Formation and Evolution of the Solar System

1. Chapter 27 The Solar System

2. Chapter 27-1 What is the Solar System? Solar System- Sun and all the objects that orbit the Sun. Nebula- Cloud of dust and gas in space. • *The Solar System is believed to have formed according to the nebular hypothesis, first proposed in 1755 by Immanuel Kant and independently formulated by Pierre-Simon Laplace. This theory holds that 4.6 billion years ago the Solar System formed from the gravitational collapse of a giant molecular cloud. This initial cloud was likely several light-years across and probably birthed several stars.

3. Evolution of Our Solar System • The region that would become the Solar System, known as the pre-solar nebula, had a diameter of between 7000 and 20,000 AU and a mass just over that of the Sun (by between 0.1 and 0.001 solar masses). As the nebula collapsed, conservation of angular momentum made it rotate faster. As the material within the nebula condensed, the atoms within it began to collide with increasing frequency. The center, where most of the mass collected, became increasingly hotter than the surrounding disc. As gravity, gas pressure, magnetic fields, and rotation acted on the contracting nebula, it began to flatten into a spinning protoplanetary disk with a diameter of roughly 200 AU and a hot, dense protostar at the center.

4. The Hot Protostar Becomes Our Sun Sun- Dense mass of spinning gas that formed at the center of Our Solar System. *The Sun contains more than 99.8% of the mass that makes up our Solar System. The Sun’s family is made up of nine planets, eight with a 2006 reclassification of Pluto. More than 90 moons, countless chunks of rock debris, ice and gas. All together the Solar System fills a volume of space 10 trillion in diameter. Planet- Comes from a Greek word meaning, “wanderer”. All the planets orbit the Sun in the same direction. Orbit- curved path of one object around another object in space.

5. Planet Formation • After 100 million years, the pressure and density of hydrogen in the centre of the collapsing nebula became great enough for the protosun to begin thermonuclear fusion. This increased until hydrostatic equilibrium was achieved, with the thermal energy countering the force of gravitational contraction. At this point the Sun became a fully fledged star. • From the remaining cloud of gas and dust (the "solar nebula"), the various planets formed. They are believed to have formed by accretion: the planets began as dust grains in orbit around the central protostar; then gathered by direct contact into clumps between one and ten kilometers in diameter; then collided to form larger bodies (planetesimals) of roughly 5 km in size; then gradually increased by further collisions at roughly 15 cm per year over the course of the next few million years. • Once the young Sun began producing energy, the solar wind (see below) blew the gas and dust in the protoplanetary disk into interstellar space and ended the growth of the planets.

6. The Sun and the Planets • The inner solar system was too warm for volatile molecules like water and methane to condense, and so the planetesimals which formed there were relatively small (comprising only 0.6% the mass of the disc) and composed largely of compounds with high melting points, such as silicates and metals. These rocky bodies eventually became the terrestrial planets.

7. The Outer Planets • Farther out, the gravitational effects of Jupiter made it impossible for the protoplanetary objects present to come together, leaving behind the asteroid belt. • Farther out still, beyond the frost line, where more volatile icy compounds could remain solid, Jupiter and Saturn became the gas giants. Uranus and Neptune captured much less material and are known as ice giants because their cores are believed to be made mostly of ices (hydrogen compounds).

8. Chapter 27-2 What do we know about orbits? Ellipse- flattened circle, or oval. * What causes our Planets to stay close to the sun? Gravity- force acting on any object that has a mass. * The Sun is not in the center of the Earth’s orbit. The Earth is not equidistance from the Sun. Perihelion- point in a planet’s orbit at which it is closest to the Sun. Aphelion- point in a planet’s orbit at which it is furthest from the Sun. Orbital Velocity- The speed at which a planet travels in its orbit. * The closer a planet is to the Sun the faster its orbital velocity. * A planet moves fastest at perihelion and slowest at aphelion. * A planets orbital velocity is influenced by the force of gravity acting on it.

9. Chapter 27-3 The Earth’s Moon Moon- Solid rock like body that orbits the Earth. * On July 20, 1969- American Astronaut Neil Armstrong was the first but not the last human on the Moon’s surface. *The Moon’s distance from the Earth is 384,000 km. * The Moon is much smaller than the Earth(12,390 km). Equatorial diameter 3,400 Km. Which means less gravity, about 1/6th. * Has no liquid water or atmosphere. Has extremes of temperature, over 100°C to below -200°C.

10. The Moon’s Surface Mare (Maria)- broad, flat plain on the Moon’s surface. Crater- round holes on the Moon’s surface. *Galileo first saw the Moon with his telescope. He called the smooth dark areas Maria- which means “sea”. The light areas that he saw on the Moon were mountains or highlands. Another feature which he saw on the Moon was its many craters. These craters were believed to have formed from meteorites and volcanic activity.

11. Chapter 17-4 Satellite- Natural or artificial object orbiting another body in space. *Six of the Solar Systems planets have moons; Earth, Mars, Jupiter, Saturn, Uranus and Neptune. *Jupiter has 28 known moons. Ganymede is the largest @5,268 Km. *Saturn has 30 known moons. Titan is the second largest moon in the solar system. *Uranus has 21 known moons. *Neptune has 8 known moons. Triton is the largest and has the coldest surface in the solar system @ -235°C. Moons of Jupiter

12. Chapter 17-5 Inner Planets Characteristics of the Inner Planets Mercury- Planet closest to the Sun. Fastest orbit No Atmosphere/covered with craters Temperature Extremes- Daylight 430°C, Night -170°C. Explored by Mariner 10 (1974)

13. Chapter 17-5 Inner Planets Venus Similar to Earth in size, mass, and density. Highest average temperature/Air pressure 90 times greater than the a Earth. Atmosphere- Carbon Dioxide and Sulfuric Acid. Has a retrograde rotation- spins slowly in the opposite direction from other Planets.

14. Chapter 17-5 Inner Planets Earth Fifth largest planet in the Solar System. Only planet known to have liquid water oceans. Only planet known to support life.( Temperature/Atmospheric gases) Has a magnetic field caused by iron in its outer core.

15. Chapter 27-6 Inner Planets Mars Rift- valley caused by a crack in the crust of a planet. Orbital period- 687 Earth days, Rotational period 4 hrs. 37 min. The red planet. Has seasonal periods. Why? Has many volcanoes, valleys, polar ice caps, and extinct river channels. Largest known volcano in the solar system- Olympus (27Km) Atmosphere- thin layer of Carbon dioxide. Air pressure same as the Earth@35Km. Frequent dust storms, frozen water. Explored by- Viking Landers

16. Chapter 27-7 Asteroids and Meteoroids Asteroids- large chunk of rock or metal that orbits the Earth. Meteoroid- small piece of rock or metal that travels through space. Meteor- rock or metal that enters Earth’s atmosphere. Meteorite- piece of rock or metal that falls on a planet or moon’s surface. * Asteroids are left over debris from the formation of the solar system. * Asteroids are located in the asteroid belt, between Mars and Jupiter. * Meteoroids are formed when asteroids collide and break into smaller pieces. * Meteoroids that enter the Earth’s atmosphere are called meteors. They streak across the night time sky leaving a long streak of light. If they don’t burn up, they strike the Earth creating a crater.

17. Chapter 27-7 Asteroids and Meteorites Meteor Showers- Multiple meteor flashes seen at night. *Cause- when comets pass close to the Sun they melt, releasing tiny sand grain sized particles that enter the Earth’s atmosphere and burn up. * Most meteorites that strike the Earth’s fall into the ocean’s. Why? * Many meteorites can be found in the Antarctic region. Easy to find. * Meteorites that strike the Earth are relatively small. Once in a rare occasion a asteroid which is large will strike the Earth. Not good! Just ask a dinosaurs. * An rare element called iridium is associated with asteroids and comets.

18. Chapter 27-8 Gas Giants Jupiter Largest planet in the solar system. Gas giant with a rocky core. Composition is mostly light gases-hydrogen and helium. Colorful bands of gases cover the planet. All the gas planets have rings. Rings are made of small dust and ice particles. The Great red spot on Jupiter is believed to be a large cyclonic storm. Believed to be made of steam and ammonia rising from its atmosphere.

19. Chapter 27-8 The Ringed Planet Saturn The second largest planet in the solar system. Gas giant made mostly of hydrogen and helium. Saturn is less dense than water. Yes, it would float in our oceans. Saturn’s rings are its most distinctive feature. There are three main rings and thousands of smaller rings. Cassini division- the name given to the large gap between two rings.

20. Chapter 27-9 Uranus and Neptune Uranus Third largest planet in the solar system. First planet to be discovered using a telescope (1781) Explored by Voyager 2 (1986) fly by. Made mostly of hydrogen and helium. The blue-green color indicates that the atmosphere contains methane. Its polar Axis are horizontal. The poles point towards the Sun. May be caused by an earlier collision with another planet sized body. Rotational velocity is very fast and has a strong magnetic field. It also contains a faint ring.

21. Chapter 27-9 Neptune Gas Giant Neptune Neptune is similar to Uranus in size and mass. Contains a faint ring around the equator. Discovered in 1845. Visited by Voyager 2, which discovered a Great Dark Spot. Atmosphere- upper atmosphere is made mostly of frozen clouds of methane, which gives it the blue-green color. Lower atmosphere contains mostly hydrogen and helium. Windiest planet- winds blow from east to west and can reach speeds of 1,500km/h

22. Chapter 27-10 Comets Comet- lump of ice, frozen gas, and dust that orbits the Sun. Nucleus- head or solid part of a comet. Coma- gas cloud that surrounds the nucleus of a comet. Tail- long, ribbon like trail of comet dust and gas. * A comet orbits the Sun in a long ellipse. * Core is a dirty ice ball consisting of rock debris, dust frozen water and gas. * The tail is formed by a stream of particles coming from the Sun. As the comet gets closer to the Sun it melts and releases much of the gas, dust and particles frozen in its nucleus. Tails can stretch for millions of miles.

23. Chapter 27-10 Comets Where do comets form? * Comets are believed to come from the Oort cloud located far beyond Pluto. * Some astronomers believe that comets can come from the Kuiper belt located beyond Neptune. * Comets formed billions of years ago when the solar system was forming. Larger pieces of rock, dust and gas formed the planets and moons. Smaller pieces of dust, gas, ice, rock and metal formed comets and asteroids.

24. Chapter 27-10 Comet Research * Stardust mission craft