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
0/ 100
Uninhabitable
HD 128717 b rendered in TerraForge from its measured mass, orbit and star

HD 128717 b

Also written HD 128717b

Brown Dwarf240 light years awayFound 2025
Mass
6290.00 × Earth
Radius
12.10 × Earth
Gravity
42.96 g
Surface (est.)
938 K
Year
9.4 years
From Earth
240 ly
Mass
6290.00 × Earth
Radius
12.10 × Earth
Gravity
42.96 g
Surface (est.)
938 K
Year
9.4 years
From Earth
240 ly

HD 128717 system

Type
F-type (White)
Temperature
6,210 K
Radius
1.25 ☉
Mass
1.21 ☉
Planets
1
Luminosity
2.10 ☉

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.

HD 128717 b4.85 AUYou are here6,290 M⊕
Habitable zone

Star and planets drawn to scale: the star is 11 times as wide as HD 128717 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

HD 128717 b, from the NASA Exoplanet Archive (found 2025). Measured: 6290 Earth masses, 4.85 AU, a 6210 K F-type star. Composition inferred from a mass of 6290 Earths, which is giant territory whatever its 3.55x density suggests, with an assumed 24-hour day — rotation cannot be measured for exoplanets. Note: TerraForge comes out at 938 K against the archive's 152 K, because it models stars by spectral class, and HD 128717 is not an average F-type.

Surface. No surface: a cooling failed star, its methane atmosphere absorbing so much red light it would look magenta to the eye

Brown Dwarf
Magnetic FieldNone Activity
HD 128717 b 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: 6290.0x EarthTemperature: 938K

Reading HD 128717 b’s atmosphere

Dominant elements: H, He, O, C, NThis is what a telescope would measure while HD 128717 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.HD 128717 b sits about 240 light-years away, found by the astrometry 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 ScoreUninhabitable
0
Contributing Factors
temperature1
Scorching - hot enough to melt lead, though rock stays solid; no chance for life
atmosphere30

Hydrogen and helium dominated by methane absorption, with water clouds below

Hydrogen-rich atmosphere typical of gas giants
water15
No solid surface — any water is locked in a supercritical mantle and hot ice, not oceans
magnetic Field20
A strong field, but no surface beneath it — there is nothing here for it to shelter
geology30
Geologically dead - no nutrient recycling
Organic Chemistry80
Core organic elements (CHNO) present
rotation100
Optimal rotation period - balanced day/night cycle, moderate weather, and good heat distribution

Physical Properties

Mass
6290.00x Earth (3.76e+28 kg)
Radius
18.46x Earth (117,605 km)
This planet: 18.46× Earth radiusEarth: 1× (baseline)
Surface Gravity
18.46x Earth (181.1 m/s²)
Surface Temperature
938 K (665 °C / 1,228 °F)
Rotation Period
24.0 hours/day
This planet: 24 h/dayEarth: 24 h/day

Elemental Composition

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