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11.2 The Sun and the Planets See pages 382 - 383 Our Sun, an average star in the universe, is the center of our solar system. 1) Our solar system is full of planets, moons, asteroids and comets, all of which revolve around the Sun at the center. 2) When a star forms from a nebula, gravity pulls most of the material into the new star, but some may also clump together to form objects in a solar system. This is the Nebular Theory. a) A planet is a celestial body that orbits one or more stars. b) Each planet may also spin on its axis (rotates) while it orbits the Sun (revolves). 3) Our solar system formed approximately 4.5 billion years ago. 4) The four inner (rocky) planets formed in the first 100 million years on the Sun’s existence, while the outer (gas) planets formed later from the remnants of the Sun’s original nebula. See pages 383 - 384 THE SUN 1) 2) 3) contains 99% of all the mass found in our solar system. has a diameter equal to 110 Earths. made up mostly of hydrogen. The hydrogen molecules -are forced to join together through massive gravity -form new helium molecules, then -release huge quantities of energy as light and heat through the process of thermonuclear fusion. 4) 5) 6) 7) has no solid surface has distinctive features such as sun spots, flares, and prominences. The photosphere is the surface of the Sun. It looks blotchy due to rising and cooling gases. The corona is the outer portion of the Sun’s atmosphere. SOLAR WINDS See page 385 Sometimes, gases from the Sun’s corona erupt outwards like a bursting soap bubble. 1) The resulting solar wind is full of high-energy particles that would kill any life on Earth they struck. 2) Luckily, our magnetic field deflects this solar wind. We can see these particles being deflected when we see the Northern Lights. 3) Large outbursts of solar winds can wreak havoc with satellites as well as Earth-bound energy supplies such as power plants. THE PLANETS See pages 385 - 387 1)To be considered a planet, a body must a) orbit one or more stars, b) be large enough that its own gravity holds it in a spherical shape, and c) be the only body occupying the orbital path. 2) Distances between planets in the solar system are measured in astronomical units (AU). -One AU = the average distance from the Sun to the Earth. a) The inner planets are relatively close to the center of the solar system I. Mars is 1.52 AU from the Sun. II. The next planet, Jupiter, an outer planet, is 5.27 AU from the Sun. III. The most distant planet, Neptune, is 30.06 AU from the Sun. Inner, rocky planets Outer, gaseous planets Mercury Smallest planet Jupiter Largest planet Venus Earth’s sister Saturn Rings + many moons Earth Only life in universe Uranus Methane gas planet Mars The red planet Neptune Outermost planet OTHER SOLAR SYSTEM BODIES See pages 388 - 389 There are also numerous celestial bodies smaller than planets in our solar system. Moons are found around all planets except Mercury and Venus. Asteroids are found mostly between Mars and Jupiter in the asteroid belt. It is thought these are ‘leftovers’ from the formation of the solar system. This picture of the rocky asteroid 951 Gaspra was taken by NASA's Galileo spacecraft. Image Credit: NASA The Kuiper Belt is a disk-shaped region past the orbit of Neptune, roughly 4,400,000,000 to 14,900,000,000 km (30 to 100 AU) from the Sun, that consists mainly of small bodies which are the remnants from the Solar System's formation. It also contains at least one dwarf planet - Pluto. Pluto is indeed now considered to be a member of the Kuiper Belt - the largest object belonging to it, in fact! Like other members of the Belt, it is composed primarily of rock and ice and is relatively small.. The Kuiper Belt is also believed to be the source for short-period comets (ie, those that take less than 200 years or orbit). http://heasarc.gsfc.nasa.gov/d ocs/cosmic/solar_system_info. html Comets (sometimes called “dirty snowballs”) are actually rocky travelers, following huge orbits far outside the planets in the Oort Cloud. Trans-neptunian objects refer to objects outside Neptune’s orbit, including ex-planet Pluto (now referred to as a dwarf planet). These objects orbit the Sun in a large area known as the Kuiper Belt. The Oort Cloud In 1950, astronomer Jan Oort proposed that long-period comets reside in a vast spherical cloud residing 50,000 to 50,000+ AU from the Sun, at the outer reaches of the Solar System. This major reservoir of comets has come to be known as the Oort Cloud. http://heasarc.gsfc.nasa.gov/docs/cosmic/solar_system_info.html The Kuiper belt can be described as disc or doughnut-shaped, but the Oort cloud is more like a very thick "bubble" that surrounds the entire solar system, reaching about half-way from the Sun to the next nearest star. Statistics imply that it may contain as many as a trillion (1012) comets. Unfortunately, since the individual comets are so small and at such large distances, we have no direct evidence for the Oort Cloud. The Oort Cloud is, however the best theory to explain how longperiod comets exist. The Oort Cloud is at the farthest reaches of the Sun’s gravitational pull, almost 25% of the way to the next nearest star, Proxima Centauri. https://www.youtube.com/watch?v=ZDaFQsdNNgU http://herschel.jpl.nasa.gov/solarSystem.shtml Artist’s rendering of the Kuiper Belt and Oort Cloud.