FORMATION OF THE SOLAR SYSTEM Section 19.3

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Objectives…  By the end of this section you WILL be able to…  Explain how early astronomers understand and describe the solar system  Explain why the solar system is arranged the way it is  Identify what is in the solar system besides planets  Explain how the moon formed  Explain how astronomers know about exoplanets

 By understanding how things form, scientists can determine where other planets may be located, what they could be made of, etc.  Ancient people like the Greeks, Romans, and Druids, used stories to explain star movements  The first model of the solar system put Earth at the center. (kinda egocentric isnt it?)  Actually, its geocentric, in 140 CE Ptolemy expanded this model

 Even though Ptolemy’s model was wrong, it was still used for over a thousand years  It wasn’t until 1543 when Nicolaus Copernicus proposed a heliocentric model of the solar system  In 1605 Johannes Kepler improved the model and made the orbits slightly elliptical, rather than circular

 Isaac Newton was the first to explain that gravity keeps the planets in orbit around the sun and satellites in orbit around planets  Every object in the universe (having mass & proximity) exerts some kind of gravitational force on every other object  All of classical physics is built on this assumption

The Nebular Hypothesis  Scientists estimate the solar system to be roughly 4.6 billion years old  A nebula is a large cloud of dust and gas in space, the hypothesis explains why objects that form in a disk will lie in the same plane, and have almost circular orbits in the same direction.

 Planets form by a process called accretion  It is basically the “sticking together” of particles in the disk  This also explains the difference in composition of the inner planets compared to the outer planets  See page 674 for a good view of the nebular hypothesis

Rocks in Space  Comets are small bodies of ice and cosmic dust that follows an elliptical orbit and gives off gas and dust in the form of a tail as it passes in front of the sun  Asteroids are large rocky bodies found mostly between Mars and Jupiter  Meteoroids are small pieces of rock that enter Earth’s atmosphere  Meteoroids do not contact the Earth’s surface, if they do they are called meteorites

 Comets give glues to the origin of the solar system  Comets are composed of dust and ice made from methane, ammonia, carbon dioxide, and water  Some comets contain silicon, magnesium, and iron  Comets are sometimes called dirty snowballs  Comets have tails when they come close to the sun

 During the formation of our solar system, some leftovers didn’t combine  The Oort Cloud is where comets tend to reside  The Oort Cloud may be up to 100,000 AU wide  Halley’s Comet is one of the most famous it travels an eliptical orbit and appears in Earth’s sky every 76 years  It will appear again August 20 th 2061 and will pass within.05 AU of Venus  In 2134 Halley’s comet will pass closer than.1 AU of Earth

 Meteorites can be made up of many types of elements  There are three major types of meteorites 1. Stony 2. Iron 3 Stony iron  Meteoroids sometimes strike earth  Objects smaller than 10m probably burn up in the atmosphere

 Large meteorites can explain some mass extinctions and climate changes  The extinction of the dinosaurs is theorized to have happened by a meteorite roughly 10-15km wide

 The moon formed from part of the earth  A large celestial body collided with the primordial earth  The ejected material clumped together  The gravity of the material pulled it into a sphere  The moon began to orbit the Earth

 Do other stars have planets?  Astronomers have discovered more than 200 exoplanets, or planetlike bodies that orbit other stars  Almost all of the exoplanets known have masses similar to Jupiter or Saturn

 Homework: