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Part 3: A Trip through the Solar System

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1 Part 3: A Trip through the Solar System

2 Measuring Distances Astronomical Units or AU:
One astronomical unit is equal to the mean (average) distance of the Earth from the Sun. 1 AU = 149,597,000 km (rounded number) Used to indicate distance to objects within our solar system

3 Major Features - Planets
The definition of planet, set in 2006 by the International Astronomical Union (IAU) states that, in the Solar System, a planet is a celestial body which: is in orbit around the Sun, has sufficient mass to assume a nearly round shape, and has "cleared the neighborhood" around its orbit. 8 Planets (In order from nearest the Sun): Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune In the end stages of planet formation, a planet will have "cleared the neighborhood" of its own orbital zone, meaning it has become gravitationally dominant, and there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence. 

4 Major Features – Dwarf Planets
A dwarf planet is a large body which meets the other criteria for a planet but has not cleared its neighborhood. The IAU currently recognizes five dwarf planets in the Solar System:  Ceres Pluto Haumea Makemake Eris. Ceres Only two well observed. Eris Pluto There are nearly 50 other known objects that may be dwarf planets and as many as 2,000 in all. Pictures from Hubble Telescope

5 Major Features – Planets and Dwarf Planets

6 Major Features: Asteroids
Rocky, airless worlds that orbit our sun, but are too small to be called planets Several hundred thousand discovered Most are located in the doughnut-shaped asteroid belt between Mars and Jupiter Also called "minor planets" Near-Earth Objects (NEOs): Asteroids that pass close to Earth May be composed of rocks, minerals, and/or metals This picture of Eros is the first of an asteroid taken from an orbiting spacecraft. Image Credit: NASA/JPL/JHUAPL

7 Major Features: Comets
Cosmic, dirty snowballs of frozen water and gases, rock, and dust When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the sun for millions of kilometers. This image of Comet C/2001 Q4 (NEAT) was taken at the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, Ariz. on 7 May Credit: National Science Foundation

8 Major Features: Comets
Parts of a Comet: nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus by the heat of the sun, may be hundreds of thousands of kilometers in diameter; high-speed solar particles (solar wind) blows the coma materials away from the sun, forming a long, and sometimes bright, tail.

9 Major Features: Comets
Parts of a Comet: dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind

10 Major Features: Comets
Comets orbit the sun. Short-period comets take up to 200 years to make one orbit; originate in the scattered disc beyond Neptune Long-period comets: may take millions of years to make one trip around the sun; originate in the Oort Cloud Credit: NASA

11 Major Features: Kuiper Belt
Discovered in 1992, but hypothesized as early as 1930, soon after the discovery of Pluto AU from the sun Similar to the asteroid belt in that it consists of small bodies that never reached planet size Unlike asteroids, Kuiper belt objects (over 1,000 known so far) are composed largely of frozen substances such as methane, ammonia and water Home of dwarf planets Pluto, Haumea, and Makemake Kuiper rhymes with piper and viper.

12 Major Features: Scattered Disc
A region of space beyond the Kuiper Belt The innermost portion overlaps with the Kuiper Belt, but its outer limits extend much farther away from the Sun Now thought to be the origin of short-period comets Sparsely populated with icy minor planets. Home of dwarf planet Eris Scattered Disc Objects, or SDOs, are among the most distant, and thus the most cold, objects in the solar system. Eris and its moon Dysnomia Eris, 27% more massive than Pluto, was discovered in 2003. Hubble Photograph

13 Major Features: The Oort Cloud
A vast, spherical, icy cloud 50,000AU or more from the sun (almost a light year); remnant of the original protoplanetary disc Believed to be the origin of long-period comets Only hypothesized, no direct evidence exists – why? No direct evidence exists because comets are relatively small and the distance is too great to see them.

14 The Planets: Mercury Closest to sun Rocky
Slightly larger than the moon Almost no atmosphere to stop impacts so covered with craters Very long day (59 Earth days) leads to very hot days (427°C) and very cold nights (-170°C) One of the first images to be returned from MESSENGER's second flyby of Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

15 Planets: Venus Second from the sun; closest to Earth
About the same size, mass, and density as Earth Highly volcanic Rotates east to west, or retrograde (reversed from Earth) A Venusian day (243 Earth days) is longer than a Venusian year (225 days) Thick, toxic atmosphere (mostly CO2) traps heat in a runaway "greenhouse effect," with temperatures hot enough to melt lead. (Hotter than Mercury) Image of Venus in real color. The surface is obscured by a thick blanket of clouds of sulfuric acid.  Credit: NASA/Ricardo Nunes

16 Planets: Mars 4th from the sun
A cold, desert world with a thin atmosphere ½ the diameter of Earth Often called the Red Planet due to the reddish color of the high levels of iron oxide (rust) on its surface Has seasons, polar ice caps, dormant volcanoes, canyons and weather 2 small moons, Phobos and Deimos Largest known volcano in the solar system, Olympus Mons Water-ice clouds, polar ice, polar regions, and geological features can be seen in this full-disk image of Mars. Credit: NASA/JPL

17 Planets: Jupiter 5th planet from the Sun
Most massive planet in our solar system A gas giant resembling a star in composition (mostly H and He) but did not get large enough to ignite nuclear fusion Covered in clouds Great Red Spot is a massive storm that has lasted for hundreds of years A true-color image of Jupiter taken by the Cassini spacecraft. The Galilean moon Europa casts a shadow on the planet's cloud tops. Credit: NASA/JPL/University of Arizona

18 Jupiter’s Moons Jupiter has dozens of moons
Four were discovered by Galileo Galilei and are called the Galilean satellites or moons Io – innermost; most geologically active object in solar system Europa - close to size of our moon; one of the smoothest objects in the solar system, covered in ice Ganymede – largest natural satellite in the solar system (larger than Mercury) Callisto – 3rd largest moon in solar system; heavily cratered Io - brilliant oranges, reds, and yellows due to high sulfur content of surface; 400 active volcanoes make it the most geologically active object in the solar system; 4th largest moon in solar system Europa- with a layer of water surrounding the mantle of the planet, thought to be 100 kilometers thick. The smooth surface includes a layer of ice, while the bottom of the ice is theorized to be liquid water. Montage of Jupiter's four Galilean moons, in a composite image comparing their sizes and the size of Jupiter. From top to bottom: Io, Europa, Ganymede, Callisto Credit: NASA/JPL/DLR

19 Planets: Saturn 6th planet from the sun
Rings of mostly ice particles (water); discovered by Galileo A gas giant composed of mainly H and He Spins so fast it is flattened at the poles Has a density less than that of water (0.7g/cm3) Has 62 known (53 named) satellites Titan, 2nd largest moon in the solar system, has a nitrogen-rich atmosphere Note: Jupiter, Uranus, and Neptune, the other gas giants, also have rings, but not as prominent as Saturn’s. Saturn in natural color, photographed by Cassini Credit: NASA/JPL/Space Science Institute

20 Planets: Uranus 7th planet from the sun Discovered in 1781
A gas giant or sometimes called an ice giant Like Venus, rotation is retrograde (east to west) Axis tilted almost 90° so appears to be rotating on its side. Methane in its atmosphere gives it a blue tint 13 known rings; 27 known moons, named after characters from works of Shakespeare and Alexander Pope Tilt of axis gives extreme differences in sunlight from season to season; seasons are about 20 years long as a revolution takes 84 years. Uranus' moon Ariel (white dot) and its shadow (black dot) were caught crossing the face of Uranus in this Hubble Space Telescope image. Credit: NASA/Space Telescope Science Institute

21 Planets: Neptune 8th planet from the sun Discovered in 1846
Orbit takes 165 years 4th largest by diameter after Uranus Also a gas or ice giant Blue due to methane plus some unknown substance in the atmosphere 6 known rings; 13 known moons (Triton, the largest, has a retrograde orbit) Voyager 2 captured this image of Neptune in The picture shows the Great Dark Spot and its companion bright smudge. Credit: NASA

22 Meteoroids, Meteors, and Meteorites
Meteroids: chunks of metal or stone that orbit the sun Meteor: a streak of light produced by a meteoroid burning due to friction as it plunges through the atmosphere; a shooting star Meteorite: a meteoroid that strikes the Earth’s surface Most contain iron, nickel, and stone Most meteoroids are thought to come from asteroids or comets, but some meteorites have been found that may be from the moon and others from Mars. The Hoba meteorite in Located in Namibia, it is the largest known meteorite on Earth, about 54,000kg.

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