Solaris

Sol is the Latin name for our Sun. Solaris shows its family in two ways: as it stands today, or on any date from 3000 BC to AD 3000, and as it might have formed, starting from a spinning cloud of dust.

Our Solar System

The opening view is the real Solar System at this moment: the Sun, the eight planets, six dwarf planets, four large or famous asteroids, seven comets including the interstellar visitor 3I/ATLAS, sixteen moons, Saturn's rings and three spacecraft heading out of the Solar System. Set any date and time, run the clock forward or backward from real time up to a century per second, and click anything to see how far it is from the Sun and from Earth, how fast it is moving, and when it next swings closest to the Sun.

The planets come from the formulas NASA's Jet Propulsion Laboratory publishes for approximate planet positions, by E. M. Standish and J. G. Williams. Each planet's orbit is described by six numbers that change slowly over the centuries; Kepler's equation turns them into a position. Between 1800 and 2050 they are good to about a minute of arc for the inner planets and ten minutes for Saturn, and they stay usable over the whole span from 3000 BC to AD 3000.

Dwarf planets, asteroids and comets are moved along fixed orbits from published elements, mostly from the JPL Small-Body Database. That ignores the tugs of the planets, so their positions are best near today and drift as you move decades away; each details card says where its numbers come from. Earth's Moon uses a simple lunar theory good to about a degree. The other moons have their real distances, periods and orbit planes, but their positions around their planets are illustrative. The spacecraft are placed along straight lines in their current directions, so they appear only after their last planet flybys.

The dust of the asteroid belt and Kuiper belt is not a catalog of real objects. It is a statistically realistic crowd generated to match the real populations, moved on the graphics card for whatever date you choose:

Main belt, between Mars and Jupiter, with the Kirkwood gaps where Jupiter's resonances have cleared out orbits.
Hildas, which go around the Sun three times for every two of Jupiter's, and so cluster in a triangle with Jupiter at one corner.
Trojans, sharing Jupiter's orbit in two swarms 60° ahead of it and 60° behind.
Near-Earth asteroids, whose orbits reach inside 1.3 AU.
The Kuiper belt, beyond Neptune, with a thin "cold" disk and a puffed-up "hot" population.
Plutinos, like Pluto, which circle the Sun twice for every three of Neptune's laps and so never meet it.
The scattered disk, stretched orbits flung outward long ago by Neptune.

The planets are drawn as dots a few pixels across so you can find them; their real sizes would be invisible at this scale. Switch to True scale under View to see how empty space really is. Rings and moons appear as you zoom in close enough to separate them from their planets.

Beyond the planets

Keep zooming out, or use the Zoom through space buttons, and Solaris goes on past the planets. At about 120 AU a faint sphere marks the heliopause, where the solar wind gives way to the gas between the stars; both Voyagers have crossed it. Far beyond lies the Oort cloud, a vast shell of icy bodies that stretches from a few thousand AU to perhaps 100,000 AU, a good part of the way to the nearest star. It is the source of long-period comets, but no Oort cloud object has ever been seen there directly, so its dots are an illustration.

Then come the stars. Thirty-six real stars sit at their measured directions and distances: every star within about 13 light-years, plus famous ones such as Vega, Arcturus, Polaris, Betelgeuse, Rigel and Deneb, and the Pleiades cluster. Click one to see how far away it is and the year the light you see from it left. Their positions come from star catalogs; the stars' own slow drift across the sky over the centuries isn't shown.

Zoom out further and the Sun becomes one point in the Milky Way, 26,700 light-years from the center. The galaxy is a model, not a map: a central bar, four spiral arms wound at 12°, the Orion Spur the Sun sits in, and a thinner disk, oriented correctly in the sky so that from inside it appears as the Milky Way's band. Real maps of our galaxy are still uncertain, because we see it from inside, through its dust.

11,800 real stars

Every star you can see with the naked eye, about 8,700 of them down to magnitude 6.5, plus the 3,600 nearest stars (everything within about 90 light-years), sits at its measured position and distance from the HYG database, which combines the Hipparcos, Yale Bright Star and Gliese catalogs. Each star's brightness is worked out from where your camera is, so from the Sun you see the real night sky, and as you fly outward the constellations come apart: their stars only look close together from here. Stars whose distances are still poorly measured may sit too close or too far. The stars' own slow drift across the sky over the centuries isn't shown.

The sky from where you stand

Under Sky from a place on Earth, press Use my location, or type a latitude and longitude, and Solaris puts you on Earth's surface at that spot, looking at the sky for the date and time set above. Daylight washes out the stars when the Sun is up, twilight glows along the horizon after sunset, and the ground hides whatever is below the horizon. Drag to look around, zoom in to see the Moon's phase or Saturn's rings, and search for any planet, star, galaxy or constellation to turn toward it. Press Leave the ground, or Escape, to return to space.

On a phone or tablet, Aim with my phone turns it into a window on the sky: Solaris reads its location and the direction it's pointing from its compass, accelerometer and gyroscope, so you can hold it up to a star or planet and see its name. Phone compasses are easily thrown off by metal and electronics nearby, and some point to magnetic rather than true north, so if the view is turned slightly, choose the Moon, the Sun or a bright planet, point the phone right at it and press Calibrate.

A compass rose in the corner shows which way you're facing. Double-tap it to line the sky up by hand: drag until the overlay sits on the real Moon or a bright star, or nudge heading and height with the − and + buttons, then double-tap the compass again to keep the correction. Show the camera puts your phone's live camera picture underneath the sky, so you can line things up against the real view; pinch or use the zoom bar to zoom in on distant objects. If stars drift apart toward the edges of the picture, adjust Camera view in the lining-up panel to match your camera's field of view.

The Sun up close

Zoom in on the Sun and it shows its corona, the faint outer atmosphere seen during total eclipses, streaming into space in long rays; pink prominences arching off its edge; and, every so often, a coronal mass ejection, a billion-ton cloud of solar plasma blasting outward. These are drawn to resemble what coronagraphs on spacecraft such as SOHO record, but they are not today's actual solar activity, and they are shown hundreds of times faster than life: a real ejection takes about a day to cross the distance shown.

Satellites and spacecraft journeys

Two extra sets of data load only when you ask, under Extra data. Load Earth satellites downloads the current orbits of about 10,000 working satellites from CelesTrak and places each one with SGP4, the standard model used to track them. Zoom in close to Earth to see the swarm: the dense cloud in low orbit, the navigation satellites farther out, and the ring of geostationary satellites about a tenth of the way to the Moon. From the ground you can watch them pass overhead. Search any satellite by name (ISS, Hubble, Starlink, GPS) or catalog number, or tap one, to see its height, speed, type of orbit and how fresh its orbit data is, with its orbit drawn around Earth. Standing on the ground, its card also gives the next time it passes over you, whether it should be visible, and a button to watch that pass. Positions are good to a few kilometers when the data is fresh and drift by roughly a few kilometers a day for low satellites, so they're best within a few days of loading.

On the ground, whenever something is selected, a gold circle marks it and arrows show which way to turn and tilt to find it; the crosshair in the middle turns green when you're on it. With Aim with my phone on, just follow the arrows with the phone; on phones that allow it, it ticks faster as you get within 15° and gives a double buzz when you're on target. Phones have a single vibration motor, so left and right can't be felt directly; switch Vibration style to Direction code to have the rhythm tell you which way to turn (one long buzz: right; two short: left; short then long: up; long then short: down), or turn on the Sound guide and wear earbuds: the ticks come from the side to turn toward, and also sound different: one clean tick for right, a double tick-tick for left, so you can tell without earbuds. Higher pitch means tilt up and lower means tilt down. Find in sky on any object's card does all of this in one tap: it stands you where you are, turns on the phone's sensors and starts guiding you to it.

Loading satellites also fetches the spacecraft working at other worlds, from JPL's Horizons system: the Lunar Reconnaissance Orbiter, Chandrayaan-2 and Danuri at the Moon; Mars Reconnaissance Orbiter, MAVEN, Mars Odyssey, Mars Express, the Trace Gas Orbiter and Hope at Mars; and the James Webb and Euclid telescopes at the Sun–Earth L2 point, with SOHO and DSCOVR at L1. Each is fetched for a few days around the date shown and refreshed as the date moves, so its orbit is accurate; zoom in on the Moon or Mars to see them circling, with their paths drawn. Spacecraft that have ended their missions, or whose data isn't available for the date, are simply left out.

Load spacecraft journeys downloads the actual paths of 14 deep-space missions from NASA JPL's Horizons system. Choose one, such as Voyager 2 or Cassini, and press Replay journey: the clock goes back to its launch and the camera follows it as it swings past the planets that slung it onward.

Into the very small

Keep zooming into the Sun, or press Into the Sun's surface or Into the Sun's core under Zoom through space, and Solaris carries on into the very small: about sixty powers of ten from the edge of the observable universe down to the Planck length. The surface dive passes through the granulation cells to the thin glowing gas, then to individual hydrogen and helium atoms (there are no intact atoms in the core: it's too hot), into a helium atom's electron cloud, down to its nucleus of two protons and two neutrons, into a proton and its three quarks, and on to the Planck length. The core dive goes down through the Sun's layers to the plasma of bare nuclei and electrons, where you can watch protons fuse. Use Dive and Rise, or zoom by hand.

Below the size of an atom nothing can be photographed, even in principle, so these scenes use the standard scientific pictures: electron clouds showing where electrons are likely to be, with sparks drawn from the true probability distribution; quarks in the three "colors" that stand for color charge; gluon strings between them. Sizes, spacings, temperatures and speeds are real; the fusion flashes are sped up enormously; and the quantum foam at the bottom is an artist's idea of something no one has observed.

Tonight's sky tour

Choose what you're observing with (your eyes, binoculars or a small telescope) and how dark your sky is, and Start tonight's tour picks from about 120 hand-chosen sights the ones you have a real chance of seeing from where you are, right now: the planets and Moon, showpiece stars and double stars, star clusters, nebulae and galaxies. Each must be high enough above the horizon, the sky dark enough, and faint objects aren't suggested when a bright Moon would wash them out. Objects about to set come first; the rest follow a path across the sky from one to its nearest neighbor, easiest first. The finder guides you to each one; tap I saw it to log it, Read to hear what to look for and why it's interesting, and Info for its details. Your log stays on this device only, and you can export it as a spreadsheet. How faint you can see depends a lot on your eyes, the air and how long you've let them adjust to the dark, so treat "challenging" as a real challenge.

Constellations

Turn on Constellations under Show to draw the 88 constellations the International Astronomical Union recognizes, as stick figures joining their real stars, with their names. Search for one by name, Latin or English (Orion, Ursa Major, Great Bear, Scorpius), and choose View from Earth to fly to Earth and look at it. Then zoom out. The lines join the stars where they really are in space, so the familiar shapes only hold together as seen from near the Sun. Fly a few dozen light-years away and they twist; fly farther and they collapse into a tangle, because stars that look side by side in our sky can be hundreds of light-years apart.

1,000 nearby galaxies

Beyond the Milky Way are the 1,000 nearest known galaxies, out to about 31 million light-years, from the Catalog & Atlas of Local Volume galaxies by Igor Karachentsev and colleagues. Each sits at its measured direction and distance at its real size. Their distances are uncertain by roughly 5 to 15%, so the 3D arrangement is approximate in depth. They are drawn, not photographed: spirals, ellipticals, lenticular, irregular and dwarf galaxies each get a shape from their catalogued type and are tilted to match how flattened they look from Earth. The catalog doesn't record which way each galaxy's long axis points, so that is chosen at random. Most of the thousand are faint dwarfs with catalog names; the famous ones, such as Andromeda, Triangulum, the Magellanic Clouds, Centaurus A, the Whirlpool and the Sombrero, are labeled from farther away.

Real images of the planets

Zoom in until a planet or moon is bigger than its marker dot and it becomes a sunlit globe wrapped in real imagery, turning at its true rate and tilted on its true axis. Day and night fall where they really are for the date and time shown, so the Moon shows its real phase, and the Sun rises over the right part of the Earth.

Earth is drawn from NASA's Blue Marble, with city lights from NASA's Black Marble on its night side. Its clouds are real: for the date being shown, Solaris loads that day's global true-color mosaics from two NASA weather satellites (VIIRS on Suomi NPP and NOAA-20, through NASA's GIBS service) and lifts the clouds out of them. Each part of the mosaic was photographed at about 1:30 pm local time, so the clouds are that day's, not this minute's; today's mosaic is still filling in, so the latest shown is yesterday's. Before late 2015, when the satellite record starts, Earth is shown clear.

The other planets and the Moon use maps from Solar System Scope, built from NASA mission data. Zoom in closer still and the Sun, Mercury, Venus, Earth, Moon, Mars, Jupiter and Saturn switch to 8K maps (8,192 pixels around), stored in a compressed format the graphics chip reads directly, so each takes only about 20 MB of graphics memory; they're released again when you move away. Venus is shown under a veil of cloud over its radar-mapped surface, and Saturn's rings are drawn from their measured bands, with the planet's shadow falling across them.

To the edge of the observable universe

Beyond the 1,000 nearest galaxies, which reach only about 31 million light-years and are drawn with their shapes, Solaris shows 43,000 more as small points from the 2MASS Redshift Survey, an all-sky map of the brightest galaxies in infrared light out to about two billion light-years. Fly out with Cosmic web and the galaxies stop looking scattered: they line up in walls and filaments around vast empty voids, with great clusters such as Virgo, Coma, Perseus and the Shapley Supercluster at the knots. Labels mark those clusters, two famous quasars, and the most distant galaxies known: GN-z11, JADES-GS-z14-0 and the current record holder, MoM-z14, seen as it was only 280 million years after the Big Bang. Farthest of all is the cosmic microwave background, the oldest light there is, from 380,000 years after the Big Bang. Zoom out past it and it appears as a sphere wrapped in a real map of that light, laid out in its true direction on the sky: red patches were slightly warmer and blue slightly cooler, by about a ten-thousandth of a degree, the seeds from which the cosmic web grew. From inside, it shows faintly behind everything else. Nothing beyond it can be seen; it is the edge of the observable universe, about 45 billion light-years away.

Hundreds of millions of galaxies have been catalogued, far too many for a web page, so the deep universe here is a sample: complete for the brightest galaxies nearby, then just the landmarks. Because space has been expanding while their light traveled, distances this far out are given as they are now, which is larger than the light's travel time in years. Distances use the standard Planck 2018 cosmology. The galaxy points are colored by distance, from blue-white for the nearer ones to orange for the farthest. Seen all at once, the map is a ball of points; to see its structure, orbit around it, or turn on the thin slice, which keeps only galaxies within about 65 million light-years of the supergalactic plane. Viewed face-on, that slice shows the filaments, walls and voids clearly, the way astronomers usually draw them. The empty wedges you'll see crossing it are the "zone of avoidance": directions that lie behind our own Milky Way's dusty disk, where galaxies are hard to see, not missing.

The microwave map is built from NASA's WMAP satellite (7-year V and W bands, at about 2° resolution) by combining two frequencies so most of the Milky Way's own microwave glow cancels out. A band along our galaxy's plane, where that glow still swamps the signal, is filled in smoothly and isn't real data.

Search

The search box at the top of the menu (or its microphone button, where the browser supports speech recognition) finds any planet, moon, dwarf planet, asteroid, comet, spacecraft, star or galaxy by name. Stars can be found by proper name (Vega), Greek-letter name (Alpha Lyrae), Flamsteed number or catalog number; galaxies by common name (Andromeda Galaxy), Messier number (M31) or catalog name (NGC 224). Choosing a result flies the camera there. Each object's card has a Wikipedia button that opens its article in a new tab.

The hidden band behind our galaxy

Dust in the Milky Way's disk hides everything beyond it within about 8° of its plane, so surveys like the 2MASS Redshift Survey have almost no galaxies there: astronomers call it the zone of avoidance. From inside our galaxy that matches what we see. But fly out and look back at the Milky Way from the side, and the gap shows up as an unnatural empty band behind it. Solaris fills that band with about 6,500 stand-in galaxies, at the same range of distances as the real ones but in random directions, and shows them only when you're outside our galaxy's disk. They're illustrative: the real galaxies there exist, but most haven't been mapped. You can turn them off under View.

Pictures of stars and galaxies

Cards for stars, galaxies, clusters and nebulae have Show pictures of this. It shows the spot as photographed by the Digitized Sky Survey, a full photographic map of the sky (via the CDS hips2fits service), so even the 43,000 survey galaxies have a picture. It also searches the ESA/Hubble and ESA/Webb archives by name and shows any images they hold, each linking to the full image and its story.

No center, no edge

Solaris is centered on the Sun only because every distance in it was measured from here. Nothing makes our place special. On scales of hundreds of millions of light-years the universe is the same everywhere and in every direction (the cosmological principle), and it has no center and no edge. The Big Bang wasn't an explosion from a point; space itself has been expanding everywhere at once, so every galaxy sees every other galaxy moving away from it, faster the farther it is.

Under No center, no edge, choose where to stand, slide cosmic time, and press Play the expansion: arrows show each galaxy receding from your chosen spot. Switch to standing in the Andromeda Galaxy, the Coma Cluster or any galaxy's card (Stand here) and play it again: the picture is the same from everywhere. Bound systems such as our galaxy don't stretch, so the Milky Way is carried along as one lump. Run time backward and everything draws together evenly, with no central point; at the beginning, all of space was hot and dense, not a fireball sitting somewhere. The galaxies shown are today's, placed where the expansion would put them; real galaxies were also younger and different then.

The cosmic time slider runs from a billion years after the Big Bang to 10¹⁰⁶ years, deep into the future. Dark energy makes the expansion speed up, so within about 100 to 150 billion years every galaxy beyond our own merged group has slipped over the horizon. After that, the story is one of fading: the microwave background cools past detection, star formation ends around 10¹⁴ years, dead stars drift apart, black holes evaporate, and by about 10¹⁰⁰ years the universe is cold, dark and nearly empty. The captions follow the standard picture, after Fred Adams and Gregory Laughlin's "five ages of the universe"; the farthest dates depend on physics, such as whether protons decay, that isn't yet settled.

The edge of the observable universe is a horizon, not a wall: light has had only about 13.8 billion years to reach us while space stretched, so we can see out to about 46 billion light-years in every direction. Stand at MoM-z14, near our horizon, and Solaris draws its own observable universe, just as large, with our Milky Way near its edge. What lies beyond is an open question. Space may go on forever, or be finite but unbounded, curving back on itself; measurements so far show it is very close to flat. Either way, there's no edge to sit next to.

Show how we're moving adds arrows for the Sun's 230 km/s orbit around the galaxy and our motion through the universe, about 370 km/s for the Sun and 620 km/s for the Local Group relative to the microwave background. That motion makes the microwave sky about a thousandth warmer ahead of us than behind, which astronomers normally remove from their maps. And from Alpha Centauri, TRAPPIST-1 or Vega, our Sun is just one more star.

Powers of ten

The readout in the bottom-right corner shows the height of your view as a power of ten meters, with a dot on a strip running from the Planck length (10⁻³⁵ m) to the edge of the observable universe (about 10²⁷ m); the tick marks one meter, our own scale. With Powers-of-ten zoom on (under View), every wheel click is a tenth of a power of ten and pinching works the same way everywhere, so the zoom itself is a true-to-scale ruler: about 180 clicks from the Sun to the edge of the observable universe, and about 440 from the Sun down to the Planck length.

The scale bar

The bar in the corner always shows a round length at the distance you're looking: kilometers up close, astronomical units among the planets, and light-years among the stars. Beneath it, a picture and a comparison change as you zoom, from Earth's width and the Earth–Moon distance up to the distance to the galaxy's center, along with how long light takes to cross that length.

Forming a new system: what you are looking at

Every glowing point is a grain of the cloud. At the start they fill a slowly spinning ball around a young star. Gravity pulls them in, and as they fall they spin faster, the way a skater does when she pulls in her arms. Material can fall freely along the spin axis, but its spin keeps it from falling straight in from the sides, so the ball flattens.

The flattening needs one more ingredient: collisions. Grains falling from above and below the midplane keep running into each other. Each collision cancels some of their up-and-down motion, but the spin they share has nowhere to go. After enough collisions nearly everything orbits in one thin plane, in one direction. That is why the planets of our Solar System, and of most systems astronomers have found, orbit close to a single plane. Turn collisions off and the cloud stays a puffy, tumbling ball.

How planets form here

Once the disk is dense enough, the densest clumps become planet seeds. A seed starts with no mass and sweeps up dust that comes within part of its Hill radius, the region where its own gravity beats the star's tidal pull. Each grain it captures adds its mass and its momentum, so the planet's orbit is the average of everything it swallowed.

Growing planets clear gaps in the disk, tug on each other, scatter, merge when they collide, and sometimes get thrown into the star or out of the system. A planet is marked stable, and its orbit is drawn as a thin line, once it has gone three full orbits without a close encounter or a merger, its orbit size has varied by less than 2%, and its orbit's stretch (eccentricity) has stayed steady and below 0.5.

Planets are named the way astronomers name exoplanets: the star is Solaris, and its planets are lettered b, c, d and so on in the order they formed.

Comets

When a planet's gravity flings a grain onto a long, stretched orbit that still belongs to the star, it becomes a comet. Comets carry no mass in the simulation; they simply ride the star's and planets' gravity. Near the star the Sun's heat makes a real comet boil off gas and dust, so here the tail grows as the comet comes in, and always points away from the star. The blue strand is the gas tail, blown straight back; the paler, curving strand is the dust tail, which lags behind along the orbit. The Launch a comet button drops one in from far out on a random tilt, like a comet arriving from the Oort cloud.

A short history of the idea

In 1755 Immanuel Kant proposed that the Sun and planets condensed from a single rotating cloud. Pierre-Simon Laplace independently made the same argument in 1796, and their "nebular hypothesis" explained why the planets orbit in one plane and one direction. In 1878 George William Hill worked out the zone around a body in which its gravity dominates, now called the Hill sphere. In 1950 Jan Oort argued that long-period comets come from a vast, distant shell of icy bodies, scattered there by the giant planets.

In 1969 Viktor Safronov showed how dust could grow into kilometer-sized planetesimals and then into planets, the core of the modern picture. In 2005 the "Nice model" showed how the giant planets could have migrated and rearranged the early Solar System. And in 2014 the ALMA telescope array photographed the disk around the young star HL Tauri: a flat disk scored with dark rings, gaps that are thought to be carved by planets forming inside it. It looks a lot like the gaps you will see here.

Using Our Solar System

Pick a speed and press Forward or Backward. The date at the top of the menu follows along.
Type a date and time to jump there, or press Now to return to the present. The Halley 1986 and Apophis 2029 buttons jump to two famous visits.
Click a body in the scene or in the Bodies list. Clicking it in the list also zooms the camera to it and follows it; Zoom in on its card does the same.
Zoom in on Jupiter or Saturn to see their moons appear, and on Saturn to see its rings.
Press Milky Way under Zoom through space to fly from the planets out to the whole galaxy, then Inner planets to fly back. Watch the scale bar as you go.
Double-tap (or double-click) a body to zoom to it and follow it. Double-tap empty space to get back to the starting view if you've zoomed far out.

Forming a new system

Let it run. In the first few simulated years the cloud collapses; the thickness readout falls from about 0.7 toward a few hundredths as the disk forms.
Watch the planet list. Seeds appear as the disk gets dense, then grow, merge and scatter. "Settling" turns to "Stable" once an orbit stops changing.
Click or tap a planet, in the scene or in the list, to see its mass, age and orbit. Follow keeps it centered while the camera moves with it.
Try Launch a comet, then follow it through its closest pass by the star.
Change the cloud under New cloud and restart to see how spin, size and mass change the system you get.

Keys in Our Solar System: Space pause, [ and ] slower and faster, B backward or forward, N now, F follow, Z zoom to the selected body, L all names off and on.

Keys while forming a system: M menu, Space pause, R restart, C collisions on or off, K launch a comet, F follow the selected planet, Esc deselect.

Things to try

Set Initial spin near zero. With no spin to hold up a disk, almost everything falls straight into the star.
Color by where they started. Dust from the poles (amber) ends up in the same disk as dust from the equator (teal).
Raise Collision strength. The disk acts more viscous and drains into the star faster, the way real disks feed their stars.
Raise Cloud mass for giant planets, or lower it for a quieter system of small ones.
Switch sizes to True scale. The planets shrink to specks: space really is that empty.

Units and scale

Distances are in astronomical units (AU, the Earth–Sun distance) and the star's mass is in Suns, so one simulated year is one orbit at 1 AU around a one-Sun star. Masses are shown in Earths, or in Jupiters for the big ones. By default the star and planets are drawn far larger than life so you can see them. At true scale the Sun is 0.005 AU across and Jupiter 0.0005 AU, so even at the closest zoom they would be smaller than a pixel; true-scale mode draws them at their real size but never smaller than two pixels.

How realistic is it?

The big picture is right: the flattening, most of the mass ending up in the star, dust draining inward, planets clearing gaps, scattering, merging, ejecting their neighbors and finally settling into stable orbits. The details are heavily simplified so it can run live in a browser:

	Real systems	Solaris
Cloud size	A collapsing core is about 10,000 AU across; its disk about 100 AU	A cloud 4 to 30 AU in radius; the disk only a few times smaller
Time	The collapse takes about 100,000 years; planets take millions to tens of millions	Tens to hundreds of simulated years
The star	Forms from the collapse itself	Present from the start, fixed in place
Planet growth	Dust sticks into pebbles, then kilometer-sized planetesimals, then embryos, then planets	A dense clump becomes a seed that sweeps up dust directly

No self-gravity. The grains feel the star and the planets but not each other, so the disk can't pull on planets and planets don't migrate inward the way hot Jupiters are thought to.
No gas, pressure or temperature. There is no snow line, so nothing separates small rocky planets near the star from icy giants farther out.
Collisions are an average. Grains don't bounce off each other one by one; grains sharing a small cell of space nudge their velocities toward the cell's average. That keeps momentum but removes random motion, which is what real collisions and gas drag do on the whole.
Enlarged targets. The star swallows anything within 0.35 AU, and planets collide using their enlarged drawn sizes. Both keep the time steps manageable but make collisions more common than in reality.
Comets are passive. They lose no material and don't affect anything else.

How it works

Everything runs on your graphics card through WebGPU. For every step, a compute pass sorts all the grains into a three-dimensional grid of cells and adds up each cell's momentum. Graphics cards can't add decimal numbers safely from many threads at once, so velocities are stored as whole numbers in fixed point. A second pass moves every grain: gravity from the star and planets, the collision nudge toward its cell's average, any capture by a planet, and the step forward in time. Other passes look for dense clumps that could seed planets, for grains flung onto comet orbits, and add up the statistics shown in the menu.

The planets and comets are few enough to follow exactly on the main processor. Their gravity on each other is calculated directly, and mergers combine their mass and momentum. Every frame each planet's orbit is worked out from its position and velocity, which is what the stability test, the orbit lines and the details card use.

Credits

Planet positions from the JPL Solar System Dynamics group's approximate planetary elements (Standish and Williams). Small-body orbits from the JPL Small-Body Database and published elements.

Stars from the HYG database v4.1 by David Nash (astronexus.com), compiled from the Hipparcos, Yale Bright Star and Gliese catalogs. Deep-sky object positions, brightnesses and sizes from the OpenNGC catalog by Mattia Verga (CC BY-SA 4.0). Constellation figures from Stellarium's modern sky culture (Stellarium team, CC BY-SA 4.0). Cosmic microwave background from NASA's Wilkinson Microwave Anisotropy Probe (WMAP Science Team), using the low-resolution maps distributed with the healpy software. Distant galaxies from the 2MASS Redshift Survey (Huchra et al. 2012), with distances from the NANOGrav galaxy catalog (Arzoumanian et al. 2021). Galaxies from the Catalog & Atlas of Local Volume galaxies (Karachentsev, Makarov & Kaisina 2013, with later updates).

Earth imagery: NASA Visible Earth, Blue Marble: Next Generation (Reto Stöckli, NASA Earth Observatory) and Black Marble city lights (NASA Earth Observatory, Suomi NPP VIIRS). Daily clouds: NASA Global Imagery Browse Services (GIBS) and NASA Worldview, VIIRS Corrected Reflectance from Suomi NPP and NOAA-20, via NASA LANCE. Sun, Mercury, Venus, Moon, Mars, Jupiter, Saturn, Uranus and Neptune maps: Solar System Scope, CC BY 4.0, based on NASA mission data. Satellite orbits: CelesTrak (Dr. T. S. Kelso), propagated with the satellite.js SGP4 library. Spacecraft trajectories: NASA JPL Horizons. Rotation of the planets and moons: IAU Working Group on Cartographic Coordinates and Rotational Elements.

Physics after the nebular hypothesis of Kant and Laplace, Hill's sphere of influence, and Safronov's theory of planet growth, much simplified.

Created by Jason Buchheim of Odyssey Expeditions: marine biologist, ocean photographer and immersive-media developer, building odd machines for curious minds.

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