Sun, planets, asteroids, moons, and comets {solar system}| formed 4,600,000,000 years ago. Solar system has 10^13 meter diameter, has mass 10^36 grams, and will last 10^16 seconds.
space between planets
Space between planets has 10 ions per cubic centimeter.
space erosion
Space objects erode by 0.001 meters every 10^6 years.
Pioneer spacecraft
Pioneer 10 and Pioneer 11 spacecraft photographed Jupiter and Saturn [1972 to 1973] and are now outside solar system. At 10 astronomical units, they slowed from projected speed {Pioneer anomaly}. Researchers do not yet know slowdown direction. If it is toward Sun, it indicates something new about gravity. If it is toward Earth, it indicates something about light velocity. If it is along motion direction, it indicates something about inertia or drag. If it is along spin axis, it indicates something about Pioneer spacecraft.
Moons {satellite}| can be close to planets in circular orbits near ecliptic {regular moon} or far from planets in elliptical orbits out of ecliptic {irregular moon}. Regular moons formed from planetary dust cloud. Irregular moons formed in Kuiper belt or as asteroids. Planet can capture irregular moon when two nearby potential moons interact to slow one down. Planet gravitation must be more than Sun gravitation in that region {Hill sphere}. Orbit shape and tilt relate {Kozai resonance}. Triton is largest irregular moon. Small moons can form from large-moon breakup.
Gravitational forces {tidal torque} cause planet and moon water and land movements (tide). Friction causes tides to be slower than gravitational forces. Sun tidal torque affects Mercury and Venus spin. Jupiter and Saturn tidal torques affect inner-moon spins.
Mars has magnesium and iron silicates, iron-sulfur rocks {troilite}, and free iron.
Earth-axis tilt causes a day {autumnal equinox}| with equal daylight and dark in autumn.
Earth-axis tilt causes a longest-daylight day {summer solstice}|.
Earth-axis tilt causes a day {vernal equinox}| with equal daylight and dark in spring.
Earth-axis tilt causes a shortest-daylight day {winter solstice}|.
Solar system has objects {comet}| that start outside Pluto orbit. Famous comet is Halley's comet, which neared Sun in 1986 and has 76-year orbit.
composition
Comets have frozen water, iron, silicate, carbon, and nickel, plus ammonia, carbon dioxide, methane, cyanogen, and hydrogen cyanide.
parts
Comets have central ball {nucleus, comet} and coma.
size
Comets have average diameter 2000 meters.
number
More than 1,000,000,000,000 comets exist, with total mass 1 to 1000 times Earth mass.
orbit
Comets have elliptical orbits, averaging 10,000 years, in same motion direction as planets, extending up to 1/5 distance to nearest star. Comet orbits change as they come close to Sun, because hot side evaporates more than cold side and spin interacts with Sun gravity.
tail
As comets approach Sun and evaporate, they leave curved dust tails along motion path. As comets approach Sun, solar wind creates straight ion tails, away from Sun.
meteor showers
Comet dust causes meteor showers, which happen 600 times a year. Meteor-shower names are the name of the constellation in which they appear: Quadrantids in January, Lyrids in April, Aquarids in May, Perseids in August, Draconids in October, Orionids in October, Taurids in November, and Geminids in December.
Comets have a central nucleus surrounded by a dust and gas cloud {coma, comet}.
Most comets lie in circular orbits {Oort cloud}| beyond Pluto, where they formed. From there, passing star can push them into elliptical orbit. Some comets lie in Kuiper belt.
Comet debris causes faint patch {counterglow} {gegenschein}|, 10 degrees diameter, in night sky in direction opposite Sun.
Comet debris causes faint glow {zodiacal light}| along ecliptic, which is 10 degrees above horizon, in eastern sky before sunrise or in western sky after sunset.
Moon enters Earth shadow {lunar eclipse}| 0 to 3 times a year.
Moon passes in front of Sun {solar eclipse}| 2 to 5 times a year.
A satellite {Moon} orbits Earth.
properties
Diameter is 2,000,000 meters. Mass is 1/80 of Earth mass. Surface area equals Africa area. Density is 2/3 of Earth density. Gravity is 1/5 of Earth gravity.
orbit
Orbit tilts at 5-degree incline to Earth orbit. Moon is 376,000,000 meters from Earth. Gravitational effect of Earth spin moves Moon slowly away from Earth. 4,000,000,000 years ago, Moon was 100,000,000 meters from Earth.
rotation
Moon rotates every 27.3 days, keeping same side toward Earth, ever since 10^9 years ago.
temperature
Surface temperature is 200 C by day and -150 C at night.
atmosphere
Moon has thin atmosphere with no water.
layers
Core has radius 400 miles and is molten. Peridotite and dunite lie from 400 miles from center to 40 miles below surface. Peridotite and dunite are oxide rocks like those in Earth mantle. Basalt layer lies from 40 to 15 miles deep. Crust is anorthositic rock 60,000 meters thick, with some granite.
surface
Surface has basalt rock from volcanoes that erupted more than 3,000,000,000 years ago, making mountains 8000 meters high. Mare basalt, from partial interior melting, is in plains {maria}. Another basalt type has anorthositic rock and KREEP norite from mountain {highland} partial melting. KREEP norite has potassium, rare earths, and phosphorus.
craters
Most craters are more than 4,000,000,000 years old. Largest crater is 250,000-meter diameter and 1000 meters high. Craters are 10 to 20 times bigger than their meteors.
history
Moon began when Mars-sized body collided with Earth and splashed material into orbit. It is much less likely that it began from smaller bodies in orbit around Earth or by capture. Orbiting material gravitated together and melted surface. Lighter molecules rose to surface and cooled to become crust. Later, before 4.2 x 10^9 years ago, meteorites pressed highland rocks together to make breccia. Then crust formed again. Then KREEP norite formed around Mare Imbrium. Then large impacts 4 x 10^9 years ago made maria basins. Then volcanoes erupted for 0.7 x 10^9 to 1.0 x 10^9 years, filling maria with lava. Finally, Moon cooled.
features
Tycho crater is at low center. Copernicus crater is at left center. Archimedes crater is at low center. Ptolemaeus crater is at center. Carpathian Mountains are around Copernicus. Mare Imbrium plain or Sea of Rains is at left and up. Mare Serenitatis or Sea of Serenity is at right and up. Mare Tranquillitatis or Sea of Tranquillity is at right center. Oceanus Procellarum is at left center. South Pole is in Aitken Basin on far side.
phases
Moon has phases. New moon is thin crescent. Crescent moon is fuller. First-quarter moon has light on left half, with Sea of Tranquility and Pyrenees Mountains. Gibbous moon is between first quarter and full. Full moon is a circle. Gibbous moon is between third quarter and full. Third-quarter moon has light on right half, with Sea of Shadows and Carpathian Mountains. Crescent moon is less. New moon is thin crescent.
Moon parts not in direct sunlight can reflect light that first bounced off Earth {earthshine}.
Moonlight refraction by thin, high, icy clouds causes white, 22-degree ring {lunar halo} {aureole, Moon}, and sometimes 46-degree ring, around Moon.
Dense masses {mascon} under lunar maria are buried asteroids or heavy lava.
By star positions, Moon orbit is 27.3 days {sidereal month} and tilts at 5-degree incline to Earth orbit.
Time between new moons is 29-1/2 days {lunar month} {synodic month}.
Basalt can have plagioclase feldspar formed by crystal fractionation {anorthositic rock} and KREEP norite from partial mountain/highland melting. KREEP norite has potassium, phosphorus, and rare earths.
Meteor collisions vaporize and fuse iron and silicon {hapkeite}.
Basalt {mare basalt}, from partial interior melting, can be in maria.
Planets orbit the Sun {orbit, planet}| {planetary orbit}.
Planets and asteroid belt lie at 4, 7, 10, 16, 28, 52, 100, 196, 388, and 772 units from Sun {Bode's law} {Bode law}.
Planets can be in line with Sun and Earth {conjunction, planet}|, on far side of Sun {inferior conjunction} or on same side as Earth {superior conjunction}.
planet-orbit plane {ecliptic}|.
Seen from Earth, Venus or Mercury has distance {elongation} from Sun.
Bodies can pass in front of other bodies {occultation}|.
Seen from Earth, planets and their moons periodically appear to move backward {retrograde motion}.
Mercury and Venus can pass in front of Sun {transit}|.
In ancient theories of Earth-centered universe, orbits were circles and circles of circles {epicycle} {epicycle construction} {eccentric construction}.
Perhaps, Earth is near solar-system center {geocentric system}.
Sun is near solar-system center {heliocentric system}.
Earth axis points slightly more counterclockwise, looking north, each year {precession of the equinoxes}| {equinox precession} and completes circle in 22,000 to 26,000 years. Moon nutation orbital-plane changes cause precession rate to vary over an 18.6-year cycle. Orbit variations also have 41,000-year and 100,000-year cycles.
Moon orbital-plane changes cause precession rate to vary over an 18.6-year cycle {nutation, Earth orbit}|.
Orbit around Earth has point {apogee} farthest from Earth.
Orbit around Earth has point {perigee} nearest Earth.
Orbit around Sun has point {aphelion} farthest from Sun.
Orbit around Sun has point {perihelion} nearest Sun.
At vernal equinox, Sun is at a celestial-sphere point {first point of Aries}.
For two objects in space, five points {Lagrangian point} {libration point} have equal competing gravities. Three are unstable, but two are stable.
Planets {planet} are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, and Uranus.
planet formation
Planets form after star forms. 20% of stars have planets. Multiple stars probably do not have planets.
planet formation: materials
Iron, silicates, magnesium, aluminum, and calcium oxides are 0.5% of dust-and-gas-cloud mass and are solid at planetary-cloud temperatures and pressures. Water, methane, and ammonia are 1.5% of dust-and-gas-cloud mass and freeze at temperature -120 C at pressures in dust-and-gas cloud. Hydrogen and helium are 98% of dust-and-gas-cloud mass and are gases at planetary-cloud temperatures and pressures.
planet formation: temperature
Dust-and-gas-cloud temperatures stay constant at each distance from star during planet formation. Planetary-cloud inner region is 3 x 10^9 meters from star, at temperature 1600 K. Water is liquid 1.3 x 10^11 meters from star, because temperature is less than 100 C and more than 0 C.
planet formation: process
When stars form, dust-and-gas clouds become disks. Disks are thickest at 1.5 x 10^12 meters from center.
Disc contraction leaves behind flat ring 10^9 to 10^12 meters thick, with temperature from 1800 C to -250 C, total mass equal to new star mass, and dust particles 10^-6 meters diameter.
Dust particles stick together to make one-micron-diameter chunks. Making micron-size particles takes 100,000 years. Dust particles stick together beyond distance where temperature is less than 1800 K. Small grains flow with gas.
Millimeter-size dust hits gas and slows. At distance at which water freezes {snow line}, dust does not slow, because water evaporates inside that distance and gas is faster than dust grains. Orbits are elliptical.
Dust particles larger than millimeter diameter fall toward planet and cannot stay in orbit, because gas orbits slower than them, they hit gas, and slow.
Over one million years, kilometer-size planetesimals form, removing all dust.
For 100,000 years, inside distance where water freezes, planetesimals collide to make planets one-tenth Earth mass. For one to ten million years, outside distance where water freezes, planetesimals collide to make planets four times Earth mass. Interactions make spherical orbits.
planet formation: large planets
Ten-times-Earth-mass bodies, just outside distance where water freezes, can attract gas that cools by heat transfer through translucent gas. Large planets cause waves in gas that slow planet. Gas giant planets do not form if they spiral in too fast or stay too hot. Making large planets typically requires heavy elements and medium-to-large stars. It also requires that gas does not deplete too fast.
Planets like Earth are too small to attract hydrogen gas. Planets like Uranus and Neptune are just big enough to collect gases heavier than hydrogen. Planets like Jupiter can attract all gases, no matter what temperature.
planet formation: solar wind
After planets form, solar wind and radiation blow away uncondensed dust and gases.
planet formation: gas giant
For several million years, first gas-giant planet disturbs other planetesimals and gas and spirals nearer to star, or stays near original position and more gas giants form beyond it, as matter spirals in and accumulates at border cleared by gas giant.
planet formation: rocky planet
Rocky planets gather material over fifty million years. After rocky planets reach full size, heat from radioactivity melts planet. Layers with different densities form over 10^9 years. Iron is in center, silicates and oxides are near surface, and carbon dioxide, sulfur dioxide, hydrogen sulfide, methane, ammonia, and water vapor are in atmosphere. After layering, cooling forms rocky crust on planet surface.
atmosphere
Atmospheres lose gases by Jeans escape, hydrodynamic escape, polar wind, charge exchange, and solar wind. Water breakdown can lead to hydrogen loss and excess oxygen.
Gaseous planets {chthonian planet} can lose atmosphere and have only rocky core.
Fast charged particles can capture electrons {charge exchange}, become neutral, and escape atmosphere, because magnetic field does not attract them. Earth hydrogen loss is mostly by this process.
Magnetic particles can travel out from poles {polar wind}, along magnetic field lines that do not close. Earth hydrogen loss is partly by this process. Earth helium loss is mostly by this process.
Gaseous planets can lose gas by evaporation from atmosphere top {Jeans escape}. Earth hydrogen loss is partly by this process.
Gaseous planets can lose gas by high heating and upward airflow {hydrodynamic escape}, sweeping all molecule weights along.
Planets {Mercury, planet} can be nearest to Sun.
properties
Diameter is 5,000,000 meters. Mass is 5% Earth mass. Density is slightly less than Earth density. Gravity is one-third Earth gravity.
properties: temperature
Surface temperature is 350 C by day and -170 C at night.
properties: rotation
Mercury rotates every 59 days on axis tilted 28 degrees to ecliptic, because Sun gravity couples spin to orbit.
properties: magnetism
Mercury has tiny magnetic field.
properties: orbit
Mercury is 58,000,000,000 meters from Sun. It has elliptical orbit of 88 days, tilted at 7 degrees to ecliptic.
layers
Mercury has iron core out to 3/4 radius. Mantle has igneous rocks, silicates, iron, and titanium glasses. Thin surface layer has fine, dark silicates. Surface is similar to Moon. It has shallow cliffs greater than 100,000 meters long, caused by crust tightening. It has no large craters. Higher gravity than Moon kept secondary craters near craters, so surface has plains between craters and basins.
atmosphere
Mercury has no atmosphere.
moons
Mercury has no moons.
Planets {Venus, planet} {morning star} {evening star} can be second nearest to Sun.
properties
Diameter is 12,000,000 meters, slightly smaller than Earth diameter. Mass is 88% Earth mass. Density is slightly less than Earth density. Gravity is 85% Earth gravity.
properties: rotation
Venus rotates every 243 days on axis tilted 3 degrees to ecliptic, with direction opposite to all other planets except Uranus.
properties: temperature
Surface temperature is 474 C, because atmosphere traps heat.
properties: magnetism
Venus has no magnetic field.
properties: orbit
Venus is 107,000,000 meters from Sun. Circular orbit takes 243 days and is in ecliptic.
layers
Crust is like Earth crust. Surface has loose granite rocks and many large shallow craters filled by flows from volcanoes.
atmosphere
Thick, layered atmosphere has carbon dioxide at pressure 90 atmospheres, with no oxygen and only water traces. Slow winds are at surface. Fast higher winds blow in spin direction. Lowest clouds are 35,000 meters high and 400 K. Temperature at cloud tops is -33 C. Clouds are 75% sulfuric acid. Because dust in clouds reflects light, only 1% of sunlight reaches surface.
Venus atmosphere is so thick that it refracts light by 90 degrees, so light scattering causes red appearance. Refraction is so great that whole planet surface is visible from any surface point.
moons
Venus has no moons.
Planets {Earth} can be third nearest to Sun.
properties
Diameter is 7917 miles, or 13,000,000 meters, at equator. Circumference is 24902 miles. Diameter at equator is 26.7 miles more than diameter through poles. Density is 5.5 g/cm^3, highest in solar system. Mass is 10^30 grams. Earth will last 10^16 seconds.
properties: orbit
Earth is 149,000,000,000 meters from Sun. One orbit takes 365 1/2 days in a sidereal year. Speed around Sun is 18 miles/second. In Northern Hemisphere, summer is seven days longer than winter, because Earth is closer to Sun then.
properties: rotation
Rotational speed at equator is 0.3 miles/second. Earth turns 15 degrees each hour, as it rotates every 24 hours west to east. Spin slows through tidal interaction with Moon and Sun. 4 x 10^9 years ago, day was 10 hours long. In Cambrian Era, day was 21 hours long. Axis tilts 23.5 degrees from orbit plane.
properties: temperature
Average surface temperature is 22 C. Heat is half from radioactive decay and half from kinetic energy gained from potential-energy loss as matter gathered by gravity at formation.
atmosphere
Air is 10^-6 of Earth weight. Average surface pressure is one atmosphere. Hydrogen-gas halo {geocorona} goes out to 15 radii, emitting ultraviolet light.
moon
Earth has one moon.
Planets {Mars, planet} can be fourth nearest to Sun.
properties
Diameter is 6,800,000 meters. Mass is 12% Earth mass. Density is 4 g/cm^3. Gravity is 38% Earth gravity.
properties: rotation
Mars rotates every 24.5 hours on axis inclined 23 degrees to orbit.
properties: orbit
Mars is 227,000,000,000 meters from Sun. It has slightly elliptic orbit of 1.88 years, slightly inclined to ecliptic.
properties: magnetism
Mars has no magnetic field.
properties: temperature
Surface temperature is 250 K, with high 290 K.
formation
Rapid matter accretion at solar-system beginning melted crust in just 10^5 years. Then iron and iron-sulfur core formed. Crust cooled. Plains and volcanoes formed 3.5 x 10^9 years ago. Crust has no plates or movement. Crust has stretched since forming.
surface
North is low plain with few craters. South is highlands with many craters. Tharsis Plateau is at equator, with very high volcanoes. Volcanoes are over hot spots around equator.
surface: sand
Surface has rocks and red dust. Sandstorms are 300 km/hr. When Mars is farthest from Sun, great dust storm lasts 3 months.
surface: rocks
Mars has magnesium and iron silicates, iron-sulfur rocks (troilite), and free iron. Dark regions have basalt, such as plagioclase and pyroxene. Northern plains are andesite. Hematite is near equator.
surface: water
Surface has phyllosilicate clays and hydrated iron oxides, which indicate water, but no carbonates. Surface has sedimentary rocks with sulfur and hydrates. Sulfur degrades carbonates and inhibits clay formation. Mars dried out and cooled between 3.5 billion years ago and 2.5 billion years ago. Water ice extends deep into surface, except at equator.
surface: ice caps
Polar ice caps are water ice with some carbon-dioxide ice. At maximum, they are 10% of surface. Layered regions near poles show changes.
atmosphere
Mars has thin atmosphere, with surface pressure 0.01 atmosphere. Atmosphere has carbon dioxide, water traces, and no oxygen. Clouds are over volcanoes. Thin clouds are over poles.
landmarks
Nix Olympia or Olympus Mons is 15 miles high and 370 miles across. Mars Rift Valley is 3000 miles long and 1500 miles wide. Coprates is a large river-like system. Hellas crater is a featureless bowl-shaped region. Valles Marineris canyon is north of south highlands. Argyre Basin has 1000 km diameter.
moons
Two small moons are in rapid close orbit. Phobos is larger, and Deimos is smaller.
Planets {Jupiter, planet} can be fifth nearest to Sun and largest planet.
properties
Diameter is 142,000,000 meters. Mass is 318 times Earth mass. Density is 1.33 g/cm^3, because it is 80% hydrogen. Gravity is 2.64 times Earth gravity.
properties: rotation
Jupiter rotates every 10 hours on axis inclined 3 degrees to orbit.
properties: magnetism
Magnetic radiation fields are 10 to 10^5 stronger than Earth fields and make a flat disc 4 x 10^6 miles diameter.
properties: temperature
Surface temperature is 128 K, and surface radiates heat.
properties: orbit
Jupiter is 778,000,000,000 meters from Sun. Circular orbit of 12 years slightly inclines to ecliptic.
layers
Jupiter has a rocky core. Around core is a 46,000,000-meter-diameter metallic ionized liquid-hydrogen layer, at temperature 11,000 K to 30,000 K and pressure 10^7 lb/in^2 or 3 x 10^6 atmosphere. This layer has convection currents that create magnetism and heat flow. 46,000,000 to 70,000,000 meters diameter is liquid hydrogen with 20% helium. Above that layer is a gaseous hydrogen-and-helium layer.
atmosphere
Atmosphere is 1,000,000 meters thick and has layers. First is water drops and ice. Then frozen ammonia is at temperature 110 K. Above that is methane. Gaseous hydrogen is at top. Atmosphere has red and brown belts. Cooler belts are lighter, and hotter belts are darker. Great red spot is swirling gas fed by smaller vortices and is a stable non-linear system. Atmosphere winds are up to 300 km/hr.
moons
Jupiter has 15 moons, four large. Ganymede is size of Mercury. Callisto is smaller than Ganymede and has ice-rock interior. Perhaps, Callisto has water layer. Io has salt, gaseous sodium cloud, and many active volcanoes. Europa is Moon size.
Planets {Saturn, planet} can be sixth nearest to Sun and second-largest planet.
properties
Diameter is 121,000,000 meters. Mass is 95 times Earth mass. Density is 0.7 g/cm^3, because it is 66% hydrogen. Gravity is 1.14 times Earth gravity.
properties: rotation
Saturn rotates every 10 hours on axis tilted 27 degrees to orbit.
properties: temperature
Surface temperature is -170 C.
properties: orbit
Saturn is 1,427,000,000,000 meters from Sun. Circular orbit of 29.5 years slightly inclines to ecliptic.
layers
Core is rock, 20,000,000-meter diameter. Around core is ice 5,000,000 meters thick. Around ice layer is metallic hydrogen 8,000,000 meters thick. Around that layer is molecular hydrogen.
atmosphere
Atmosphere is like Jupiter. Saturn has yellow and green belts. Perhaps, dark particles in atmospheres of Saturn, Titan, and Jupiter are polymers.
moons
Saturn has 10 moons. Titan is largest moon, with diameter 5,000,000 meters. It is the only moon with atmosphere, mainly nitrogen, and has opaque red methane and hydrogen clouds. It has rock core, wet water and ammonia mantle, and ice crust. Surface temperature is -180 C.
Iapetus has surface organic material. Enceladus has diameter 504 kilometers, has rocky core, has icy surface, has liquid water under surface, has tidal forces, makes water jets from south-pole plain that add water to E-ring, and has organic compounds. Other main moons, from inner to outer, are Prometheus, Epimetheus, Pandora, Janus, Mimas, Enceladus, Tethys, Dione, and Rhea.
rings
Rings of ice crystals and ice-coated dust 1-centimeter diameter are from 15,000,000 to 79,000,000 meters. Rings are 0.1 to 16,000 meters thick. Outer E-ring goes from Mimas to between Dione and Rhea.
Planets {Uranus, planet} can be seventh nearest to Sun and third-largest planet.
properties
Diameter is 50,000,000 meters. Mass is 14.5 times Earth mass. Density is 1.6 g/cm^3, because it is 15% hydrogen. Gravity is 1.17 of Earth gravity.
properties: rotation
Uranus rotates every 11 hours on axis almost parallel to orbit plane, 82 degrees to vertical, in opposite direction from Earth direction.
properties: temperature
Surface temperature is 70 K.
properties: orbit
Uranus is 2,860,000,000,000 meters from Sun. Circular orbit of 84 years is in ecliptic.
layers
Rocky core is 16,000,000-meter diameter, at 4000 K and surface pressure 2 x 10^6 atmosphere. Ice layer is 8,000,000 meters thick. Around that layer is molecular hydrogen. Uranus has solid-methane outer layer.
atmosphere
Atmosphere has hydrogen, helium, and methane. Uranus has greenish color.
moons
Uranus has five moons.
Planets {Neptune, planet} can be eighth nearest to Sun and fourth-largest planet [discovered 1846].
properties
Diameter is 45,000,000 meters, four times Earth diameter. Mass is 17 times Earth mass. Density is 2.3 g/cm^3, because it is 25% hydrogen. Gravity is 1.18 of Earth gravity.
properties: rotation
Neptune rotates every 16 to 18 hours on axis tilted 29 degrees to orbit.
properties: magnetism
Neptune has magnetic field.
properties: temperature
Surface temperature is 50 K to 55 K.
Like Jupiter and Saturn, Neptune has internal heat source. Neptune radiates more than twice as much energy as it receives from Sun.
orbit
Neptune is 30 times farther from Sun than Earth, 4,500,000,000,000 meters from Sun. Circular orbit of 165 years slightly inclines to ecliptic.
layers
Neptune has rocky core, 16,000,000-meter diameter. Around core is ice 8,000,000 meters thick. Around that layer is molecular hydrogen.
atmosphere
Atmosphere is mostly hydrogen and helium with some methane. Blue color results from red-light absorption by methane. Neptune has argon clouds. Neptune has rapid winds in horizontal bands and has large storms or vortices. Winds are fastest in solar system, reaching 2000 kilometers per hour. Large dark oval revolves around Neptune every 18 hours. Second dark spot revolves around Neptune every 16 hours.
moons
Neptune has many moons. Triton is main moon and is bigger than Moon. Gravitational effect of smaller moon defines rings. Adams Ring is 63,000 km from center of Neptune. Leverrier Ring is 53,000 km. Galle Ring is 42,000 km. All rings are closer to Neptune than Moon is to Earth.
Solar system has dwarf planets {planetoid}.
Pieces {asteroid}| from former planetary formation lie between Mars and Jupiter, 2.6 x 10^6 miles from Sun. Asteroids cluster and so came from collisions between many bodies 50,000 to 200,000 meters diameter. More than 10,000 asteroids exist. 2000 are relatively large.
names
Ceres has diameter 800,000 meters and is largest. Pallas, Juno, Vesta, and Hygiea have diameter more than 200 miles. Trojans are at the two stable Lagrangian points in Jupiter's orbit. Apollos go inside orbit of Mercury. Icarus goes to within 1.9 x 10^6 miles of Sun.
orbit
Asteroids have elliptical orbits. Jupiter gravity and asteroid collisions cause some orbits to be so elliptical that they go within 30,000,000,000 meters of Sun.
meteors
Meteors are asteroids. Iron meteorites {S class meteorite} are 10^9 years old. Stony meteorites are 1 x 10^6 to 100 x 10^6 years old. They are the main asteroids in inner asteroid belt. Carbonaceous chondrite meteorites {C class meteorite} {D class meteorite} are 4.6 x 10^9 years old and have solid grains from original solar-cloud dust. They are the main asteroids in outer belt and are darker and redder. Type C1 has same composition as Sun, with no silicate pea-size chondrules. Types C2 and C3 have iron, nickel, and rock, unlike Sun, and have chondrules.
Planetoids {centaur, solar system}, such as Chiron, can orbit elliptically between Neptune and asteroid belt. Composition is like meteorites and comets.
Solar system has an icy-planetoid ring {Kuiper belt}|, starting at Neptune and extending to Pluto, 4.6 billion miles from Sun. Kuiper-belt planetoids can orbit once every 200 to 400 years. Planetoids, such as Eris (Xena or 2003 UB313), can have highly elliptical orbits. Eris [2005] has methane surface, is three times larger than Pluto, has small moon (Gabrielle), and orbits at 45 degrees to ecliptic. Astronomers also discovered Sedna [2003] and Quaoar [2002].
plutino
Pluto and other planetoids {plutino} can orbit in resonance with Neptune. As Neptune orbits thrice, they orbit twice.
Small planets {Pluto, planetoid} are planetoids.
properties
Diameter is 2,400,000 meters. Mass is 0.1 Earth mass. Density is probably like that of rock. Gravity is less than Moon gravity.
properties: rotation
Pluto rotates every 6.4 days.
properties: temperature
Surface temperature is 43 K.
properties: orbit
Pluto averages 5,900,000,000,000 meters from Sun, with highly elliptical orbit of 248 years, inclined 17 degrees to ecliptic. It has seasons. Pluto is in Kuiper belt.
surface
Surface has frozen nitrogen, carbon monoxide, methane, and water.
atmosphere
Atmosphere is rapidly evaporating.
moons
Pluto has one moon, Charon, 1,200,000-meter diameter and 19,000,000 meters away.
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Date Modified: 2022.0225