The Planets Ali Nork

Planetary Revolution Planets revolve counterclockwise around Sun Planets revolve counterclockwise around Sun Planets revolve on a common plane called the ecliptic Planets revolve on a common plane called the ecliptic Pluto’s orbit is tipped 17.2°Pluto’s orbit is tipped 17.2° Other planets tipped no more than 3.4°Other planets tipped no more than 3.4°

Planetary Rotation Almost all planet rotate counterclockwise, but Almost all planet rotate counterclockwise, but Venus rotates backwards (retrograde)Venus rotates backwards (retrograde) Uranus and Pluto rotate on sides w/ equator perpendicular to orbitUranus and Pluto rotate on sides w/ equator perpendicular to orbit

Inner Planets Terrestrial, or “earthlike” Terrestrial, or “earthlike” Mercury, Venus, Earth, Mars Mercury, Venus, Earth, Mars Closer to sun Closer to sun Small diameter/mass Small diameter/mass Density greater than water (3- 5g/cm 3 ) Density greater than water (3- 5g/cm 3 ) Rocky crust, dense mantle Rocky crust, dense mantle Very dense core w/ Fe and Ni Very dense core w/ Fe and Ni

Inner planets cont’d…. Impact craters Impact craters Few moons (actually- Mercury and Venus have no moons) Few moons (actually- Mercury and Venus have no moons) Less atmosphere Less atmosphere Animation here Animation herehere

Outer Planets Jovian planets- Jupiter-like Jovian planets- Jupiter-like Gas giants- Jupiter, Saturn, Uranus, Neptune Gas giants- Jupiter, Saturn, Uranus, Neptune Huge compared to Earth Huge compared to Earth Large mass, low density (<1.75g/cm 3 ) Large mass, low density (<1.75g/cm 3 ) Mostly gaseous (H and He) Mostly gaseous (H and He)

Outer Planets cont’d…. Have rings Have rings Have many moons- Jupiter (63), Saturn (62), Uranus (27), Neptune (13) Have many moons- Jupiter (63), Saturn (62), Uranus (27), Neptune (13) Separated from terrestrial planets by the Asteroid Belt Separated from terrestrial planets by the Asteroid Belt

What’s Up With Pluto? Was considered a planet for 76 years Was considered a planet for 76 years reclassified as a dwarf planet reclassified as a dwarf planet Mostly ice Mostly ice Very small (1/20 the mass of Mercury) Very small (1/20 the mass of Mercury) Has 3 moons (Charon, Nix and Hydra) Has 3 moons (Charon, Nix and Hydra) Highly eccentric (elliptical) orbit which crosses Neptune’s Highly eccentric (elliptical) orbit which crosses Neptune’s

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Origin of the Solar System Solar nebula model- ss formed out of an eastward rotation interstellar cloud 5 billion years ago Solar nebula model- ss formed out of an eastward rotation interstellar cloud 5 billion years ago Dust and gas cloud (mostly H and He)Dust and gas cloud (mostly H and He) Cloud condensed due to gravity; speed of rotation increased; became flattened Cloud condensed due to gravity; speed of rotation increased; became flattened Densest area in middle became the sun Densest area in middle became the sun

Disk eventually cooled; different elements and compounds condensed depending on distance from sun Disk eventually cooled; different elements and compounds condensed depending on distance from sun Tiny grains of condensing material accumulated and collided; eventually formed planetismals (“baby planets”) Tiny grains of condensing material accumulated and collided; eventually formed planetismals (“baby planets”) Jupiter was the first large planet to form in outer ss; probably prevented other outer planets from growing larger Jupiter was the first large planet to form in outer ss; probably prevented other outer planets from growing larger Asteroid belt (interplanetary debris between Mars and Jupiter) remains b/c Jupiter’s gravity prevented it from creating a planet Asteroid belt (interplanetary debris between Mars and Jupiter) remains b/c Jupiter’s gravity prevented it from creating a planet

Planetary Formation Terrestrial planets formed where temps were very high and metals and silicates could form solids Terrestrial planets formed where temps were very high and metals and silicates could form solids Jovian planets formed at lower temps where gas became ice Jovian planets formed at lower temps where gas became ice No planets in asteroid belt b/c Jupiter is so massive and its gravity disturbed planet formation No planets in asteroid belt b/c Jupiter is so massive and its gravity disturbed planet formation Larger mass enables planets to hang onto particles in rings; less impacted by solar wind (far away from sun) Larger mass enables planets to hang onto particles in rings; less impacted by solar wind (far away from sun)

Planetary Satellites Moons are natural planetary satellites that revolve around a planet Moons are natural planetary satellites that revolve around a planet Some cool moon facts: Some cool moon facts: Jupiter’s moon Ganymede is the largest one in our solar systemJupiter’s moon Ganymede is the largest one in our solar system Saturn’s moon Titan has a mostly nitrogen atmosphere and has liquid hydrocarbon lakes; also has water iceSaturn’s moon Titan has a mostly nitrogen atmosphere and has liquid hydrocarbon lakes; also has water ice Mars has 2 tiny moons (Phobos and Deimos) which may be captured asteroidsMars has 2 tiny moons (Phobos and Deimos) which may be captured asteroids

Ganymede

Titan

Phobos and Deimos

Voyager I “family portrait” family portraitfamily portrait -Taken in 1990 after Voyager I and II left Pluto’s probit

Asteroids Rocky masses that revolve around Sun; usually between Mars and Jupiter Rocky masses that revolve around Sun; usually between Mars and Jupiter Debris left over by a planet that failed to from (about 2.8 AU from Sun) Debris left over by a planet that failed to from (about 2.8 AU from Sun) Need a telescope to view them Need a telescope to view them Largest is Ceres (578 mi wide) Largest is Ceres (578 mi wide)

Comets Nucleus of ice and debris; coma is gas surrounded by nucleus Nucleus of ice and debris; coma is gas surrounded by nucleus

Comets cont’d… Tail points away from sun and is caused by solar wind Tail points away from sun and is caused by solar wind Long, eccentric orbit which goes outside the 9 (or 8) planets Long, eccentric orbit which goes outside the 9 (or 8) planets Orbital periods can be long or short Orbital periods can be long or short Comet Shoemaker-Levy 9 slammed into Jupiter’s atmosphere in 1994 Comet Shoemaker-Levy 9 slammed into Jupiter’s atmosphere in 1994

Kuiper Belt Located beyond planet Neptune Located beyond planet Neptune Home to over 700,000 icy, small objects (Pluto, Quaoar) Home to over 700,000 icy, small objects (Pluto, Quaoar) Sometimes objects are redirected towards the sun (disturbed by gravity of one of the gas giants) Sometimes objects are redirected towards the sun (disturbed by gravity of one of the gas giants)

Oort Cloud Home to many comets Home to many comets Located 50,000 AU from the sun Located 50,000 AU from the sun Outer edge defines the boundary of our solar system Outer edge defines the boundary of our solar system Members include Sedna and various comets Members include Sedna and various comets

Meteoroids Rocky, icy fragment in space Rocky, icy fragment in space Range in size from small sand particles to boulders Range in size from small sand particles to boulders Meteor (shooting star) is light produced when enters Earth’s atmosphere due to friction Meteor (shooting star) is light produced when enters Earth’s atmosphere due to friction Meteorite is meteoroid that has struck Earth’s surface Meteorite is meteoroid that has struck Earth’s surface May produce impact cratersMay produce impact craters

Meteoroids cont’d… Meteoroids can’t be seen, but meteors can b/c of light produced Meteoroids can’t be seen, but meteors can b/c of light produced Maybe formed from impacts between asteroids Maybe formed from impacts between asteroids Micrometeoroids- tiny fragments that often hit Earth Micrometeoroids- tiny fragments that often hit Earth Can travel at high speeds and damage spacecraftCan travel at high speeds and damage spacecraft