Touring Our Solar System Good link: http://solarsystem.nasa.gov/planets/ Chapter 23 200

The Solar System Ch. 23.1 What are the 2 “planetary neighborhoods”? inner planets outer planets What separates these 2 “neighborhoods?” asteroid belt

The Solar System What are the inner planets? 4 closest to sun Mercury Venus Earth Mars What is another name for the inner planets? “terrestrial” planets b/c earth-like characteristics rocky crusts dense mantle layers very dense cores Distance Between Planets Visualization

The Solar System What are asteroids? Where are asteroids located? solid, rocklike masses that orbit the sun in same direction as planets Where are asteroids located? between Mars & Jupiter in asteroid belt that separates inner planets from outer planets

The Solar System What are the outer planets? remaining 4 planets Jupiter Saturn Uranus Neptune What is another name for the outer planets? “Jovian” planets or Gas Giants How do they compare to the terrestrial planets? considerably larger than Earth gaseous less dense have ring systems Composed mainly of light elements  Hydrogen (H) & Helium (He) 3 common properties of ring systems: Consist of many particles in independent orbits around planet Closer to the planet than the major moons Orbit over the planet’s equator

The Solar System What about Pluto??? oddity of the solar system Not dense enough to be considered “terrestrial”. Too small to be “Jovian”.

The Terrestrial (Inner) Planets sec. 23.2 Fun Facts Mercury surface many craters No atmosphere (due to weak gravity)… So… no weather to erode craters smooth plains formed by lava flowing from cracks in surface extremely hot day temps (400+°C) & extremely cold night temps (-200°C) due to lack of atmosphere MESSENGER Orbits Mercury (AMNH Sci Bulletin)

Terrestrial (Inner) Planets: Fun Facts Venus “Earth’s twin/sister planet” similar diameter, mass, gravity Unlike other planets rotates east to west (clockwise) atmosphere = mostly carbon dioxide (CO2) “runaway” greenhouse effect (~475°C) yellow clouds = sulfuric acid All other planets rotate counterclockwise/west to east (if looking from top down)

Terrestrial (Inner) Planets: Fun Facts Mars Axis tilted at almost same angle & in same direction as Earth’s similar 4 seasons but ~2x as long (since year is ~2x longer than Earth’s) largest volcano in the solar system = Olympus Mons Valles Marineris canyon system (as long as U. S. is wide) Curiosity: Searching for Carbon (AMNH Sci Bulletin)

The Outer Planets: Fun Facts Ch. 23.3 Jupiter More than 2x mass of all other planets combined Colored zones & belts “Great Red Spot” May be calm area that rotates slowly in turbulent atmosphere

The Outer Planets: Fun Facts Ch. 23.3 Saturn less dense than water (1g/cm3) would float most visible ring system believed to be chunks of ice colored zones & belts rising & sinking gases fewer than Jupiter How Did Saturn Get Its Rings? (AMNH Sci Bulletin) Saturn System Is Showing Its Age (AMNH Sci Bulletin)

The Outer Planets: Fun Facts Ch. 23.3 Uranus inclination (tilt) of axis almost 90° So… rotates on its side may have been tipped by collision early in history of solar system blue tint from methane

The Outer Planets: Fun Facts Ch. 23.3 Neptune occasionally outside Pluto’s orbit b/c Pluto’s orbit sometimes brings Pluto closer to the sun than Neptune Astronomers predicted existence mathematically in 1846

The Outer Planets: Fun Facts Ch. 23.3 Pluto No longer “true” planet Now one of 40+ “dwarf” planets Not dense enough to be “terrestrial” & too small to be “Jovian”. Smaller than 7 moons in our solar system (including our moon) New Horizons probe to Pluto launched Jan. 2006 will fly by Pluto & Charon ~2015 Occasionally the 8th “planet” b/c Pluto’s orbit sometimes brings it closer to the sun than Neptune Every 248 years… For ~20 years… Switched to 8th “planet” in 1979 & then switched back to 9th “planet” on 2/11/1999 Thought to be larger than it is until 1978 when astronomers discovered that it had a moon about ½ its size Moon  Charon (Diameter ~ 1200 km) Since Pluto & Charon are similar in mass, some scientists consider them to be a “double planet” rather than a planet-moon system New Horizons will take advantage of Jupiter's gravity (planned 2007 flyby) which will boost the probe's velocity by 9,000 mph & get it to Pluto by 2015 Article on Why Pluto is No Longer Considered a Planet

Planetary Satellites What is a satellite? an object that orbits a planet Example of natural satellites? moons Example of artificial satellite? TV satellite, GPS satellite, etc.

Planetary Satellites Earth  moon = only natural satellite Mars  2 tiny irregularly shaped moons Phobos Deimos Jupiter  at least 63 moons 4 largest Galilean satellites (in honor of discoverer Galileo) Io Europa Ganymede Callisto Europa Surface marked by crisscross pattern of bright & dark lines resemble cracks in ice floes in Earth’s polar oceans Galileo mission took photographs & magnetic field data Evidence that a liquid ocean 100 km deep may exist below the surface If so, it is possible that life forms may have developed there perhaps getting energy from subsurface volcanic vents like those on Earth’s ocean floor

Planetary Satellites Saturn  at least 61 moons Titan only moon known to have substantial atmosphere Uranus  at least 27 moons 5 major moons Titania Oberon Umbriel Ariel Miranda Neptune  at least 13 moons Triton Nile-Like River Found on Moon of Saturn (AMNH Sci Bulletin)

Minor Members of the Solar System Ch. 23.4 What are asteroids? solid, rocklike masses probably left over from formation of solar system How do asteroids orbit? around sun in same direction as planets most have nearly circular orbits within asteroid belt between Mars & Jupiter Protecting Earth from Asteroid Impacts (AMNH Sci Bulletin) some have collided with Earth… probably caused extinction of dinosaurs 65 mya

Minor Members of the Solar System What are comets? “dirty snowballs” dust particles trapped in mixture of frozen water, carbon dioxide, methane, & ammonia Where are comets usually found? Most are Trans-Neptunian Objects (TNOs) spend most of their time beyond Neptune’s orbit Including in Kuiper Belt & Oort Cloud Most comets come from the Oort Cloud and the Kuiper Belt. TNOs = Any object in the solar system that orbits beyond Neptune

Minor Members of the Solar System A few comets have highly elliptical orbits taking them closer to the sun can become visible at night when icy surface is heated Forms coma (cloud of gas & dust that expands into space) tail points away from sun due to solar wind Halley’s Comet 76 years Comet Ison When in normal orbit (in Kuiper belt & Oort cloud) consist only of solid main body (nucleus) Halley’s Comet (after astronomer Edmund Halley who noticed & predicted pattern of return) Returns to inner solar system every 76 years Records of comet in 1531, 1607, 1682 Predicted return of comet in 1758/9 Returned again in 1835, 1910, 1986 Next return 2062 Comet Ison… first pass near Sun 11/28/2013 http://news.discovery.com/space/astronomy/comet-ison-barely-survives-thanksgiving-solar-roast-131129.htm

Minor Members of the Solar System What are meteors, meteoroids, & meteorites? rocky or icy fragments; smaller than asteroids meteoroid traveling in space meteor passing through Earth’s atmosphere “shooting star” meteorites hit Earth’s surface Large #s streak across night sky over a few hours = meteor shower Earth passes through debris left by a comet & particles from tail plunge through atmosphere as meteors… B/c Earth’s orbit crosses path of comets around same time each year, many meteor showers occur @ predictable times… named for the constellation from which they appear to originate (ex. Perseids, happen in Aug., appear to come from constellation Perseus) range in size from microscopic to kilometers in diameter all originate inside our solar system. Most are fragments of small rocky and metallic bodies that broke apart long ago and orbit the Sun in the asteroid belt between Mars and Jupiter. Many orbit for millions of years before colliding with Earth. contain a record of the conditions under which the early solar system formed some 4.6 billion years ago. By studying meteorites, we can learn details about how our solar system evolved into our Sun and planets, and how meteorite impacts could affect our future.

Minor Members of the Solar System What are the 3 basic types of meteorites? stony iron stony-iron Give info about: how solar system evolved possible effects of impacts Cape York Meteorite (Ahnighito) Willamette Meteorite Iron meteorites form when large enough asteroids have had molten interiors catastrophically collide with other asteroids. These huge collisions blast out material from the molten iron core of the asteroid on orbits that reach Earth after millions of years. contain a record of the conditions under which the early solar system formed some 4.6 billion years ago. By studying meteorites, we can learn details about how our solar system evolved into our Sun and planets, and how meteorite impacts could affect our future. Willamette Meteorite iron meteorite weighs 15.5 tons found in Oregon: largest ever found in U. S. & 6th-largest in world smooth surface melted during its blazing entry into the atmosphere, while the pits formed on the Earth's surface. The Cape York Meteorite (Ahnighito) iron meteorite so heavy that supports from the largest of the three pieces go straight down to the bedrock beneath the Museum. comes from the center of a small asteroid that broke apart. 4.5-billion-years-old (nearly as old as the Sun) Discovered in 1894 in Greenland slammed into Earth some 10,000 years ago.

Minor Members of the Solar System What are impact craters? bowl-shaped depressions that remain after meteor or other object hits Earth, other planet, moon ejecta (debris) rays radiate out from crater Arizona’s Barringer Meteor Crater Rare features on Earth (only ~150 known) Atmosphere burns up most meteoroids before they can hit the surface Earth is geologically active so continuously “erasing” craters Arizona’s Barringer Meteor Crater One of youngest (formed ~49,000 years ago) Iron meteorite ~45 meters in diameter struck Earth, exploded, left behind crater ~1200 meters in diameter