Chapter 27 Formation of the Solar System The sun and all of the planets and other bodies that revolve around the sun.

It all started with a Big Bang (theory).

The Nebular Hypothesis * 1796 (Immanuel Kant) The sun and the planets condensed at about the same time out of a collapsing cloud of gas and dust called a solar nebula. – About 4.6 billion years ago, the amount of gravity near one of these clouds increased as a result of a nearby supernova (or some other force). – The rotating cloud of gas and dust from which the sun and planets formed is called the solar nebula. – Energy from collisions and pressure from gravity caused the center of the solar nebula to become hotter and denser (10,000,000 o C). – Hydrogen fusion began… a star formed (we call ours the sun). – The sun contains about 99% of all the matter contained in the solar nebula.

– Planets started out as small bodies called planetesimals. – Some planetesimals joined together through collisions and the force of gravity to form protoplanets. – Collisions added mass to the protoplanets to become planets and some moons. – the four inner planets are the terrestrial planets of Mercury, Venus, Earth, and Mars. – The four outer planets are the gas giants of Jupiter, Saturn, Uranus, and Neptune.

Formation of solid Earth When Earth first formed, it was very hot. (hot enough to melt iron) – energy was produced when the planetesimals collided during formation The outer layers compressed the inner layers Radioactive materials present emitted high energy particles. Heat caused denser materials to sink toward the center, a process called differentiation, which led to the layers of the earth (crust, mantle, and core). Earth’s surface cooled and solid rock at the surface formed.

Formation of Earth’s atmosphere – Hydrogen and helium gas (less dense) rose to the surface of the earth and were then released into the atmosphere. They eventually escaped into space. – As Earth’s surface continued to form, volcanic eruptions were frequent and water vapor (H2O), carbon dioxide (CO2), nitrogen (N2), methane, sulfur dioxide, and ammonia were released. – This outgassing formed the atmosphere. – These gases reacted with radiation from the sun to form other components such as ozone (O3). – As life evolved, other gases, namely oxygen (O2), were added to the atmosphere (2 billion years ago).

Formation of Earth’s Oceans. Some scientists think that, in addition to outgassing, some of Earth’s water may have come from space in the form of ice from comets. As Earth cooled, water vapor condensed to form rain that collected on the surface. First it was all freshwater then later minerals such as salt (halite) were washed and eroded in to it.

Aristotle’s Model Geocentric Model of the Solar System 1 st model of the solar system Planets, stars and sun revolved around the earth. Geocentric means “earth-centered” Heavens are unchanging (perfect) Theory lasted about 2000 years Problem : – It did not explain how planets sometimes appear to move backwards in the sky relative to the stars = retrograde motion.

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Ptolemy’s Model Greek philosopher – proposed changes Planets moved in small circles (epicycles) as they revolved around the Earth. It actually explained retrograde motion pretty well.

Copernicus’ Heliocentric model 1543, polish astronomer Nicolaus Copernicus Heliocentric model of the Universe – “sun-centered” Planets revolve around the sun in the same direction but at different speeds and distances from the sun. Explained retrograde motion the best Fast moving planets passed slow moving planets which made them appear to move backwards.

Galileo Galilei Observed that four moons traveled around the planet Jupiter. Showed him that objects can revolve around other objects other than Earth.

Galileo Galilei Observed that mountains exist on Earth’s moon. Showed him that objects don’t have to be perfectly spherical and can be more like Earth

Kepler’s Laws #1 (based on observations by Tycho Brahe) 1.Law of ellipses - each planet orbits the sun in a path called an ellipse (oblong or oval, not a circle). - eccentricity is the degree of elongation of an elliptical orbit. The more eccentric the orbit the more elongated it is. (an eccentricity near “0” is almost a perfect circle).

Kepler’s Laws #2 (based on observations by Tycho Brahe) 2.Law of equal areas – describes the speed at which objects travel at different points in their orbits. - Objects move faster in their orbit when they are closer the sun. - equal areas are covered in equal amounts of time as an object orbits the sun.

Kepler’s Laws #3 (based on observations by Tycho Brahe) 3.Law of periods - describes the relationship between the average distance of a planet from the sun and the orbital period of the planet. - Orbital period is the time required for a body to complete a single orbit (planets further away take longer to complete an orbit). - allows Scientists to determine how far away a planet is from the sun. T 2 = a 3 T = earth years and a = AU Example: Jupiter’s orbital period is 11.9 Earth years (T), the square is 142; 142 is 5.2 cubed Jupiter is 5.2 AU from the sun.

Newton’s laws of motion 1 st Law: a moving body will remain in motion and resist a change in motion until an outside force acts on it – inertia. Because a planet does not follow a straight path, an outside force must cause the orbit to curve. Gravity! The gravitational pull of a larger object (sun) is that force.