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The Solar System Essential Questions What is the difference between a planet and a dwarf planet? What is the difference between a meteor and a meteorite? What is the difference between an asteroid and a comet? How do we determine how far apart the planets are? How do the solar system bodies orbit the sun? What is the difference between a planet and a dwarf planet? IAU definition of Planet Former definition • A non-luminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. A planet is a celestial body that • (a) is in orbit around the Sun, • (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and • (c) has cleared the neighbourhood around its orbit. IAU definition of a Dwarf Planet A "dwarf planet" is a celestial body that • (a) is in orbit around the Sun, • (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, • (c) has not cleared the neighbourhood around its orbit, and • (d) is not a satellite. Types of Planets Terrestrial Planets Jovian Planets Dwarf Planets Terrestrial Planets Smaller size and mass Higher density Made mostly of rock and metal Solid surface Few, if any, moons No rings Closer to the Sun and each other Warmer surfaces Mercury, Venus, Earth, Mars Video “A Spin Around the Solar System: Our Rocky Neighbors: The Inner Planets” Mercury Diameter = 4872 km Distance to the Sun =57.9 million km Mars Diameter =6 780 km Distance to the Sun =227.9 million km Venus Diameter =12 104km Distance to the Sun = 108.2 million km Earth Diameter =12 756 km Distance to the Sun =149.6 million km Orbit period = 356.26 days Orbit speed = 108 000 km/s Axis rotation = 23.93 hours Axis tilt = 23.5o Acceleration = 9.81 m/s2 Jovian Planets Larger size and mass Lower density Mostly made of hydrogen, helium, and hydrogen compounds No solid surface Many moons Rings Farther from the sun and each other Cool temperatures at cloud tops Jupiter, Saturn, Uranus, Neptune Video “A Spin Around the Solar System: The Outer Planets the Gas Giants” Jupiter Diameter =142 984 km Distance to the Sun =778.4 million km Saturn Diameter =120 536 km Distance to the Sun =1.4 billion km Uranus Diameter =51 118 km Distance to the Sun =2.4 billion km Neptune Diameter =49 532 km Distance to the Sun = 4.5 billion km Dwarf Planets Pluto, Ceres, Eris Video “A Spin Around the Solar System: The Small Pieces: Asteroids, Comets, and Pluto” Ceres Diameter = 974.6km Distance to the Sun = 413 832 587.5 km Pluto Diameter =2 306km Distance to the Sun = 5 906 376 272km Eris Diameter =2 600km Distance to the Sun = 67.665AU What is the Difference Between a Meteor and a Meteorite? meteoroid is a sand- to bouldersized particle of debris in the Solar System meteor is the visible path of a meteoroid that enters Earth's (or another body's) atmosphere What is the difference between an asteroid and a comet? What is an Asteroid? IAU Definition (a) orbits the Sun inside the orbit of Jupiter (b) does not have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape (it is not round shaped), (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite. Asteroids Small bodies Believed to be left over from the beginning of the solar system billions of years ago 100,000 asteroids lie in belt between Mars and Jupiter Largest asteroids have been given names made of rocky and metallic minerals random shapes appear more clear than comets when viewed through a telescope Where are the asteroids? Most asteroids are located in two regions: •Asteroid belt •Orbit of Jupiter… the Hildas (the orange "triangle" just inside the orbit of Jupiter) and the Jovian Trojans (green). The group that leads Jupiter are called the "Greeks" and the trailing group are called the "Trojans" Asteroid Belt Discovered in 1801 Previously predicted by Franz Xaver Von Zach 1801- Piazza found Ceres Olbers found Pallas and Vesta Asteroid Belt The region of space between Mars and Jupiter; about 2.8AU Hundreds of thousands of asteroids known. Probably millions more! 3 types of asteroid: Carbonaceous, Silicate, Metallic Even the largest object in the belt, Ceres (dwarf planet), is too dim to see without aid Remnants of a planet-formation process that failed due to Jupiter’s gravitational pull OR a planet that was broken apart during a collision What are Comets? Comets Small icy bodies Travel past the Sun Give off gas and dust as they pass by made of chemical compounds that vaporize when heated more elliptical (egg) shaped appear fuzzier than asteroids when viewed through a telescope grow tails as they get closer to the Sun highly elliptical orbits Anatomy of a Comet Anatomy of a Comet Parts of a Comet Nucleus= main mass of ice/frozen gas Coma = cloud of gas surrounding nucleus Tail = forms when ice vaporizes as comet approaches Sun Hydrogen cloud = cloud of gas that surrounds coma (only some comets have these) http://science.nationalgeographic.com/science/space/solar-system/asteroids-comets-article.html Where are the comets? Kuiper Belt A large body of small objects orbiting (the short period comets <200 years) the Sun in a radial zone extending outward from the orbit of Neptune (30 AU) to about 100 AU. Pluto maybe the biggest of the Kuiper Belt object. Oort Cloud Long Period Comets (period > 200 years) seems to come mostly from a spherical region at about 50,000 AU from the Sun. Kuiper Belt Discovered in 1992 Named for Dutch Astronomer Gerard Kuiper, who had PREDICTED its existence in 1951. Kuiper Belt Region beyond Neptune; 30 to over 50AU At least 70,000 small, icy, slowmoving, objects Very faint objects because small, far and reflect light from Sun A million times fainter than faintest we can see with naked-eye Oort Cloud Hypothetical spherical cloud. No direct observations. Proposed by Ernst Opik (1932), Jan Henrik Oort (1950) Oort Cloud 50,000AU; defines gravitational boundary of solar system Source of long-period comets (comets that have an orbit of hundreds or thousands of years) Objects composed of ices (water, methane, and ammonia) 2 regions: • outer sphere • inner disc What are the Types of Comets? Short-period comets • periods of less than 200 years, • are returning as predicted on wellknown orbits Long-period comets • periods of more than 200 years • among the brightest have been several How do we determine how far apart the planets are? Bode’s Law •A rough rule that predicts the spacing of the planets in the Solar System •To find the mean distances of the planets, beginning with the following simple sequence of numbers: 0 3 6 12 24 48 96 192 384 •With the exception of the first two, the others are simple twice the value of the preceding number. •Add 4 to each number: 4 7 10 16 28 52 100 196 388 •Then divide by 10: 0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 38.8 Planet Actual Distance (AU) Bode’s Law Mercury 0.39 0.4 Venus 0.72 0.7 Earth 1.00 1.0 Mars 1.52 1.6 Jupiter 5.20 5.2 Saturn 9.54 10.0 Uranus 19.2 19.6 Neptune 30.1 38.8 Works for moons too! How do the solar system bodies orbit the sun?