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
79/ 100
Habitable
K2-3 d rendered in TerraForge from its measured mass, orbit and star

K2-3 d

Also written K2-3d, K2 3d, K2 3 d

Water-Rich144 light years awayFound 2015
Mass
2.20 × Earth
Radius
1.46 × Earth
Gravity
1.03 g
Surface (est.)
337 K
Year
44.6 days
From Earth
144 ly
Mass
2.20 × Earth
Radius
1.46 × Earth
Gravity
1.03 g
Surface (est.)
337 K
Year
44.6 days
From Earth
144 ly

K2-3 system

Type
K-type (Orange)
Spectral type
M V
Temperature
3,844 K
Radius
0.546 ☉
Mass
0.549 ☉
Planets
3
Luminosity
0.0587 ☉

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.

K2-3 b0.075 AU5.1 M⊕
K2-3 c0.14 AU2.7 M⊕
K2-3 d0.20 AUYou are here2.2 M⊕
Habitable zone

Star and planets drawn to scale: the star is 41 times as wide as K2-3 d, so only its edge is in view. Orbits spaced as in the star system view.

Water-Rich, likely · its density could also fit a sub-Neptune

K2-3 d is the outermost of three small planets crossing in front of K2-3, a red dwarf about 144 light-years away. It orbits every 44.6 days and is about 1.5 times Earth's width. In 2015 the team that discovered it, led by Ian Crossfield, noted that it sits near the inner edge of the star's habitable zone, the range of distances where liquid water could last on a surface.

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

✓ 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.

Water-Rich
Life possibleMagnetic FieldHigh Activity
K2-3 d has abundant oxygen (30.7%) and hydrogen (26.4%), 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: 30.7% + Hydrogen: 26.4% (water-forming elements)✓ Temperature: 337K (habitable range)✓ Distance: 0.20 AU (habitable zone)

Reading K2-3 d’s atmosphere

Dominant elements: O, H, Si, Fe, N, CThis is what a telescope would measure while K2-3 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.K2-3 d sits about 144 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.
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.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.
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 ScoreHabitable
79
Contributing Factors
temperature46
Warm - livable, but heat stress grows with every degree
atmosphere100

Nitrogen and oxygen with water vapor, mild greenhouse effect

Nitrogen-oxygen atmosphere - breathable and protective
water100
Abundant water
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
2.20x Earth (1.31e+25 kg)
Radius
1.30x Earth (8,286 km)
This planet: 1.30× Earth radiusEarth: 1× (baseline)
Surface Gravity
1.30x Earth (12.8 m/s²)
Surface Temperature
337 K (64 °C / 147 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Elemental Composition

How TerraForge built this world

K2-3 d, from the NASA Exoplanet Archive (found 2015). Measured: 2.2 Earth masses, 0.201 AU, a 3844 K K-type star. Composition inferred from a measured bulk density of 0.71x Earth's at this size, suggesting roughly 36% water/ice by mass, with an assumed 24-hour day — rotation cannot be measured for exoplanets.

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.

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