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Transcript
The Origin of Our Solar System Early Hypotheses 1 Objectives • SWBAT evaluate varying hypotheses and their evidence about the origin of the solar system. • SWBAT compare, and contrast hypotheses about the origin of our solar system. 2 Early Hypotheses - Examples • René Descartes (Early 17th century) – Created first recorded physical theory. – Did not recognize gravitation as the universe’s central force. – Believed force was exerted by contact betwn physical entities and the universe was filled with vortices of “whirling invisible particles.” – Posited that the sun and planets formed when a large vortex contracted and condensed. 3 Early Hypotheses - Examples • Louis de Buffon (mid to late 17th century) was a French naturalist. – Proposed that the planets formed when a comet collided with the sun and pulled matter out of it. – Buffon knew nothing of the actual size of a comet; however, later astronomers took his idea and replaced the comet with a passing star. – Matter ripped from the two stars condensed to form planets. 4 Catastrophic V. Evolutionary (these ideas are found throughout science) • Descartes’ theory – is an “evolutionary” type theory. – An evolutionary theory involves gradual processes to produce the sun and planets. – If an evolutionary perspective were correct, and the origin of planets, solar systems, and galaxies were through gradual, common, process, then stars and planets would be very common. 5 Catastrophic V. Evolutionary • Buffon’s theory depends on highly improbable, sudden events. – If a catastrophic theory were true, then planetary systems should be very rare. • The catastrophic versus evolutionary debate has mostly been settled. • Scientists have mostly sided with the gradualist perspective; however, catastrophism does play a real role and should not be dismissed. 6 Evolutionary Processes Are Favored • The modern theory for the origin of the planets, which is based on large amounts of data, is without a doubt evolutionary. • The modern theory began to form in the late 17th early 18th centuries when Pierre-Simon de Laplace combined Decartes’ vortex idea with Newton’s laws of gravity. 7 Laplace’s Nebular theory • Many of science’s greatest advances come when there is a synthesis of two seemingly different disciplines (astronomy and physics in this case. Laplace posited that vortices had been acted on by gravity – applying Newton’s laws. Gravitational forces pulled on the vortices and flattened them out into a disk. The center of the vortex became the sun. 8 Nebular theory Continued • Disks grew smaller as gravity acted on them. – In order to maintain angular momentum the sun, the source of the spin, and the resulting disks had to spin faster: Angular momentum = moment of inertia x angular velocity. The increased “spin” was necessary to keep the evolving disk rotating. 9 Nebular theory Continued • When our cloud of spinning matter was spinning as “fast as it could,” the disk began to shed layers – leaving behind rings of matter. This is a painting of the early solar system, according to Laplace, from NASA’s website. 10 Nebular theory Continued • As the cloud spun, it created many rings. – The rings would become the newborn planets orbiting a new sun at the center of what was the cloud of gas (which remember, is matter). • As with most hypotheses in science, this one was a very good try but the evidence did not support it. 11 Nebular theory Continued • The theory depended on the sun having most of the angular momentum in the solar system. – Angular momentum (re-stated in easier to understand form): the tendency of a rotating object to continue to rotate. – In fact, the sun rotates relatively slowly – having little angular momentum. – The planets rotate much faster and have greater angular momentum. 12 Nebular theory Continued • The Nebular theory could not adequately explain the angular momentum problem (sun low, planets high). • Therefore it was rejected, however, it was absolutely key because of its incorporation of Newton’s laws of motion. • It was the first “modern” theory. • In the 1940s, the Solar Nebula theory was proposed. 13 Solar Nebula Theory (SNT) • Proposes that the planets, including Earth, formed in a rotating disk of gas and dust that surrounded the sun as it, the sun, formed. Laplace’s nebular theory included a disk but depended on rings of matter left behind by disk contraction. He did not take into account how gas and dust behave in such a disk. In the SNT, the planets grew within the disk by carefully described physical processes – an evolutionary process (called uniformitarianism in geology. 14 Solar Nebula Theory (SNT) • Disks of gas and dust are common around young stars. • Modern astronomical tools can image the disks directly and evidence is strong that our own planetary system formed in such a disk shaped cloud. • So, evidence comes from direct observation as well as the laws of physics and chemistry – and now biology and geology. 15 Solar Nebula Theory (SNT) • If planet formation is a natural part of star formation, from the disks of gas and dust, then most stars should have planets orbiting them. 16 This is a borrowed slide 17 Neil deGrasse Tyson, from Nova Now • http://www.pbs.org/wgbh/nova/space/origins -solar-system.html 18