How to use TerraForge

What this is

TerraForge is a planet builder. You choose the raw ingredients — the chemical elements a world is made of — then pick a star for it to orbit, set how far away it sits, and add moons. Press build, and you watch the planet form out of a cloud of gas and dust.

What you get at the end is not decided by you. It is decided by the physics: your ingredients and your orbit are run through a simulation, and the simulation tells you what they made. Put a lot of iron and rock close to a warm star and you may get something Earth-like. Pile on hydrogen and you get a gas giant. Freeze it out at the edge of the system and you get an ice world.

Every world you save gets its own page and its own link, which you can send to anyone.

Building your first planet

Everything happens in the builder. If you would rather not start from nothing, open the Quick Start Presetsdropdown at the top — it reads “Select a preset...” — and choose something like Earth-like, Mars-like or Gas Giant. That fills in every setting for you, and you can change any of them afterwards.

Otherwise you work through three tabs.

Elements

There are 20 elements to choose from: hydrogen, helium, oxygen, carbon, silicon, iron, magnesium, sulfur, nitrogen, aluminium, calcium, argon, potassium, phosphorus, nickel, sodium, chlorine, titanium, chromium and uranium. You add them as “parts” using the plus and minus buttons — parts are just proportions, so four parts iron to one part oxygen means four times as much iron. Next to each element is an About button that explains what that element is and what it tends to do to a planet.

This mixture is the single biggest decision you make. It is what turns your world into rock, ice, water or gas.

Compounds

Under the elements, on the same tab, are compounds: whole molecules, added in parts just like an element. A part of water (H₂O) puts in two parts hydrogen and one part oxygen — but unlike adding those two elements loose, the world knows they arrived as water. Loose hydrogen and oxygen could end up as almost anything; declared water is water.

They sit in two tabs, and each tab shows how many you have added so nothing goes out of sight.

• Atmosphere — gases that go into the air, thickening it and changing what it is made of: carbon dioxide, the heat-trapping gas Venus is drowning in; methane, which gives ice giants their blue; ammonia; and sulfuric acid, the cloud deck of Venus.
• Surface— oceans, ices and minerals: water, hydrogen peroxide, salt, pyrite (fool's gold), iron-nickel core metal and apatite, the phosphate mineral life runs on. Minerals stay locked in the rock. The oxygen in apatite never becomes air, and salt bleaches the ground into white flats.

You can build with elements alone, compounds alone, or both.

Environment

• Distance from Star, measured in AU. One AU is the distance from the Earth to the Sun. Closer means hotter. The slider stretches to suit the star you pick, so its habitable zone always sits within easy reach. When you are building a planet for one of your star systems, red bands on the track mark the orbits that will not work there — too near one of its other planets, or, around a pair of stars, where their pull would tear an orbit apart — and a warning says why while the handle sits in one.
• Star Type. Ten to pick from: the hot, short-lived O, B, A and F stars; G, which is Sun-like; the cooler K; M, a red dwarf; and three stellar remnants — a black hole, a neutron star and a supernova remnant.
• Initial Mass, in Earth masses, from 0.1 up to about 9,534 — that is 30 times the mass of Jupiter. There is a limit to how big a planet can be: push a hydrogen world past roughly 13 Jupiter masses and it stops being a planet at all. It ignites and becomes a brown dwarf.
• Rotation Speed, the length of one day, anywhere from 1 hour to 2,000 hours. Spin a heavy world fast enough and it flattens out, and the panel tells you its shape. Moons act as a brake on the spin over time, and the Moons tab says how long the day ends up.
• Axial Tilt, from 0° to 180° — how far the planet leans. Under 10° there are almost no seasons; Earth, at about 23°, has ordinary ones; past 40° they turn extreme; near 90° the world rolls around its orbit on its side; and beyond that it spins backwards.

Moons

You can add up to 24. Each moon has a mass and an orbital distance measured in planet radii — so a distance of 5 means five times the planet's own radius out from the centre. The distance matters: bring a moon in too close and the planet's gravity tears it apart into a ring, and put it too far out and it escapes altogether.

Each moon also has a Made ofchoice: leave it on Auto and it forms naturally, or pick silicate rock, iron, water ice, carbon, sulfur, or nitrogen and methane ice. The physics still decides what that becomes. Water ice too close to the star boils off to bare rock; sulfur kept flexed by a neighbour's pull erupts. A tint slider nudges the colour, but only as far as that material could really go. Once the planet is built, you can stand on any moon that survived — see Standing on your planet.

Building it

Press Build Planet, or Ctrl+B. Formation takes about six seconds. You see the gas cloud collapse, material clump together, and a flash as the world is born, while a timeline counts forward from five billion years ago to Present Day. Ctrl+R starts over from a blank slate.

Once it has formed, the panel on the right tells you what you made: Physical Properties, Orbital Environment, Atmosphere, Elemental Composition, Surface Characteristics and Habitability. The build button becomes Edit Planet, so you can go back, change one number, and build again to see what it does.

The buttons on the scene

The view switcher — planet, star system, surface — sits in the top corner of the 3D view. Snapshot, VR and full screen sit in the row along the bottom. On the surface view, look around and sound sit under the habitability score, or on top of the view switcher on a phone. Hovering over any of them shows its name, and some only appear when they apply to your planet or your device.

Standing on your planet

View surface drops you onto the ground. What you find there is read from the same numbers that shaped the globe, so it is your planet, not a stock backdrop.

Depending on what you built, you get bare rock, sand dunes, ice, lava, salt flats, or the cracked plates of a Venus-like world. On a world where the simulation detects life, there is grass and there are trees. On a water world you look out over open ocean. On a gas giant there is no ground at all — there is nothing solid to stand on, so you float among the cloud tops.

The colour of the sky comes from the star you chose. There is weather, there is wind, and there are mountains. And if one of your moons strayed close enough to be torn apart, you will see its debris arcing overhead as a ring. The snapshot button works down there too, so you can take a picture from the ground.

Standing on a moon

The planet is not the only ground. Press View surface on a planet with moons and a small menu asks where to stand: the planet itself, or any moon still in orbit, each tagged with what it became — rock, ice, ocean, 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 cannot see the sun through. And hanging over the horizon is the planet you built.

While you stand on a moon, a tag at the top of the view names it. If more than one moon survived, arrows beside it step between them, and the cross takes you back to the planet in orbit.

Looking around, and VR

On a computer, drag to look around. On a phone or tablet, turn on Look around and the view follows the device instead: hold it up and turn on the spot, and the world turns with you.

Where your browser can do virtual reality, a VR button joins the row along the bottom of the surface view, beside full screen. Tap it, drop your phone into a headset viewer, and you are standing on the ground of a world you made, looking around by turning your head. It works the same on a moon. On Android, Chrome has it; where the button does not appear, your browser cannot do VR.

Saving, sharing, and why an account helps

You can build, save and share a planet without signing in. Name it, save it, and you get a link straight away that anyone can open.

There is one thing worth knowing before you do. A planet saved without an account is always public, and it belongs to nobody — not even you. That means it can never be edited, renamed, deleted or made private later. If you think you might want to change it, make an account first.

An account is free, and it adds:

The AI assistant, and why it needs an account

The star icon in the top-right corner opens an assistant that does two things. Ask it a question about the world you have open — why is there no water on my planet?, how do I make this more habitable?— and it answers from that planet’s own numbers, the same ones used to score it. Or describe a world in plain language and it fills in the elements, orbit, star and spin for you, leaving everything editable.

It never decides what your planet is. It only proposes the numbers; the same simulation that runs everything else works out what those numbers become. If it aims for an ocean world and the physics says otherwise, it tries again — and if the second attempt still misses, it tells you what you actually got rather than pretending.

It is free. There is no paid tier, no credits to buy and nothing to upgrade — an account is simply how we keep one person from using up what everyone else is sharing. Every question costs real money to answer, and asking you to sign in is how it stays free for everybody instead of becoming something we have to charge for. You can see the assistant whether or not you are signed in, so you know what you are making an account for.

Signing in is an email address and a one-time 6-digit code that is sent to it. There is no password to invent and none is ever stored. You need to be 13 or older to make an account. If you are under 13 you can still build planets, save them and share them — you just do it without an account.

Your saved worlds live at My Planets.

Star systems

A star system is a named group of your own planets that all orbit the same kind of star. You make one from My systems New star system, or straight after saving a planet, using “Add to a star system”. You can have up to 20 systems, with up to 20 planets in each.

Two rules govern what fits. First, every planet you add must have been built for that system's star type — a world designed around a red dwarf cannot be dropped into a Sun-like system. Second, the spacing has to work. Real orbital physics checks each new planet against the ones already there. Orbits that would actually cross are refused outright. Orbits that merely sit close enough to go unstable over millions of years give you a warning, and then let you place the planet anyway if that is what you want.

The system's page shows the whole thing as an orrery — a top-down view of the orbits — and tells you whether the arrangement is stable for the long haul. Other people's public systems are at Systems.

Finding your way around

• Explore — every public world on the site. Filter by planet type, by star, or by a minimum habitability, and sort by newest, oldest, top habitability or most liked.
• Planet types — what each kind of planet actually is, with a page for each one. A good place to look if a term in the builder is unfamiliar.
• Systems — public star systems other people have assembled.
• News — real exoplanet headlines, each linking out to the original publication.
• The homepage — shows the Planet of the Week, plus recent worlds from the community.
• The heart on a planet is a like. You need an account to use it.

Keyboard shortcuts

Two, both in the builder. Ctrl+B builds the planet. Ctrl+R starts over.