Manual

The app opens on today's date with the Sun, the eight planets, Pluto and the Moon roughly where they really are, already moving. Time runs at 30 days per second.

• The Orbliterator panel (top left, "Controls" on a phone) holds time, speed and what you see.
• Obliterate (top right) holds the scenarios, the list of events and everything for launching.
• Click a planet and its info panel opens, with the buttons to follow it, centre on it, delete it or tamper with it.

Every panel folds to its title with the arrow in its head, and so does each block inside it (View, Scenarios, Events, Launch settings, Tamper). The browser remembers which ones you left open.

On a phone the panels are tucked away behind a bar at the bottom of the screen. See On a phone or tablet.

Moon labels only appear once you zoom in far enough.

• Pause (Space) stops and starts the clock. The date shows under the title.
• Speed goes from 0.1 days to about 2.7 years per second.
• Backwards (R) runs time the other way. The planets retrace their paths very closely; only bodies that merged stay merged.
• Reset brings back today's solar system and clears everything you did.
• Share makes a link to the system as it is now; see Sharing.

The line at the bottom of that panel counts the bodies and says when time is paused or running backwards. "Can't keep up" means the computer cannot calculate as fast as the speed asks; the picture stays smooth, time just runs slower than set. That mostly happens with the moons switched on.

• Centre draws everything as seen from one body. "Barycentre", the default, is the balance point of the whole system, close to the Sun. Pick Earth and the Sun circles you once a year while Mars and Venus trace loops. Only the picture changes, not the physics.
• Planet size sets how much bigger than real the bodies are drawn. The default is 11.
• Labels and Trails switch the names and the lines behind the bodies on and off. A trail shows the last orbit and fades out at its oldest end.
• Moons adds the fifteen big moons of Jupiter, Saturn, Uranus, Neptune and Pluto. They are real bodies in the simulation, so it gets a lot slower.
• Pluto counts as a planet removes Pluto (and Charon) or puts it back where it would be now.
• Original orbits shows, as a dashed line with a see-through ghost, where a body would have been without your launches and changes. A ghost only appears once a body is visibly off course.

The info panel shows the type, mass, radius, speed and distance of the selected body. Speed and distance are measured from what it goes round: a planet from the Sun, the Moon from Earth.

• Follow keeps the camera on the body.
• Center (C) makes it the centre of the picture; press again to go back to the barycentre.
• Delete (Delete) removes it. Its moons stay, and now have nothing to hold on to.

Open Tamper in the info panel to change a body that is already there.

• Name: rename it.
• Mass: pick a preset, drag the slider or use ×0.1, ×10 and Original. Make a planet heavy enough and it becomes a gas giant or a star, and back again when you lower it.
• Speed and direction: type them, or use ×0.5, ×1.5, Reverse and Stop. They are relative to what the body goes round. Its moons come along with any change.

Directions work the same everywhere in the app: 0° is along with the orbit, 90° straight outward, 180° against the orbit, 270° straight inward.

Open Launch settings in the Obliterate panel and press Launch mode (L). Then:

• Click on the plane of the orbits to put a body there in a round orbit around whatever is nearest and heaviest, usually the Sun, or a planet when you click close to it.
• Drag to aim: the arrow sets the direction, its length the speed. The dotted line shows where it will go in the next thousand days. Let go to launch.

Before you launch:

• Name: leave it empty and the body gets a silly name that fits its size.
• Mass preset and Mass: from an asteroid via the Moon, Earth, Jupiter, a red dwarf and the Sun up to a black hole of ten solar masses.
• Click without dragging: round orbit: untick it and a plain click uses the speed and direction typed below instead.

Bodies that touch merge into one. Mass and momentum add up, so a planet that swallows enough becomes a gas giant or a star. A black hole does not wait for a touch: its tides tear apart anything that comes within about a million km. Press L or Esc to leave launch mode.

In launch mode you can also grab an existing planet or moon and drag it somewhere else. Time stands still while you hold it. It keeps its speed and direction, and its moons come along.

When you let go, a window opens with its mass, speed and direction, the dotted path ahead, and a line saying whether it will escape or how long an orbit takes. Use round orbit gives it exactly the speed for a round orbit at that spot. Done starts time again.

A moon dragged too far from its planet gets pulled away by the Sun, even in a round orbit. The window warns you when that happens.

Open Scenarios at the top of the Obliterate panel, pick one, read what it does and press Play scenario. Each one starts from today's solar system, adds one disaster or oddity, and sets a fitting speed, camera and planet size.

Disasters

• A star flies by
• A black hole passes through
• Jupiter ignites
• A second Sun
• The Sun loses half its mass
• Earth stops
• The Moon breaks free

Strange but stable

• The Sun is a binary star
• Bonkers, but stable
• Jupiter and Saturn dance
• A crown of Jupiters
• Every which way
• Inside out
• Three suns in a figure eight
• Four, eight, sixteen and thirty-two suns

Two options change how a scenario starts:

• Keep my view keeps your camera, centre and the body you follow.
• Keep my solar system adds the disaster to the system as it is now, with everything you launched, changed or wrecked. If the scenario needs a body that is gone (Earth stops, without Earth), it says so and does nothing.

When a body is flung out of the solar system or destroyed in a collision, a message pops up with a Replay button, and the event goes into the Events list in the Obliterate panel.

• Replay, or clicking an event in the list, plays it again in slow motion: from a few seconds before until a few seconds after, then time runs at its old speed. Changing the speed yourself ends the slow motion.
• Back to where you were returns you to the moment you left.
• Clear list empties the list. Reset and a new scenario do that too.

Events are only noticed while time runs forwards. A moon that leaves together with its planet is not counted separately, and a visitor from outside, like a passing star, cannot be ejected.

Share, next to Reset, makes a link to your solar system exactly as it is now. On a computer the link is copied, ready to paste; on a phone your share menu opens.

Whoever opens the link gets:

• every body where it is at that moment, with its speed, mass and name, including everything you launched, changed or merged
• the date, the speed, and whether time was paused or running backwards
• your view: camera, centre, the body you follow or selected, planet size and the switches in the View block

From there it runs exactly as it would have on your screen. Not included: the Events list, the dashed original orbits (they start again from the shared moment) and your launch settings.

The system travels inside the link itself: nothing is stored on a server. Reset still brings back today's solar system.

On a phone the screen belongs to the solar system. All you see at first are the planets and a bar at the bottom. The panels hide behind that bar and open one at a time above it.

The bottom bar

An open panel takes up at most about half the screen; scroll inside it when there is more. Tap the title of a block (View, Scenarios, Launch settings) to open or close it.

Looking around

To follow a body, select it and tap Follow.

The info panel

On a phone the info panel of the selected body sits at the top of the screen, out of the way of the bar. Opening Tamper closes any open panel and stretches the info panel, so all its controls fit. Tap the arrow in its head to fold it to just the name, and again to open it.

Launching

1. Tap Launch, open Launch settings and pick a name and a mass.
2. Tap Aim. The panel closes.
3. Tap a spot for a round orbit, or drag with one finger to aim: the arrow and the dotted path follow your finger. Lift it to launch.
4. Changed your mind? Put a second finger down. The aim is dropped and you zoom or pan instead.
5. Tap Aim again to stop launching.

A drag counts for more on a small screen, so you don't need a long one: about 2 cm already gives Earth's speed of 30 km/s.

With Aim on, put your finger on a planet or moon to drag it somewhere else. The window for its mass, speed and direction opens when you let go.

Good to know

• Messages, such as a launch or an event with its Replay button, appear just above the bar.
• There are no keys on a phone, but every key has a button: Delete is in the info panel, Backwards under Controls.
• Phones get a lighter Milky Way and a slightly softer picture, to spare memory.
• The Moons switch makes the simulation much heavier. On a phone time may run slower than the Speed slider says.
• A tablet, or a large phone held sideways, often gets the desktop layout: panels in the corners with fold arrows, no bottom bar. The finger gestures stay the same; for launching use the Launch mode button in Launch settings.

Keys do nothing while you are typing in a field or the window after moving a body is open.

See Mars go backwards. Set Centre to Earth and the speed to about 30 days per second. Every two years Mars stops, loops back and carries on.

Drop a black hole. Pick the Black hole preset, press L and drag from outside Neptune's orbit towards the Sun. Switch on Original orbits to see where everything should have been.

Give Earth a second moon. Pick the Moon preset, zoom in on Earth, press L and click next to it. A plain click puts it in a round orbit around Earth.

Turn Jupiter into a star. Select Jupiter, open Tamper and press ×10 twice. Watch what the rocky planets do.

Watch an ejection again. Play "The Sun loses half its mass", wait for the first message and press Replay.