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