
1.14 g
Surface (est.)
311 K
Year
9.9 days
From Earth
11 ly
Mass
1.40 × Earth
Radius
1.11 × Earth
Gravity
1.14 g
Surface (est.)
311 K
Year
9.9 days
From Earth
11 ly

Ross 128 system

Type
M-type (Red Dwarf)
Spectral type
M4
Temperature
3,192 K
Radius
0.197 ☉
Mass
0.168 ☉
Planets
1
Luminosity
3.62e-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.

Ross 128 b0.050 AUYou are here1.4 M⊕
Habitable zone

Star and planets drawn to scale: the star is 19 times as wide as Ross 128 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

Ross 128 b is one of the nearest roughly Earth-mass planets known, orbiting a red dwarf about 11 light-years away. A team led by Xavier Bonfils announced it in 2017 after more than a decade of measurements with HARPS, a spectrograph at the European Southern Observatory's La Silla Observatory in Chile. HARPS uses the radial velocity method: as a planet orbits, its gravity makes the star move slightly toward and away from us, and that motion shifts the star's light.

Surface. Rocky surface with impact craters, possible volcanic features

✓ Conditions could support life. This planet’s modelled conditions could support biological processes: stable temperatures, liquid water and the chemistry life as we know it needs. That makes life possible, not present.

Rocky Terrestrial
Life possibleModerate Activity
Ross 128 b is dominated by silicate (25.0%) and iron (12.5%) content, forming a rocky terrestrial body.
Rocky terrestrial planets are primarily composed of silicate rocks and metals. They're the most common type of small planet in the universe.
Classification Criteria:
✓ Silicon: 25.0% + Iron: 12.5% + Magnesium: 3.8%✓ Mass: 1.4x Earth (terrestrial range)

Reading Ross 128 b’s atmosphere

Dominant elements: O, Si, Fe, N, C, HThis is what a telescope would measure while Ross 128 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.Ross 128 b sits about 11 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.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
48
Contributing Factors
temperature99
Warm - livable, but heat stress grows with every degree
atmosphere42

Thin CO₂ and nitrogen atmosphere

Nitrogen atmosphere provides protection but not breathable (partially stripped by slow rotation)
water50
Limited water content
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 - days and nights each last several Earth days, bringing extreme temperature swings

Physical Properties

Mass
1.40x Earth (8.36e+24 kg)
Radius
1.12x Earth (7,127 km)
This planet: 1.12× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.12x Earth (11.0 m/s²)
Surface Temperature
311 K (38 °C / 100 °F)
Rotation Period
236.9 hours/day (slower than Earth)
This planet: 237 h/dayEarth: 24 h/day

Elemental Composition

How TerraForge built this world

Ross 128 b, from the NASA Exoplanet Archive (found 2017). Measured: 1.4 Earth masses, 0.0496 AU, a 3192 K M-type star. Composition inferred from an estimated bulk density of 1.02x 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 9.9-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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