The Origin of the Solar System Chapter 20 Chapter 20 Notes Quiz Each question is worth 3 points 1. The ___________________________________ proposes that the planets were formed from the disk of gas and dust that surrounded the sun as it formed. 2. _______________________________________ are small, dense, rocky worlds with less atmospheres than the outer planets that lie in the inner solar system. 3. _______________________________________ are large, gaseous, low density worlds that lie in the outer solar system beyond the asteroid belt. 4. A _________________________________ is a meteor in space before it enters Earth’s atmosphere. 5. A _________________________________ is a meteor that has survived its passage through the atmosphere and strikes the ground. 6. What two major elements make up most of the solar nebula? _____________________________________________________________________________________ 7. By the time our solar system reach ed a ___________ (looking for a number) million years of age the formation of the solar system was complete.

The Solar Nebula Hypothesis The solar nebula hypothesis proposes that the planets were formed from the disk of gas and dust that surrounded the sun as it formed As stars form in contracting clouds, they remain surrounded by cocoons of dust and gas, and the rotation of the cloud causes that dust and gas to form a spinning disk around the protostar

The Solar Nebula Hypothesis When the center of the star grows hot enough to ignite nuclear reactions, its surface quickly heats up, becomes more luminous, and blows away the gas and dust cocoon Modern theories suppose that planets form in the rotating disks of gas and dust around young stars

The Solar Nebula Hypothesis ne.org/ViewImage.asp?Cate=Home&SubCate=Introduction&SubCate2=SS00&Img=% If the solar nebula hypothesis is correct, then our Earth and the other planets of the solar system formed billions of years ago as the sun condensed from the interstellar medium. If that is true, then planets form as a by-product of star formation, and most stars should have planets.

Planets Orbiting Other Stars Extra-solar planets is a planet that is orbiting a star other than the sun – Astronomers have found evidence of extra-solar planets by looking for the dust that accompanies planets and by looking for the motions that planets cause as they orbit their stars – Both visible and radio wavelength observations detect dense disks of gas orbiting young stars

Planets Orbiting Other Stars Observations of the Orion Nebula at infrared wavelengths reveal that small dust grains located in disks around young stars are growing, taking the initial steps toward forming planets despite bathing in a flood of radiation from highly luminous stars. – The properties of dust in disks around young stars plays a pivotal role in understanding star formation and determining the origins of planets in our Solar system and in extra-solar planetary systems as well Picture and info copied from: Information matches description in book providing evidence for extra-solar planetshttp://

Two Kinds of Planets Terrestrial planets are small, dense, rocky worlds with less atmospheres than Jovian planets that lie in the inner solar system – Mercury, Venus, Earth, and Mars Jovian planets are large, gaseous, low density worlds that lie in the outer solar system beyond the asteroid belt – Jupiter, Saturn, Uranus, and Neptune

Two Kinds of Planets Terrestrial means “Earthlike” – All are small, rocky planets – Mercury is more like a moon – only 40% larger than our moon and has no atmosphere – Venus is nearly as large as Earth and it has a very thick atmosphere – Mars has a thin atmosphere and its surface is marked by craters and volcanoes

Two Kinds of Planets Jovian planets mean “Jupiter like” – All outer planets are made gas, are much larger than inner planets, have large satellite systems, and have rings Centers of Jupiter and Saturn are believed to be hot cores of heavy elements slightly larger than Earth Uranus and Neptune contain heavy-element cores surrounded by deep layers of icy slush mixed with rocky minerals and dissolved methane and ammonia

Space Debris Sun and planets not only remains of the solar nebula – Three kinds of space debris: Asteroids – small rocky worlds, follow orbits between the orbits of Mars and Jupiter Comets – one of the small, icy bodies that orbit the sun and produce tails of gas and dust when they near the sun Meteoroids – A meteor in space before it enters Earth’s atmosphere – Meteors – A small bit of matter heated by friction to incandescent vapor as it falls into Earth’s atmosphere – Meteorite – A meteor that has survived its passage through the atmosphere and strikes the ground

Ceres Meteor Crater, ARIZONA Meteor Shower Halley’s Comet

The Age of the Solar System We can come up with a pretty good estimate of how old the solar system is by using half-life calculations for different rock samples we have from Earth, the moon, Mars, and meteorites The oldest rocks found on Earth are about 4 billion years old, but Earth’s surface is active and the crust is continually destroyed and reformed, so we know that Earth is at least 4 billion years old

The Age of the Solar System Dating of lunar rocks has showed that the oldest is 4.48 billion years old so the moon has to be at least that old Although no one has yet been to Mars, a few meteorites found on Earth have been identified by their chemical composition as having come from Mars Most of these have ages of only 1.3 billion years, but one has an age of 4.5 billion years making Mars at least that old

The Age of the Solar System Radioactive dating of meteorites yields a range of ages, with the oldest being about 4.6 billion years 4.6 billion year is the most widely accepted age of the solar system Lastly we can look at the sun Astronomers estimate the sun to be about 5 billion years old, but this isn’t a radioactive date because they can’t obtain a sample of solar material It does give us an estimate of the oldest age possible for a solar system though

Characteristics of the Solar System 1)Disk shape of the solar system Orbits in nearly the same plane Common direction of rotation and revolution 2)Two planetary types Terrestrial – inner planets; high density Jovian – outer planets; low density 3)Planetary ring systems for Jupiter, Saturn, Neptune, and Uranus 4)Space debris – asteroids, comets, and meteors Composition Orbits 5)Common ages of about 4.6 billion years from Earth, the moon, Mars, meteorites, and the sun

The Chemical Composition of the Solar Nebula Everything we know about the solar system and star formation suggests that the solar nebula was a fragment of an interstellar gas cloud Such a cloud would have been mostly hydrogen with some helium and tiny traces of the heavier elements Analysis of the solar spectrum shows that the sun is mostly hydrogen, with 25% of its mass being helium and only about 2% being heavier elements The composition revealed in the spectrum is essentially the composition of the gases from which it formed

The Chemical Composition of the Solar Nebula Once a planet has grown to a mass about 15 times Earth it can start to capture gas directly from the solar nebula Jovian planets hit this mass first and started to capture large amount of gas (mostly hydrogen and helium) Jupiter and Saturn grew most rapidly so they captured more of these gases than Neptune and Uranus Terrestrial planets contain very little hydrogen and helium because they couldn’t get large enough to capture these gases from the solar nebula

The Condensation of Solids The inner planets are very dense because the materials in the inner regions of the nebula were dense in nature Inner regions warmer so only materials that had high melting points like metal oxides and pure metals would be found there Metallic grains will be found near the present orbit of Mercury Silicate grains will be found near the present orbit of Earth The outer planets are less dense because the materials in the outer regions of the nebula were less dense in nature Outer regions were cooler so ices of water, methane, and ammonia could condense and were used to create the outer planets Icy grains beyond the present orbit of Jupiter

The Formation of Planetesimals In the development of a planet, three processes operate First, grains of solid matter grow larger, eventually reaching diameters ranging from a few centimeters to kilometers The larger of these objects, called planetesimals, are believed to be the bodies that the second group of processes collects into planets Finally, a third set of processes clears away the solar nebula

The Formation of Planetesimals According to the solar nebula theory, planetary development in the solar nebula began with the growth of dust grains This occurred by two processes: A particle grows by condensation when it adds matter one atom at a time from a surrounding gas Just like the creation of snowflakes by condensation in Earth’s atmosphere The second process is accretion, the sticking together of solid particles Just like building a snowman, roll the ball of snow across the ground and it will pick up more material and get larger

The Growth of Protoplanets Protostars are massive objects destined to become planets If planetesimals collided head on they would be blown totally apart but since they were all moving in same direction they would brush up against one another This action and the action of sticky coatings and electrostatic charges on the surfaces would aid the bodies in getting larger and larger As they grew in size their gravitational force would grow and allow them to pull more and more materials towards them so they could continue to get larger rhig.physics.wayne.edu

The Growth of Protoplanets Once the planet formed, heat began to accumulate in its interior from the decay of short-lived radioactive elements, and this heat eventually melted the planet Next the planet would go through differentiation, which is the separation of material according to density When the planet melted, the heavy metals such as iron and nickel settled to the core, while the lighter silicates floated to the surface to form a low-density crust Most astronomers believe our current atmosphere was created by the baking of rocks on the surface releasing gases sometime after our planet formed

The Growth of Protoplanets Jovian planets formed in about 10 million years – Jupiter and Saturn formed the quickest Terrestrial planets took longer to form – probably about 30 million years – Since they were smaller they couldn’t form of just gas like the Jovian planets so they needed to accrete from planetesimals By the time our solar system reached 100 million years of age the formation of the solar system was complete

Clearing the Nebula Four effects helped clear the nebula – Radiation pressure – MOST IMPORTANT When sun became a luminous object, light streaming from its surface pushed against the particles of the solar nebula - heavy materials weren’t affected, but low-mass specks of dust and individual gas atoms were pushed outward and eventually out of the nebula – Solar wind Flow of ionized hydrogen and other atoms away from the sun’s upper atmosphere that helped push dust and gas out of the nebula

Clearing the Nebula Four effects helped clear the nebula – Planets sweeping up space debris As planets orbited the sun they would continue to grow and pull space debris closer and either would use them to get larger or they would smash into the planet and cause the creation of craters (during period of heavy bombardment) – Ejection of material from the solar system by close encounters with planets If small planetesimals passes close by a planet it can pick up energy from the planet’s gravitational field and it can be slingshot out of the solar system