The Planets Ali Nork

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

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

Inner Planets Terrestrial, or “earthlike” Mercury, Venus, Earth, Mars Closer to sun Small diameter/mass Density greater than water (3-5g/cm3) Rocky crust, dense mantle Very dense core w/ Fe and Ni

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

Outer Planets Jovian planets- Jupiter-like Gas giants- Jupiter, Saturn, Uranus, Neptune Huge compared to Earth Large mass, low density (<1.75g/cm3) Mostly gaseous (H and He)

Outer Planets cont’d…. Have rings Have many moons- Jupiter (67), Saturn (62), Uranus (27), Neptune (14) Separated from terrestrial planets by the Asteroid Belt

What’s Up With Pluto? Was considered a planet for 76 years 2006- reclassified as a dwarf planet Mostly ice Very small (1/20 the mass of Mercury) Has 3 moons (Charon, Nix and Hydra) Highly eccentric (elliptical) orbit which crosses Neptune’s

http://en.wikipedia.org/wiki/Image:TheKuiperBelt_Orbits_Pluto_Ecliptic.svg

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

Planetary Formation 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 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)

Planetary Satellites Moons are natural planetary satellites that revolve around a planet Some cool moon facts: Jupiter’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 ice Mars has 2 tiny moons (Phobos and Deimos) which may be captured asteroids

Ganymede

Titan

Phobos and Deimos

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

Asteroids 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) Need a telescope to view them Largest is Ceres (578 mi wide)

Comets 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 Long, eccentric orbit which goes outside the 9 (or 8) planets Orbital periods can be long or short Comet Shoemaker-Levy 9 slammed into Jupiter’s atmosphere in 1994

Kuiper Belt Located beyond planet Neptune 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)

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

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

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