PORTAL_Solar_System - Wikiparency

<div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html" data-title="The Solar System explorer"></div> *Try: set the speed to 10 years/s and watch the inner planets race while Neptune barely moves; open the object menu and step through the states with the [ and ] keys; press t for the tour, which walks the states in the order of this page.* **The Solar System** is the Sun and everything bound to it by gravity: eight planets, nine dwarf planets, hundreds of moons, more than a million minor planets and thousands of comets, out to a theorized cloud of icy bodies a third of the way to the nearest star. This portal is its front door on Wikitube, article face [[Solar_System]]. It runs in thirty sections from the definition of a planet, through the Sun and every population outward, to the edge of the heliosphere and the Sun's place in the galaxy, and every section opens the same instrument, the Solar System explorer, in the state that belongs to it. Sibling rooms: [[PORTAL_Physics]] (the mechanics under every orbit), [[PORTAL_Chemistry]] (what the bodies are made of) and [[PORTAL_Energy]] (the Sun as a source). Index: [[PORTAL_INDEX]]. ## How to read this page The page follows the outline of the Solar System article in seven parts: the system as a whole, the Sun, the inner Solar System, the outer Solar System, the trans-Neptunian region, the populations that do not keep their orbits, and the edge of the Sun's influence with the neighborhood beyond it. Each section is a short summary of a subject that has its own full article, named in the line under the heading, with its See-also articles beside it; many of those articles are not written yet, and their links are the build list. Each section ends with the sections it connects to, so the page reads straight through or from any point. Every section carries the same microsim, one three.js scene called the Solar System explorer, opened in that section's state: `?obj=Mars` for Mars, `?obj=kuiper` for the Kuiper belt, `?view=orbits` for the orbits view. The planets sit at their real positions for the date on the year slider (JPL elements, valid 1800 to 2050), and every named small body moves on its real JPL orbit. Distances are drawn on a logarithmic scale by default, the only way the Sun and the Oort cloud fit one screen; the scale menu switches to true scale where true scale can show the subject, and for a planet with moons it opens the planet's own frame. Drag to orbit, scroll to zoom, press *l* for labels, *o* for orbits, *space* to pause and *r* to reset. What is illustrative is said on screen: the random points that stand for each belt and cloud (their ranges are real), the body sizes in log mode, the spherical shape of the heliosphere boundaries and the starting phases of the moons. ## Part I — The system as a whole The first seven sections look at the Solar System all at once: what counts as a member, how it formed, what it is made of, how its bodies move, how far apart they are, where water could stay liquid, and how it compares with the planetary systems found around other stars. Each uses one of the explorer's whole-system views rather than a single body. ### Definition *Main article: [[IAU_definition_of_planet]] · See also: [[Dwarf_planet]], [[Small_Solar_System_body]], [[Clearing_the_neighbourhood]]* The Solar System is the Sun and every body its gravity holds in orbit.[^ss] The pair's infobox counts one star, eight planets, nine dwarf planets, 758 known moons, more than 1.46 million minor planets and 4,629 comets.[^ss] The line between the first two kinds of orbiting body is a rule, not a measurement: the International Astronomical Union calls a body a planet when it orbits the Sun, is massive enough to pull itself round, and has [[Clearing_the_neighbourhood|cleared the neighbourhood]] around its orbit; a body that meets only the first two tests is a dwarf planet.[^iau] Pluto is the best-known casualty of that third test.[^iau] In this state the explorer colours every drawn body by class, gold for the dwarf planets, blue for the planets and grey for the small bodies, and the readout prints the pair's counts, so the census and the picture sit side by side. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=census&embed=1" data-title="The census in the Solar System explorer"></div> *Try: set the speed to 1 year/s and watch the nine dwarf planets move at very different rates; press l to hide the labels and read the classes by colour alone; switch the show menu to small bodies.* Connects to: [[#Composition|Composition]] · [[#Sun|Sun]] · [[#Asteroid belt|Asteroid belt]] · [[#Pluto and the dwarf planets of the belt|Pluto and the dwarf planets of the belt]] ### Formation and evolution *Main article: [[Formation_and_evolution_of_the_Solar_System]] · See also: [[Protoplanetary_disk]], [[Nice_model]], [[Grand_tack_hypothesis]], [[Late_Heavy_Bombardment]]* The Solar System formed at least 4.568 billion years ago, when a region of a large molecular cloud collapsed under its own gravity.[^ss] As it fell inward it spun faster, flattened into a [[Protoplanetary_disk|protoplanetary disc]] roughly 200 AU across and heated a dense protostar at the centre.[^ss] Close to that young star only rock and metal could stay solid, so the inner planets are small and dense; farther out, ices condensed as well, and the giant planets grew large enough to hold hydrogen and helium.[^ss] The same arrangement is still written into the orbits today, and it is what this state draws: the planets coloured rocky, gas giant or ice giant, with the frost line marked as a ring between Mars and Jupiter.[^fl] The Sun will stay on the main sequence for roughly 5 billion more years before it swells into a red giant.[^ss] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=composition&embed=1" data-title="Composition in the Solar System explorer"></div> *Try: set the year to 1800 and the speed to 100 years/s and watch the architecture hold steady across two and a half centuries; press o to hide the orbits and see the rock-to-ice gradient in the bodies alone.* Connects to: [[#Composition|Composition]] · [[#Orbits|Orbits]] · [[#Oort cloud|Oort cloud]] ### Composition *Main article: [[Frost_line_(astrophysics)]] · See also: [[Terrestrial_planet]], [[Gas_giant]], [[Ice_giant]]* The Sun holds 99.86 percent of the Solar System's mass; the four giant planets hold 99 percent of what is left, and Jupiter and Saturn together more than 90 percent.[^ss] Everything else, the terrestrial planets, dwarf planets, moons, asteroids and comets, adds up to less than 0.002 percent.[^ss] Composition follows distance from the Sun. Near it only materials with high melting points could survive the early heat, so the inner bodies are silicate and metal; beyond the [[Frost_line_(astrophysics)|frost line]] water, ammonia and methane stayed solid and were swept up into the giants and the icy bodies.[^ss] The pair places the frost line at roughly five times Earth's distance; the Frost line article gives about 2.7 AU for the time when planetesimals formed, and that is the ring the explorer draws.[^fl] Colours in this state follow the same split. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=composition&embed=1" data-title="Composition in the Solar System explorer"></div> *Try: press o to hide the orbits and read the rock-to-ice split in the body colours alone; drag to look edge-on and see how thin the planetary disc is; set the speed to 10 years/s.* Connects to: [[#Definition|Definition]] · [[#Formation and evolution|Formation and evolution]] · [[#Distances and scales|Distances and scales]] · [[#Habitability|Habitability]] · [[#Sun|Sun]] · [[#Jupiter|Jupiter]] ### Orbits  *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/matter/Kepler's_laws_of_planetary_motion.html" data-title="Kepler's laws of planetary motion"></div>  *Main article: [[Orbit]] · See also: [[Kepler's_laws_of_planetary_motion]], [[Ecliptic]]* The planets and most other large bodies orbit close to one plane, the invariable plane, and Earth's own orbital plane, the ecliptic, sits near it.[^ss] Almost everything orbits in the same direction the Sun turns, counter-clockwise seen from above Earth's north pole; Halley's Comet is a prominent exception.[^ss] To a good first approximation [[Kepler's_laws_of_planetary_motion|Kepler's laws]] describe these orbits: ellipses with the Sun at one focus, swept at a rate that keeps equal areas in equal times, with the square of the period proportional to the cube of the semi-major axis.[^ss] The explorer computes every planet's position from JPL's elements for the chosen date and every named small body from its own JPL elements.[^jpl][^sbdb] In this state the camera drops to a low angle, so Pluto's 17-degree tilt, Eris's 44 degrees and Halley's backward, 162-degree orbit stand out against the flat planetary disc.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=orbits&embed=1" data-title="The orbits in the Solar System explorer"></div> *Try: set the speed to 1 year/s and compare how fast Mercury and Neptune move; press o to hide and restore the orbits; drag upward until the orbits stack edge-on.* Connects to: [[#Formation and evolution|Formation and evolution]] · [[#Distances and scales|Distances and scales]] · [[#Comparison with extrasolar systems|Comparison with extrasolar systems]] · [[#Mercury|Mercury]] · [[#Pluto and the dwarf planets of the belt|Pluto and the dwarf planets of the belt]] · [[#Comets|Comets]] ### Distances and scales *Main article: [[Astronomical_unit]] · See also: [[Solar_System_model]]* The astronomical unit, fixed in 2012 at exactly 149,597,870,700 metres, is the natural yardstick here.[^au] Light crosses one AU in 499.0 seconds, so sunlight reaches Earth in 8.3 minutes, Jupiter in 43 minutes and Neptune, 30 AU out, in about 4.2 hours.[^au][^wts] The gaps grow with distance: Venus lies 0.33 AU beyond Mercury, but Neptune lies 10.5 AU beyond Uranus.[^ss] No single linear drawing shows both the inner planets and the Oort cloud, which is why the explorer runs in two modes. The default is logarithmic, a size-honest map of direction with compressed distance; this state switches to true scale out to 35 AU and draws a light-time ruler along the axis, each tick labelled with its distance and travel time. A [[Solar_System_model|Solar System model]] built across a city makes the same point at walking pace. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=scale&embed=1" data-title="Distances at true scale in the Solar System explorer"></div> *Try: read the light-time on each tick of the ruler; set the speed to 1 year/s and watch the inner planets blur while Neptune barely moves; drag to look down on the ruler from above.* Connects to: [[#Composition|Composition]] · [[#Orbits|Orbits]] · [[#Habitability|Habitability]] · [[#Edge of the heliosphere|Edge of the heliosphere]] · [[#Celestial neighborhood|Celestial neighborhood]] ### Habitability *Main article: [[Habitable_zone]] · See also: [[Earth]], [[Solar_wind]]* The habitable zone is the range of distances where a planet could keep liquid water on its surface.[^ss] Estimates for the Sun vary widely; a 2013 revision of the classic Kasting model puts it between 0.99 and 1.67 AU, a band that holds Earth and Mars, while Kasting's own conservative limits of 1993 were 0.95 to 1.37 AU.[^hz] Sunlight is not the only factor. The Sun's magnetic field and the planets' own fields shield surfaces from cosmic rays, and water may also persist in oceans below the surfaces of some bodies far outside the zone.[^ss] [[Earth]] is the only place where life is known to exist.[^ss] In this state the explorer draws the habitable zone as a green annulus and the frost line as a thin blue ring, both in the plane of the ecliptic, so the reader can watch the inner planets pass through or stay clear of them.[^hz][^fl] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=zones&embed=1" data-title="The habitable zone and the frost line in the Solar System explorer"></div> *Try: set the speed to 1 month/s and watch Mars stay inside the green band even at aphelion, 1.67 AU; watch Venus stay inside the band's inner edge; drag to look straight down on the two rings.* Connects to: [[#Composition|Composition]] · [[#Distances and scales|Distances and scales]] · [[#Earth and the Moon|Earth and the Moon]] ### Comparison with extrasolar systems *Main article: [[Planetary_system]] · See also: [[Planet_Nine]]* Surveys by the Kepler telescope sort planetary systems into three kinds: similar, with planets of like size at like spacings, ordered, with mass rising outward, and mixed.[^ss] The Solar System is ordered, as are 37 percent of observed systems; similar systems are the majority at 59 percent.[^ss] It is unusual in two ways. It has no planet inside the orbit of Mercury, and it has no super-Earth, a planet of one to ten Earth masses and the most common type found in the galaxy.[^ss] The hypothetical [[Planet_Nine]], if it exists, could be one, far out at the edge of the system; it is a hypothesis and the explorer does not draw it.[^ss] This state reuses the orbits view: near-circular planetary orbits, the rocky planets close in, the giants far out, and a wide empty gap between Earth-sized and Neptune-sized worlds. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=orbits&embed=1" data-title="The orbits in the Solar System explorer"></div> *Try: set the speed to 10 years/s and count how many orbits Mercury completes while Jupiter completes one; drag to look straight down and judge how circular the planetary orbits are.* Connects to: [[#Orbits|Orbits]] · [[#Extreme trans-Neptunian objects|Extreme trans-Neptunian objects]] ## Part II — The Sun One section for the star that holds almost all of the mass and sets every orbit below. ### Sun *Main article: [[Sun]] · See also: [[Solar_wind]], [[Heliosphere]]* The Sun is a G2-type main-sequence star holding 332,900 Earth masses, 99.86 percent of all the mass in the Solar System.[^ss] Its core is hot and dense enough to fuse hydrogen into helium, and the energy that escapes is radiated mostly as visible light.[^ss] Its radius is 695,700 kilometres, 109 times Earth's, and its axis tilts 7.25 degrees from the ecliptic.[^wts][^sun] It formed as a population I star in one of the galaxy's spiral arms, richer in heavy elements than the older stars of the bulge and halo.[^ss] The [[Solar_wind|solar wind]] it blows outward fills the heliosphere out past 120 AU. In this state the explorer shows the Sun close up with a size ladder beneath it: the Sun's edge and the eight planets drawn at their true relative radii, where Earth is a dot beside Jupiter and Jupiter is small beside the Sun.[^fs] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Sun&embed=1" data-title="Sun in the Solar System explorer"></div> *Try: compare Jupiter's disc with the Sun's edge on the size ladder; read the light-time to Earth in the readout as the date changes; set the speed to 1 year/s and watch that number swing between perihelion and aphelion.* Connects to: [[#Definition|Definition]] · [[#Composition|Composition]] · [[#Edge of the heliosphere|Edge of the heliosphere]] ## Part III — Inner Solar System The four rocky planets, the Moon, the main asteroid belt and the asteroid populations that stray from it: everything inside the frost line, in order outward from the Sun. ### Mercury *Main article: [[Mercury_(planet)]]* Mercury is the smallest planet and the closest to the Sun, ranging from 0.31 to 0.59 AU.[^ss] Its orbit is the most eccentric of the eight, e = 0.206, carrying it from 46.0 million kilometres at perihelion to 69.8 million at aphelion, around the Sun once every 88 days.[^fs] Its equatorial surface swings from about -170 C at night to 420 C in sunlight, and the planet has no natural satellites.[^ss] It turns once every 1,407.6 hours, so slowly that a solar day there lasts 4,222.6 hours, longer than its year.[^fs] In this state the explorer highlights Mercury's orbit, marks perihelion and aphelion with ticks and draws a faint shadow of the orbit on the ecliptic, which shows its 7-degree tilt. Next door lies [[Venus]], whose orbit is almost perfectly round. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Mercury&embed=1" data-title="Mercury in the Solar System explorer"></div> *Try: set the speed to 1 month/s and watch Mercury speed up at the perihelion tick and slow at aphelion; read r and v in the readout as it goes round; switch the scale to true to see the off-centre ellipse without the log map.* Connects to: [[#Orbits|Orbits]] · [[#Venus|Venus]] ### Venus *Main article: [[Venus]]* Venus orbits between 0.72 and 0.73 AU, on the most nearly circular orbit of the planets, e = 0.007.[^ss][^fs] It spins backwards: its rotation period is -5,832.5 hours, a 243-day turn that is longer than its 224.7-day year.[^fs] Its thick atmosphere is mainly carbon dioxide, with a surface pressure ninety times that at Earth's sea level, and its greenhouse effect holds the mean surface temperature at 464 C.[^ss][^fs] Venus has no magnetic field and no moons.[^ss] Its axis is tilted 177.4 degrees, which is the same statement as the retrograde spin: the pole the explorer draws through the planet points almost straight down.[^fs] In this state the orbit is highlighted with perihelion and aphelion ticks that sit almost on top of each other, the mark of a nearly round orbit, in contrast with its neighbour [[Mercury_(planet)|Mercury]]. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Venus&embed=1" data-title="Venus in the Solar System explorer"></div> *Try: set the speed to 1 month/s and watch Venus overtake Earth roughly every 19 months; drag close to the planet to see the pole line pointing down; compare its apsis ticks with Mercury's.* Connects to: [[#Mercury|Mercury]] · [[#Earth and the Moon|Earth and the Moon]] ### Earth and the Moon  *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Moon&embed=1" data-title="The Moon in the Solar System explorer"></div>  *Main article: [[Earth]] · See also: [[Moon]]* Earth orbits between 0.98 and 1.02 AU and is the only place where life and surface liquid water are known to exist.[^ss] Its axis tilts 23.4 degrees, which gives it seasons, and its magnetic field shields the surface from radiation.[^fs][^ss] The planet in this explorer is the Earth-Moon barycentre, the balance point JPL's elements track, which lies about 5,000 kilometres from Earth's centre, three-quarters of the way to its surface.[^jpl][^mo] The Moon orbits 384,399 kilometres out once every 27.32 days and has a radius of 1,737.4 kilometres.[^mo] With scale set to true the explorer switches to Earth's local frame: Earth at its true radius and the [[Moon]] at its true distance and period, its starting phase marked as illustrative. In the default log view the Moon is hidden inside Earth's dot, which is itself a statement about distances. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Earth&embed=1" data-title="Earth and the Moon in the Solar System explorer"></div> *Try: switch the scale to true to open the local frame and count the Moon's orbits against the date; set the speed to 1 day/s and watch one lunar month pass in 27 seconds.* Connects to: [[#Habitability|Habitability]] · [[#Venus|Venus]] · [[#Mars|Mars]] ### Mars  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://editor.p5js.org/sciencenibber/full/p472uEZ32" data-title="Mars"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Phobos&embed=1" data-title="Phobos in the Solar System explorer"></div> </div>  *Main article: [[Mars]] · See also: [[Moons_of_Mars]]* Mars orbits between 1.38 and 1.67 AU on an orbit with e = 0.094: 206.7 million kilometres from the Sun at perihelion and 249.3 million at aphelion.[^ss][^fs] That spread is why close approaches to Earth differ so much from one opposition to the next. On 28 August 2003 Mars and Earth lined up near Mars's perihelion, and the explorer's ephemeris places them within a tenth of a degree of each other in heliocentric longitude on that date.[^jpl][^wts] A Mars year lasts 687 days; the planet's radius is about half Earth's, and its thin carbon-dioxide atmosphere has a surface pressure 0.6 percent of Earth's.[^ss][^fs] Its two small moons orbit close in: Phobos at 9,377 kilometres in 7.66 hours, Deimos at 23,460 kilometres in 30.31 hours.[^mm] Beyond Mars lies the [[Asteroid_belt|asteroid belt]]. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Mars&embed=1" data-title="Mars in the Solar System explorer"></div> *Try: drag the year to 2003.67 and see Earth and Mars side by side; set the speed to 1 month/s and watch Earth lap Mars every 26 months; switch the scale to true to open the Mars local frame with Phobos and Deimos.* Connects to: [[#Earth and the Moon|Earth and the Moon]] · [[#Asteroid belt|Asteroid belt]] ### Asteroid belt  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Ceres&embed=1" data-title="Ceres in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Vesta&embed=1" data-title="4 Vesta in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Pallas&embed=1" data-title="2 Pallas in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Hygiea&embed=1" data-title="10 Hygiea in the Solar System explorer"></div> </div>  *Main article: [[Asteroid_belt]] · See also: [[Ceres_(dwarf_planet)]], [[4_Vesta]], [[2_Pallas]], [[10_Hygiea]], [[Kirkwood_gap]]* The asteroid belt is a torus between 2.3 and 3.3 AU, between the orbits of Mars and Jupiter.[^ss] Its bodies are thought to be leftovers that never gathered into a planet because Jupiter's gravity kept stirring them.[^ss] It holds tens of thousands, possibly millions, of objects over a kilometre across, yet its total mass is unlikely to exceed a thousandth of Earth's, and spacecraft cross it without incident.[^ss] The largest body, Ceres, is its only dwarf planet, 940 kilometres across.[^ss] Where an asteroid's period would be a simple fraction of Jupiter's, the belt is emptied: the [[Kirkwood_gap|Kirkwood gaps]] at 2.502, 2.825, 2.958 and 3.279 AU mark the 3:1, 5:2, 7:3 and 2:1 resonances.[^kg] The explorer draws the belt as a sampled cloud with those four gaps cut out; the points are illustrative, while Ceres, Vesta, Pallas and Hygiea move on their real orbits.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=belt&embed=1" data-title="Asteroid belt in the Solar System explorer"></div> *Try: drag down to look at the belt face-on and find the gaps; set the speed to 1 year/s and watch the inner edge of the cloud outrun the outer edge; press l to hide the labels.* Connects to: [[#Definition|Definition]] · [[#Mars|Mars]] · [[#Trojans, Hildas and near-Earth objects|Trojans, Hildas and near-Earth objects]] · [[#Kuiper belt|Kuiper belt]] · [[#Meteoroids, meteors and dust|Meteoroids, meteors and dust]] ### Trojans, Hildas and near-Earth objects  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=hildas&embed=1" data-title="The Hilda asteroids in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=neo&embed=1" data-title="Near-Earth objects in the Solar System explorer"></div> </div>  *Main article: [[Asteroid]] · See also: [[Jupiter_trojan]], [[Hilda_asteroid]], [[Near-Earth_object]]* Not every asteroid stays in the main belt. Trojans sit near a planet's Lagrange points, 60 degrees ahead of it (L4) or 60 degrees behind (L5), and every planet except Mercury is known to have at least one; Jupiter's trojans are roughly as numerous as the main belt.[^ss] The largest, 624 Hektor, is about 203 kilometres across.[^jt] The Hilda asteroids orbit three times for every two orbits of Jupiter and gather in three linked clusters between Jupiter and the belt.[^ss] Near-Earth asteroids come close to Earth's orbit, over 37,000 of them known, some large enough to count as potentially hazardous.[^ss] In the explorer the two trojan swarms travel with Jupiter as lobes, the Hildas keep their triangle, and [[Near-Earth_object|near-Earth objects]] such as Apophis, Bennu and Eros move on their real JPL orbits while the clouds around them are illustrative samples.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=trojans&embed=1" data-title="Trojans, Hildas and near-Earth objects in the Solar System explorer"></div> *Try: set the speed to 1 year/s and watch both trojan swarms keep pace with Jupiter; switch the show menu to small bodies to hide the planets; drag to look down on the Hilda triangle.* Connects to: [[#Asteroid belt|Asteroid belt]] · [[#Jupiter|Jupiter]] · [[#Comets|Comets]] ## Part IV — Outer Solar System The four giant planets, their largest moons and rings, and the centaurs that cross between them. From here outward the log scale starts to matter. ### Jupiter  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Io&embed=1" data-title="Io in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Europa&embed=1" data-title="Europa in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Ganymede&embed=1" data-title="Ganymede in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Callisto&embed=1" data-title="Callisto in the Solar System explorer"></div> </div>  *Main article: [[Jupiter]] · See also: [[Galilean_moons]], [[Io_(moon)]], [[Europa_(moon)]], [[Ganymede_(moon)]], [[Callisto_(moon)]]* Jupiter, at 4.95 to 5.46 AU, is the largest and most massive planet: 1,898 x 10^24 kilograms, 318 times Earth.[^ss][^fs] Its cloud bands and storms, the Great Red Spot among them, move with the planet's fast rotation of 9.9 hours, and its magnetosphere is strong enough to raise auroras at its poles.[^ss][^fs] The pair counts 115 confirmed moons.[^ss] The four largest, the [[Galilean_moons|Galilean moons]], are the picture this state sells. Io circles in 1.769 days, Europa in 3.551, Ganymede in 7.155, and the three are locked in a 1:2:4 resonance; Callisto, at 16.69 days, sits outside it.[^io][^eu][^ga][^ca] Ganymede is the largest moon in the Solar System.[^ga] With scale set to true the explorer opens Jupiter's local frame at true relative distance, with the moons' periods real and their starting positions illustrative. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Jupiter&embed=1" data-title="Jupiter in the Solar System explorer"></div> *Try: switch the scale to true to open the local frame; set the speed to 1 day/s and count four Io orbits for every Ganymede orbit; drag to look at the moons edge-on.* Connects to: [[#Composition|Composition]] · [[#Trojans, Hildas and near-Earth objects|Trojans, Hildas and near-Earth objects]] · [[#Saturn|Saturn]] ### Saturn  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Saturn&scale=true&embed=1" data-title="Saturn in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Titan&embed=1" data-title="Titan in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Enceladus&embed=1" data-title="Enceladus in the Solar System explorer"></div> </div>  *Main article: [[Saturn]] · See also: [[Rings_of_Saturn]], [[Titan_(moon)]], [[Enceladus]]* Saturn orbits between 9.08 and 10.12 AU and, like Jupiter, is mostly hydrogen and helium.[^ss] Its axis tilts 26.7 degrees.[^fs] Its ring system, small particles of ice and rock orbiting over its equator, runs in the main rings from the inner edge of the C Ring at 74,658 kilometres from the planet's centre to the outer edge of the A Ring at 136,775 kilometres, with the narrow F Ring at 140,180.[^rs] The pair counts 293 confirmed moons.[^ss] [[Titan_(moon)|Titan]], the largest, orbits 1,221,870 kilometres out every 15.9 days; Enceladus orbits at 238,037 kilometres in 1.37 days.[^ti][^en] With scale set to true the explorer opens Saturn's local frame: the planet at its true radius, the main rings as a flat annulus in the tilted equatorial plane, the F Ring as a thin line, and both moons on their orbits. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Saturn&embed=1" data-title="Saturn in the Solar System explorer"></div> *Try: switch the scale to true and drag around to see the ring plane tilt; set the speed to 1 day/s and time one orbit of Enceladus; press o to hide the heliocentric orbits when you return to log scale.* Connects to: [[#Jupiter|Jupiter]] · [[#Uranus|Uranus]] ### Uranus *Main article: [[Uranus]]* Uranus orbits between 18.3 and 20.1 AU and, alone among the planets, rolls along its orbit on its side, with an axial tilt of 97.8 degrees.[^ss][^fs] Each pole points alternately toward and then away from the Sun over the orbit, which gives the planet extreme seasons.[^ss] Its upper clouds are a muted cyan, and beneath them its climate keeps several puzzles, among them an unusually low internal heat.[^ss] The planet spins in 17.2 hours in the retrograde sense the tilt implies, and one orbit takes 30,589 days.[^fs] The pair counts 29 confirmed moons, and the fact sheet lists a ring system.[^ss][^fs] In this state the explorer highlights the orbit and draws the pole line through the planet, lying almost in the plane of the orbit; compare it with Saturn's modest tilt or with [[Neptune]], the next planet out. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Uranus&embed=1" data-title="Uranus in the Solar System explorer"></div> *Try: drag close to Uranus and look at the pole line against the orbit; set the speed to 10 years/s and watch one 84-year orbit pass; compare with Saturn's pole in its own state.* Connects to: [[#Saturn|Saturn]] · [[#Neptune|Neptune]] ### Neptune  *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Triton&embed=1" data-title="Triton in the Solar System explorer"></div>  *Main article: [[Neptune]] · See also: [[Triton_(moon)]]* Neptune, at 29.9 to 30.5 AU, is the farthest known planet and marks the outer edge of the planetary region.[^ss] Its orbit is nearly circular, e = 0.010, and one trip around the Sun takes 59,800 days, almost 165 years.[^fs] Its atmosphere is a muted cyan with occasional dark storms, and its magnetic field is tilted 47 degrees.[^ss] The pair counts 16 confirmed moons.[^ss] The largest, [[Triton_(moon)|Triton]], orbits backwards, against Neptune's spin, 354,759 kilometres out every 5.88 days, the largest moon in the Solar System to do so.[^tr][^ss] Beyond Neptune the Kuiper belt begins, and Pluto's orbit dips inside Neptune's near perihelion. With scale set to true the explorer opens Neptune's local frame, where Triton's orbit is drawn with its retrograde sense; in the log view Neptune's orbit is the ring the belt wraps around. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Neptune&embed=1" data-title="Neptune in the Solar System explorer"></div> *Try: switch the scale to true and watch Triton run the opposite way to the planet's pole; in log scale set the speed to 100 years/s and watch Pluto slip inside Neptune's orbit.* Connects to: [[#Uranus|Uranus]] · [[#Centaurs|Centaurs]] · [[#Kuiper belt|Kuiper belt]] ### Centaurs *Main article: [[Centaur_(small_Solar_System_body)]]* Centaurs are icy, comet-like bodies whose semi-major axes lie between Jupiter's and Neptune's, from 5.5 to 30 AU.[^ss] They are former Kuiper belt and scattered disc objects that the outer planets have perturbed inward, and they are expected either to become comets or to be ejected from the Solar System.[^ss] Most are inactive and look like asteroids, but some show comet activity.[^ss] The first to be found, 2060 Chiron, grows a coma near perihelion and is also classified as comet 95P.[^ss] Its orbit has a = 13.7 AU and e = 0.38, crossing Saturn's path.[^sbdb] The explorer draws the centaurs as a sampled cloud between the giants, illustrative in its members but real in its range, and moves Chiron on its JPL orbit; propagated decades from its epoch, that position is approximate, because the [[Comet|comet-like]] path is steered by the planets it crosses. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=centaurs&embed=1" data-title="Centaurs in the Solar System explorer"></div> *Try: set the speed to 10 years/s and follow Chiron from near Saturn out toward Uranus; switch the show menu to clouds and boundaries to see the cloud without the planets.* Connects to: [[#Neptune|Neptune]] · [[#Kuiper belt|Kuiper belt]] · [[#Comets|Comets]] ## Part V — Trans-Neptunian region Past Neptune the Solar System becomes belts and clouds: the Kuiper belt and its dwarf planets, the scattered disc, the extreme objects whose orbits reach hundreds of AU, and the theorized Oort cloud that reaches a third of the way to the nearest star. ### Kuiper belt *Main article: [[Kuiper_belt]] · See also: [[Trans-Neptunian_object]], [[Classical_Kuiper_belt_object]], [[Plutino]], [[Resonant_trans-Neptunian_object]]* The Kuiper belt is a great ring of mostly icy debris between 30 and 50 AU.[^ss] It is estimated to hold more than 100,000 bodies over 50 kilometres across, yet its total mass is only a tenth to a hundredth of Earth's.[^ss] Many of its members have moons, and most orbit at substantial tilts.[^ss] The belt divides into the classical belt, from roughly 39.4 to 47.7 AU, whose members have no resonance with Neptune, and the [[Resonant_trans-Neptunian_object|resonant objects]], whose periods are simple fractions of Neptune's; the plutinos orbit twice for every three Neptune orbits.[^ss] In 2019 New Horizons flew past 486958 Arrokoth, a contact binary 32 kilometres long, the only Kuiper belt object visited apart from Pluto and its moons.[^kb] The explorer draws the belt as a sampled ring with the plutino band at 39.4 AU; the points are illustrative, Arrokoth's orbit is real.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=kuiper&embed=1" data-title="Kuiper belt in the Solar System explorer"></div> *Try: drag down to a low angle to see the belt's thickness; set the speed to 100 years/s and watch the plutinos keep their spacing from Neptune; press l to hide the labels.* Connects to: [[#Asteroid belt|Asteroid belt]] · [[#Neptune|Neptune]] · [[#Centaurs|Centaurs]] · [[#Pluto and the dwarf planets of the belt|Pluto and the dwarf planets of the belt]] · [[#Scattered disc|Scattered disc]] ### Pluto and the dwarf planets of the belt  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Charon&embed=1" data-title="Charon in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Haumea&embed=1" data-title="Haumea in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Makemake&embed=1" data-title="Makemake in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Orcus&embed=1" data-title="Orcus in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Quaoar&embed=1" data-title="Quaoar in the Solar System explorer"></div> </div>  *Main article: [[Pluto]] · See also: [[Charon_(moon)]], [[Haumea]], [[Makemake]], [[Orcus_(dwarf_planet)]], [[Quaoar]]* Pluto, the largest known Kuiper belt object, orbits between 29.7 and 49.3 AU on an orbit inclined 17 degrees to the ecliptic.[^ss] It is in a 2:3 resonance with Neptune, orbiting twice for every three Neptune orbits, and that resonance keeps the two apart even though Pluto's orbit dips inside Neptune's.[^ss] Pluto has five moons; the largest, [[Charon_(moon)|Charon]], orbits 19,596 kilometres from Pluto's centre every 6.39 days, and the pair's balance point lies outside Pluto.[^ss][^ch] Four more dwarf planets share the belt: Orcus, whose semi-major axis of 39.4 AU places it among the plutinos; Haumea; Quaoar, on a nearly circular orbit; and Makemake.[^ss][^sbdb] In this state the explorer highlights Pluto's orbit with perihelion and aphelion ticks and a shadow on the ecliptic; each of the other four has its own state with its own real JPL orbit.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Pluto&embed=1" data-title="Pluto and the dwarf planets of the belt in the Solar System explorer"></div> *Try: set the speed to 100 years/s and watch Pluto pass inside Neptune's orbit while Neptune is far away; switch the scale to true to open Pluto's local frame and watch Charon circle.* Connects to: [[#Definition|Definition]] · [[#Orbits|Orbits]] · [[#Kuiper belt|Kuiper belt]] ### Scattered disc  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Eris&embed=1" data-title="Eris in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Gonggong&embed=1" data-title="Gonggong in the Solar System explorer"></div> </div>  *Main article: [[Scattered_disc]] · See also: [[Eris_(dwarf_planet)]], [[Gonggong_(dwarf_planet)]]* The scattered disc overlaps the Kuiper belt but reaches out to near 500 AU and is thought to be the source of short-period comets.[^ss] Its members were thrown onto erratic orbits by Neptune's early outward migration: most have perihelia within the Kuiper belt and aphelia far beyond it, some more than 150 AU, at inclinations up to 46.8 degrees.[^ss] Two scattered-disc bodies are dwarf planets. [[Eris_(dwarf_planet)|Eris]], 25 percent more massive than Pluto and about the same size, ranges from 38.3 to 97.5 AU on an orbit tilted 44 degrees, and its discovery fed the debate that produced the planet definition.[^ss] Gonggong reaches about 100 AU.[^sbdb] The explorer draws the disc as a sampled cloud of long, tilted ellipses, illustrative in its members, with Eris and Gonggong on their real orbits; the heliosphere's inner shells show where the solar wind gives way. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=scattered&embed=1" data-title="Scattered disc in the Solar System explorer"></div> *Try: drag to an edge-on view and compare Eris's tilt with the Kuiper belt; set the speed to 100 years/s and watch Eris crawl near aphelion.* Connects to: [[#Kuiper belt|Kuiper belt]] · [[#Extreme trans-Neptunian objects|Extreme trans-Neptunian objects]] · [[#Comets|Comets]] ### Extreme trans-Neptunian objects  *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Sedna&embed=1" data-title="Sedna in the Solar System explorer"></div>  *Main article: [[Extreme_trans-Neptunian_object]] · See also: [[Sedna_(dwarf_planet)]], [[Sednoid]], [[Detached_object]], [[Planet_Nine]]* Some bodies orbit so far out that the known giant planets barely touch them. These extreme trans-Neptunian objects have semi-major axes of at least 150 to 250 AU.[^ss] The [[Sednoid|sednoids]], with perihelia beyond 50 to 60 AU, are too far from Neptune to be strongly influenced by it.[^ss] Sedna, the first found and the one classified as a dwarf planet, ranges from 76.2 to 937 AU in the pair and takes about 11,400 years per orbit; the current JPL solution the explorer draws puts its aphelion at 1,011 AU.[^ss][^sbdb] 2012 VP113 and Leleakuhonua are the other two sednoids drawn, the latter reaching past 2,600 AU.[^sbdb] Some astronomers read the similar tilts of these orbits as the pull of an unseen planet, Planet Nine; others credit observational bias.[^ss] Planet Nine is not drawn. Only the logarithmic map makes this section drawable at all: in it, Sedna's orbit fits on the same screen as Mercury's. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=etno&embed=1" data-title="Extreme trans-Neptunian objects in the Solar System explorer"></div> *Try: set the speed to 100 years/s and watch Sedna barely move while Neptune circles; switch the scale to true and see the planets collapse to a dot.* Connects to: [[#Comparison with extrasolar systems|Comparison with extrasolar systems]] · [[#Scattered disc|Scattered disc]] · [[#Oort cloud|Oort cloud]] ### Oort cloud  *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=hills&embed=1" data-title="The Hills cloud in the Solar System explorer"></div>  *Main article: [[Oort_cloud]] · See also: [[Hills_cloud]], [[Hill_sphere]]* The Oort cloud is a theorized spherical shell of up to a trillion icy bodies, thought to be the source of all long-period comets.[^ss] It is thought to reach from about 2,000 AU to as far as 200,000 AU, with most of its mass between 3,000 and 100,000 AU, though lower estimates put its outer edge no farther than 50,000 AU.[^ss] Its members move slowly and can be nudged sunward by a passing star or the tide of the galaxy, and no present instrument can image it; Voyager 1, the nearest probe, will reach it in about 300 years.[^ss] The cloud extends to the edge of the Sun's [[Hill_sphere|Hill sphere]], 178,000 to 227,000 AU out, where the Sun's gravity gives way to the galaxy's.[^ss] The explorer draws a sampled shell to 100,000 AU, labelled theoretical and illustrative, the flattened inner Hills cloud from about 3,000 to 20,000 AU, and a faint sphere at the Hill-sphere edge.[^hc] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=oort&embed=1" data-title="Oort cloud in the Solar System explorer"></div> *Try: drag around the shell and find the flattened inner Hills cloud; switch the show menu to clouds and boundaries; switch the scale to true and read why true scale cannot show this.* Connects to: [[#Formation and evolution|Formation and evolution]] · [[#Extreme trans-Neptunian objects|Extreme trans-Neptunian objects]] · [[#Comets|Comets]] · [[#Edge of the heliosphere|Edge of the heliosphere]] ## Part VI — Gravitationally unstable populations Meteoroids, dust and comets: the bodies that do not keep their orbits for long, and the trails they leave. ### Meteoroids, meteors and dust *Main article: [[Meteoroid]] · See also: [[Interplanetary_dust_cloud]], [[Zodiacal_light]], [[Meteor_shower]]* Solid bodies between about 30 micrometres and 1 metre are meteoroids; smaller grains are dust.[^ss] Some meteoroids come from broken comets and asteroids, and a few are debris thrown off planets by impacts; most are silicates, nickel and iron.[^ss] A comet sheds a trail of meteoroids along its orbit, and when Earth crosses that trail they burn up as meteors that seem to radiate from one point in the sky, a [[Meteor_shower|meteor shower]].[^ss] Encke's Comet feeds the Southern Taurids of early November, and Halley's Comet the Orionids.[^ms] The inner Solar System is also filled with a zodiacal dust cloud, faintly visible as zodiacal light on dark nights.[^ss] The explorer draws that dust as a thin lens in the ecliptic inside the belt and a stream of debris along Encke's real orbit; both are illustrative samples on real ranges.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=dust&embed=1" data-title="Meteoroids, meteors and dust in the Solar System explorer"></div> *Try: set the year to 2026.83, early November, and the speed to 1 day/s to find Earth near the Encke stream; drag to an edge-on view of the zodiacal lens.* Connects to: [[#Asteroid belt|Asteroid belt]] · [[#Comets|Comets]] ### Comets  *Microsims from the articles this section links:* <div class="wt-simrow"> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Halley&embed=1" data-title="Halley's Comet in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Borisov&embed=1" data-title="2I/Borisov in the Solar System explorer"></div> <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Oumuamua&embed=1" data-title="1I/ʻOumuamua in the Solar System explorer"></div> </div>  *Main article: [[Comet]] · See also: [[Halley's_Comet]], [[Interstellar_object]], [[1I/ʻOumuamua]]* Comets are small icy bodies, usually a few kilometres across, on highly eccentric orbits that bring them inside the planets' orbits and carry them far past Pluto.[^ss] Near the Sun their ice sublimates into a coma and a tail.[^ss] Short-period comets take less than two hundred years per orbit and are thought to come from the Kuiper belt; long-period comets such as Hale-Bopp take thousands of years and come from the Oort cloud.[^ss] [[Halley's_Comet]] last passed in 1986 and returns in mid-2061, on an orbit inclined 162 degrees, so it travels backwards.[^hal][^sbdb] Encke's Comet takes 3.3 years and never reaches Jupiter's orbit.[^sbdb] Two interstellar visitors came through on open hyperbolic paths, 1I/'Oumuamua in 2017 and 2I/Borisov in 2019.[^iso] The explorer draws all five on their JPL orbits, noting that two-body positions far from each epoch are approximate.[^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=comets&embed=1" data-title="Comets in the Solar System explorer"></div> *Try: set the year to 1986 and watch Halley swing past the Sun, then to 2061; set the speed to 1 year/s and watch the two interstellar objects leave and never return.* Connects to: [[#Orbits|Orbits]] · [[#Trojans, Hildas and near-Earth objects|Trojans, Hildas and near-Earth objects]] · [[#Centaurs|Centaurs]] · [[#Scattered disc|Scattered disc]] · [[#Oort cloud|Oort cloud]] · [[#Meteoroids, meteors and dust|Meteoroids, meteors and dust]] ## Part VII — The edge and the neighborhood Where the Sun's wind and then its gravity give way, what lies just beyond, where the Solar System sits in the galaxy, and how people found all this out. ### Edge of the heliosphere *Main article: [[Heliosphere]] · See also: [[Heliopause]], [[Solar_wind]], [[Voyager_1]]* The heliosphere is the bubble the solar wind blows into the interstellar medium.[^ss] Its inner boundary is the termination shock, where the wind slows abruptly, roughly 80 to 100 AU from the Sun upwind and about 200 AU downwind; Voyager 1 passed it in December 2004 at 94 AU.[^ss][^hs] Beyond lies the heliosheath and then the heliopause, where interstellar space begins; Voyager 1 crossed it in August 2012 at 121 AU.[^v1] Beyond the heliopause, at around 230 AU, lies the bow shock, the wake the Sun leaves as it moves through the galaxy.[^ss] The heliosheath may trail like a comet's tail for thousands of AU downwind, so the true shape is not a sphere.[^ss] The explorer draws the three boundaries as translucent spheres at their measured or quoted radii, marked illustrative in shape; the [[Heliopause]] itself is where Voyager 1 left the Sun's wind.[^v1] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=heliosphere&embed=1" data-title="Edge of the heliosphere in the Solar System explorer"></div> *Try: drag outside the shells and look back at the planets; switch the show menu to clouds and boundaries; read the three radii in the readout.* Connects to: [[#Distances and scales|Distances and scales]] · [[#Sun|Sun]] · [[#Oort cloud|Oort cloud]] · [[#Celestial neighborhood|Celestial neighborhood]] · [[#Discovery and exploration|Discovery and exploration]] ### Celestial neighborhood  *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/Interstellar_medium.html" data-title="Interstellar medium"></div>  *Main article: [[Local_Interstellar_Cloud]] · See also: [[Local_Bubble]], [[Alpha_Centauri]], [[Interstellar_medium]]* Within ten light-years of the Sun there are few stars.[^ss] The closest is Proxima Centauri, a small red dwarf 4.25 light-years away, about 269,000 AU, which orbits the Sun-like pair Alpha Centauri A and B.[^ss][^wts] Around the Solar System lies the [[Local_Interstellar_Cloud|Local Interstellar Cloud]], about 30 light-years across; whether the Sun sits just inside it or just outside is not settled.[^lic][^ss] That cloud and several others lie within the Local Bubble, a cavity of hot plasma roughly 300 light-years across, probably blown by recent supernovae.[^ss] This state continues the logarithmic ladder outward from Neptune: the heliopause at 121 AU, Sedna's aphelion, the inner edge of the Oort cloud, the edge of the Hill sphere and finally Proxima Centauri, all on one axis, so the whole Solar System and its nearest neighbour fit on a single ruler.[^v1][^sbdb] <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=neighborhood&embed=1" data-title="The neighborhood in the Solar System explorer"></div> *Try: read each rung of the ruler from Neptune outward; drag to look along the ruler from the Sun; press l to hide the body labels and keep the rungs.* Connects to: [[#Distances and scales|Distances and scales]] · [[#Edge of the heliosphere|Edge of the heliosphere]] · [[#Galactic position|Galactic position]] ### Galactic position *Main article: [[Orion_Arm]] · See also: [[Milky_Way]], [[Galactic_year]]* The Solar System lies in the Milky Way, a barred spiral about 100,000 light-years across with more than 100 billion stars.[^ss] The Sun sits in one of the outer arms, the [[Orion_Arm|Orion Arm]], also called the Local Spur, a structure some 3,500 light-years wide and about 20,000 light-years long.[^ss][^orion] It is a member of the thin disk, orbiting close to the galactic plane at about 220 kilometres per second, and completes one circuit, a galactic year, in about 240 million years.[^ss] The Sun's path through space heads toward the constellation Hercules, near the bright star Vega, and the plane of the ecliptic lies about 60 degrees from the plane of the galaxy.[^ss] The galactic centre lies 24,000 to 28,000 light-years away.[^ss] This section has no state of its own; the neighborhood ladder is as far out as the explorer draws. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=neighborhood&embed=1" data-title="The neighborhood in the Solar System explorer"></div> *Try: open the neighborhood state and follow the ruler to Proxima Centauri, the last rung before the galaxy takes over.* Connects to: [[#Celestial neighborhood|Celestial neighborhood]] ### Discovery and exploration *Main article: [[Discovery_and_exploration_of_the_Solar_System]] · See also: [[Timeline_of_Solar_System_exploration]], [[Voyager_1]]* Knowledge of the Solar System grew slowly. Aristarchus of Samos proposed a Sun-centred cosmos in antiquity, but until the Renaissance most astronomers held Earth still at the centre.[^ss] Nicolaus Copernicus built the first mathematically predictive heliocentric system, and Johannes Kepler, using Tycho Brahe's observations and elliptical orbits, produced tables accurate enough for Pierre Gassendi to predict a transit of Mercury in 1631.[^ss] Galileo and Simon Marius found Jupiter's four large moons with early telescopes.[^ss] The explorer's own ephemeris descends from that line: Keplerian ellipses, now fitted by JPL to modern observations.[^jpl] Exploration by spacecraft carried the record outward; [[Voyager_1|Voyager 1]], launched in 1977, crossed the termination shock at 94 AU and the heliopause at 121 AU, and those crossing radii are the exploration facts this state carries.[^v1][^hs] Probe trajectories are not yet drawn. <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=heliosphere&embed=1" data-title="Discovery and exploration in the Solar System explorer"></div> *Try: open the heliosphere state and read the two Voyager crossing radii; set the year to 1800 and play forward to see the sky Copernicus and Kepler described.* Connects to: [[#Edge of the heliosphere|Edge of the heliosphere]] ## Spine | # | Section | Main article | See also | State | Status | |---|---|---|---|---|---| | 1 | Definition | [[IAU_definition_of_planet]] | [[Dwarf_planet]], [[Small_Solar_System_body]], [[Clearing_the_neighbourhood]] | `?view=census` | live · articles drafted · solar/Solar_System.html?view=census&embed=1 | | 2 | Formation and evolution | [[Formation_and_evolution_of_the_Solar_System]] | [[Protoplanetary_disk]], [[Nice_model]], [[Grand_tack_hypothesis]], [[Late_Heavy_Bombardment]] | `?view=composition` | live · articles drafted · solar/Solar_System.html?view=composition&embed=1 | | 3 | Composition | [[Frost_line_(astrophysics)]] | [[Terrestrial_planet]], [[Gas_giant]], [[Ice_giant]] | `?view=composition` | live · articles drafted · solar/Solar_System.html?view=composition&embed=1 | | 4 | Orbits | [[Orbit]] | [[Kepler's_laws_of_planetary_motion]], [[Ecliptic]] | `?view=orbits` | live · articles drafted · solar/Solar_System.html?view=orbits&embed=1 | | 5 | Distances and scales | [[Astronomical_unit]] | [[Solar_System_model]] | `?view=scale` | live · articles drafted · solar/Solar_System.html?view=scale&embed=1 | | 6 | Habitability | [[Habitable_zone]] | [[Earth]], [[Solar_wind]] | `?view=zones` | live · articles drafted · solar/Solar_System.html?view=zones&embed=1 | | 7 | Comparison with extrasolar systems | [[Planetary_system]] | [[Planet_Nine]] | `?view=orbits` | live · articles drafted · solar/Solar_System.html?view=orbits&embed=1 | | 8 | Sun | [[Sun]] | [[Solar_wind]], [[Heliosphere]] | `?obj=Sun` | live · articles drafted · solar/Solar_System.html?obj=Sun&embed=1 | | 9 | Mercury | [[Mercury_(planet)]] | — | `?obj=Mercury` | live · articles drafted · solar/Solar_System.html?obj=Mercury&embed=1 | | 10 | Venus | [[Venus]] | — | `?obj=Venus` | live · articles drafted · solar/Solar_System.html?obj=Venus&embed=1 | | 11 | Earth and the Moon | [[Earth]] | [[Moon]] | `?obj=Earth` | live · articles drafted · solar/Solar_System.html?obj=Earth&embed=1 | | 12 | Mars | [[Mars]] | [[Moons_of_Mars]] | `?obj=Mars` | live · articles drafted · solar/Solar_System.html?obj=Mars&embed=1 | | 13 | Asteroid belt | [[Asteroid_belt]] | [[Ceres_(dwarf_planet)]], [[4_Vesta]], [[2_Pallas]], [[10_Hygiea]], [[Kirkwood_gap]] | `?obj=belt` | live · articles drafted · solar/Solar_System.html?obj=belt&embed=1 | | 14 | Trojans, Hildas and near-Earth objects | [[Asteroid]] | [[Jupiter_trojan]], [[Hilda_asteroid]], [[Near-Earth_object]] | `?obj=trojans` | live · articles drafted · solar/Solar_System.html?obj=trojans&embed=1 | | 15 | Jupiter | [[Jupiter]] | [[Galilean_moons]], [[Io_(moon)]], [[Europa_(moon)]], [[Ganymede_(moon)]], [[Callisto_(moon)]] | `?obj=Jupiter` | live · articles drafted · solar/Solar_System.html?obj=Jupiter&embed=1 | | 16 | Saturn | [[Saturn]] | [[Rings_of_Saturn]], [[Titan_(moon)]], [[Enceladus]] | `?obj=Saturn` | live · articles drafted · solar/Solar_System.html?obj=Saturn&embed=1 | | 17 | Uranus | [[Uranus]] | — | `?obj=Uranus` | live · articles drafted · solar/Solar_System.html?obj=Uranus&embed=1 | | 18 | Neptune | [[Neptune]] | [[Triton_(moon)]] | `?obj=Neptune` | live · articles drafted · solar/Solar_System.html?obj=Neptune&embed=1 | | 19 | Centaurs | [[Centaur_(small_Solar_System_body)]] | — | `?obj=centaurs` | live · articles drafted · solar/Solar_System.html?obj=centaurs&embed=1 | | 20 | Kuiper belt | [[Kuiper_belt]] | [[Trans-Neptunian_object]], [[Classical_Kuiper_belt_object]], [[Plutino]], [[Resonant_trans-Neptunian_object]] | `?obj=kuiper` | live · articles drafted · solar/Solar_System.html?obj=kuiper&embed=1 | | 21 | Pluto and the dwarf planets of the belt | [[Pluto]] | [[Charon_(moon)]], [[Haumea]], [[Makemake]], [[Orcus_(dwarf_planet)]], [[Quaoar]] | `?obj=Pluto` | live · articles drafted · solar/Solar_System.html?obj=Pluto&embed=1 | | 22 | Scattered disc | [[Scattered_disc]] | [[Eris_(dwarf_planet)]], [[Gonggong_(dwarf_planet)]] | `?obj=scattered` | live · articles drafted · solar/Solar_System.html?obj=scattered&embed=1 | | 23 | Extreme trans-Neptunian objects | [[Extreme_trans-Neptunian_object]] | [[Sedna_(dwarf_planet)]], [[Sednoid]], [[Detached_object]], [[Planet_Nine]] | `?obj=etno` | live · articles drafted · solar/Solar_System.html?obj=etno&embed=1 | | 24 | Oort cloud | [[Oort_cloud]] | [[Hills_cloud]], [[Hill_sphere]] | `?obj=oort` | live · articles drafted · solar/Solar_System.html?obj=oort&embed=1 | | 25 | Meteoroids, meteors and dust | [[Meteoroid]] | [[Interplanetary_dust_cloud]], [[Zodiacal_light]], [[Meteor_shower]] | `?obj=dust` | live · articles drafted · solar/Solar_System.html?obj=dust&embed=1 | | 26 | Comets | [[Comet]] | [[Halley's_Comet]], [[Interstellar_object]], [[1I/ʻOumuamua]] | `?obj=comets` | live · articles drafted · solar/Solar_System.html?obj=comets&embed=1 | | 27 | Edge of the heliosphere | [[Heliosphere]] | [[Heliopause]], [[Solar_wind]], [[Voyager_1]] | `?obj=heliosphere` | live · articles drafted · solar/Solar_System.html?obj=heliosphere&embed=1 | | 28 | Celestial neighborhood | [[Local_Interstellar_Cloud]] | [[Local_Bubble]], [[Alpha_Centauri]], [[Interstellar_medium]] | `?view=neighborhood` | live · articles drafted · solar/Solar_System.html?view=neighborhood&embed=1 | | 29 | Galactic position | [[Orion_Arm]] | [[Milky_Way]], [[Galactic_year]] | `?view=neighborhood` | live · articles drafted · solar/Solar_System.html?view=neighborhood&embed=1 | | 30 | Discovery and exploration | [[Discovery_and_exploration_of_the_Solar_System]] | [[Timeline_of_Solar_System_exploration]], [[Voyager_1]] | `?obj=heliosphere` | live · articles drafted · solar/Solar_System.html?obj=heliosphere&embed=1 | ## The book shelf | # | Title | Where it serves this page | OTL record | |---|---|---|---| | 1 | University Physics I: Classical Mechanics (Gea-Banacloche, 2019) | gravitation and Kepler's laws: sections 4-5, 7 | [open.umn.edu](https://open.umn.edu/opentextbooks/textbooks/university-physics-i-classical-mechanics) | | 2 | University Physics Volume 1 (OpenStax, 2016) | gravitation, orbits and Kepler's laws: sections 4, 5, 21 | [open.umn.edu](https://open.umn.edu/opentextbooks/textbooks/university-physics-volume-1) | | 3 | Mechanics and Relativity (Idema, 2018) | central forces and orbits: sections 4, 12, 23 | [open.umn.edu](https://open.umn.edu/opentextbooks/textbooks/mechanics-and-relativity) | | 4 | Variational Principles in Classical Mechanics, revised second edition (Cline, 2018) | the two-body problem behind every orbit the explorer draws: section 4 | [open.umn.edu](https://open.umn.edu/opentextbooks/textbooks/variational-principles-in-classical-mechanics) | | 5 | Space Systems: Emerging Technologies and Operations (2022) | spacecraft and missions: sections 27, 30 | [open.umn.edu](https://open.umn.edu/opentextbooks/textbooks/space-systems-emerging-technologies-and-operations) | All five are in `Portal Books/Portal_Books_Manifest.csv` as downloaded Open Textbook Library titles (openly licensed through the OTL record linked). The agency sources sit beside the shelf rather than on it: JPL Solar System Dynamics (approximate planet positions, Table 1; the Small-Body Database) and the NASA NSSDCA Planetary Fact Sheet, both fetched on 2026-09-18 and cited in the notes below. ## Crosslinks - Anchor article: [[Solar_System]] (revision 1372787813, the pair whose outline this page follows). - Sibling rooms: [[PORTAL_Physics]] for gravitation and orbital mechanics, [[PORTAL_Chemistry]] for composition, [[PORTAL_Energy]] for the Sun as a power source. - The explorer: one page, `solar/Solar_System.html` on the Wikitube three.js host, with 59 object and population states and 7 views; its data library is `wt/wt-solar.js`. A child article embeds its own state as `?obj=<id>&embed=1`. - The build queue: [[PORTAL_Solar_System.worklist]] (30 Main and 64 See-also articles). - Index: [[PORTAL_INDEX]] · all rooms: [[portals]]. ## Notes [^ss]: Solar System, English Wikipedia, revision 1372787813 (read 2026-09-18) - the pair; section and infobox figures. [^fs]: NASA NSSDCA, Planetary Fact Sheet, https://nssdc.gsfc.nasa.gov/planetary/factsheet/ (fetched 2026-09-18). [^jpl]: JPL Solar System Dynamics, Approximate Positions of the Planets, Table 1 (Keplerian elements and rates, J2000 ecliptic, valid 1800-2050), https://ssd.jpl.nasa.gov/planets/approx_pos.html (fetched 2026-09-18). The explorer's test places Earth and Mars 0.08 degrees apart in heliocentric longitude on 2003-08-28. [^sbdb]: JPL Small-Body Database API, osculating elements at each body's epoch, fetched 2026-09-18 (_registry/plans/solar_system_sbdb_2026-09-18.json); positions propagated two-body. [^wts]: Computed in wt-solar.js from the cited inputs: light-time = distance x 499.005 s per AU (IAU 2012 AU, c = 299,792.458 km/s); Proxima Centauri 4.25 ly x 63,241.08 AU/ly; solar radius 695,700 km (IAU 2015 nominal). [^sun]: Sun, English Wikipedia, revision 1375342983 (infobox: obliquity 7.25 degrees to the ecliptic). [^iau]: IAU definition of planet, English Wikipedia, revision 1372697874. [^fl]: Frost line (astrophysics), English Wikipedia, revision 1372525572 (about 2.7 AU when planetesimals formed; 170 K at 2.7 AU, Hayashi 1981). [^hz]: Habitable zone, English Wikipedia, revision 1374517544 (estimates table: Kasting et al. 1993, 0.95-1.37 AU; Kopparapu et al. 2013, 0.99-1.67 AU). [^au]: Astronomical unit, English Wikipedia, revision 1372862298 (IAU 2012: 149,597,870,700 m). [^mo]: Moon, English Wikipedia, revision 1375536085 (infobox). [^mm]: Moons of Mars, English Wikipedia, revision 1369832505 (table). [^kg]: Kirkwood gap, English Wikipedia, revision 1372351484. [^jt]: Jupiter trojan, English Wikipedia, revision 1372350183. [^io]: Io (moon), English Wikipedia, revision 1375514130 (infobox). [^eu]: Europa (moon), English Wikipedia, revision 1374725737 (infobox). [^ga]: Ganymede (moon), English Wikipedia, revision 1375329281 (infobox). [^ca]: Callisto (moon), English Wikipedia, revision 1372366198 (infobox). [^rs]: Rings of Saturn, English Wikipedia, revision 1375287904 (ring table: C Ring 74,658-92,000 km; A Ring 122,170-136,775 km; F Ring 140,180 km). [^ti]: Titan (moon), English Wikipedia, revision 1374767643 (infobox). [^en]: Enceladus, English Wikipedia, revision 1372997315 (infobox). [^tr]: Triton (moon), English Wikipedia, revision 1375101176 (infobox). [^ch]: Charon (moon), English Wikipedia, revision 1374241186 (infobox: 19,595.764 km planetocentric, 17,181 km barycentric). [^kb]: Kuiper belt, English Wikipedia, revision 1372106056. [^hc]: Hills cloud, English Wikipedia, revision 1370779979. [^ms]: Meteor shower, English Wikipedia, revision 1370783611 (table of showers and parent bodies). [^hal]: Halley's Comet, English Wikipedia, revision 1375206184. [^iso]: Interstellar object, English Wikipedia, revision 1373958509. [^hs]: Heliosphere, English Wikipedia, revision 1372549208. [^v1]: Voyager 1, English Wikipedia, revision 1373967480 (mission timeline: termination shock 2004-12-17 at 94 AU; heliopause 2012-08-25 at 121 AU). [^lic]: Local Interstellar Cloud, English Wikipedia, revision 1336856340. [^orion]: Orion Arm, English Wikipedia, revision 1357759388. **Spine notes** (from `_registry/plans/SOLAR_SYSTEM_SECTIONS.md`). The part and section order follows the H2/H3 outline of the pair at revision 1372787813 with two adjustments: each planet gets its own section, and the pair's asteroid material is split into the main belt (13) and the other asteroid populations (14); the Hill sphere stays with the Oort cloud (24). `mnemonic_hub` is MTN's to change. **Where the sources disagree** (both readings kept, the drawn one named). The frost line: the pair puts it at roughly five times Earth's distance, the Frost line article at about 2.7 AU when planetesimals formed; the explorer draws 2.7 AU. Sedna's aphelion: the pair gives 937 AU, the current JPL solution 1,011 AU; the explorer draws the JPL orbit. Moon counts: the pair counts 115 moons for Jupiter, 293 for Saturn and 29 for Uranus; the NASA fact sheet as fetched lists 95, 274 and 28; this page quotes the pair. The Hill sphere: the pair's Oort cloud section gives 178,000 to 227,000 AU and its boundary section up to 230,000 AU; the explorer draws 200,000 AU. The habitable zone: the explorer draws Kopparapu et al. (2013), 0.99 to 1.67 AU, the range that agrees with the pair's statement that Earth and Mars orbit inside it. **Illustrative, and said on screen.** The sampled points of every belt and cloud (their ranges are real, each point is a seeded random sample); body sizes in log mode (a size law); the spherical shells for the heliosphere boundaries (real radii, simplified shape); the moons' starting phases in the local frames; the azimuth of each planet's pole line (the tilt is real). *Created 2026-09-18 · wt-portal run · 30 sections · 1 explorer · 0 deletions* --- *Repopulated 2026-09-19 · append-only · source: _tools/generate/g34_portal_section_sims.py@00a28cb2 (players of the linked articles, each URL 200-checked) · 128 added · 0 deletions*