part 3: a trip through the solar system 1. measuring distances astronomical units or au: one...
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THE SOLAR SYSTEM
Part 3: A Trip through the Solar System
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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
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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):
MercuryVenusEarthMarsJupiterSaturnUranusNeptune
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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:
CeresPlutoHaumeaMakemake Eris.
There are nearly 50 other known objects that may be dwarf planets and as many as 2,000 in all.
Only two well observed.
Ceres
Eris Pluto
Pictures from Hubble Telescope
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Major Features – Planets and Dwarf Planets
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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
Image Credit: NASA/JPL/JHUAPL
This picture of Eros is the first of an asteroid taken from an orbiting spacecraft.
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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 2004. Credit: National Science Foundation
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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.
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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
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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
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Major Features: Kuiper Belt Discovered in 1992, but hypothesized as early as
1930, soon after the discovery of Pluto 30-100 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.
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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 DysnomiaEris, 27% more massive than
Pluto, was discovered in 2003. Hubble Photograph
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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?
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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
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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
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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
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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
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Jupiter’s Moons Jupiter has dozens of moons Four were discovered by Galileo
Galilei and are called the Galilean satellites or moonsIo – innermost; most geologically
active object in solar systemEuropa - 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
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, CallistoCredit: NASA/JPL/DLR
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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
Saturn in natural color, photographed by Cassini
Credit: NASA/JPL/Space Science Institute
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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
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
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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 1989. The picture shows the Great Dark Spot and its companion bright smudge.Credit: NASA
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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 surfaceMost contain iron, nickel,
and stone
The Hoba meteorite in 2006. Located in Namibia, it is the largest known meteorite on Earth, about 54,000kg.
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