Solar System CHAPTER 8 - PowerPoint Presentation

Solar System CHAPTER 8 Comparative Planetology II The Origin of Our Solar System

By numbers: 91% 8.9% <0.1%

The Orion Nebula 1500 LY from Earth

Young Stars in the Orion Nebula

Antares

Dust Grain from Space collected by high-flying airplane

Relative Abundances of Elements in the Milky Way

Radioactive Dating: Measuring the age of the Solar System

Radioactive Decay U-238 → Pb-206

Question Ar 40 is an inert gas and therefore can’t be contained in hot magma that flows out of volcanoes. Ancient lava flows have been dated using the radioactive decay of K 40 into Ar 40 whose ½ - life is1.25 Gyr. A solidified rock of basaltic magma is found on Earth that contains 1 K 40 atom for every 7 Ar 40 atoms. When did this rock solidify? 1.25 Gya 2.50 Gya 3.75 Gya 5.00 Gya No more than 6000 years ago (3 half – lives!)

Age of Solar System – 4.56 Billion Years

Formation

Temperature Distribution in Early Solar Nebula

Ices ( H 2 O, CH 4 , NH 3 ) condense beyond the frost lineIces are 20 times more abundant than rocks&metals!

Question Which physical parameter most determined the early evolution of the planetary system and dictated the characteristics of the planets that eventually formed? overall speed of rotation of the nebula temperature distribution within the nebula density of hydrogen gas in the nebula the total amount of radioactive material within the nebula position of the system relative to nearby stars

…or by core accretion first .

Accretion of Terrestrial Planets

Solar Nebula Model

Core Accretion: Large icy core forms first – followed by gas accretion Disk Instability: Dense regions in gaseous outer disk collapse first – followed by attraction of ices Formation of Jovian Planets

Began as icy fragments beyond Jupiter Flung out into outer reaches of solar system Kuiper Belt

Image of planets forming in HL Tau (10 6 yrs old) 450 LY away Image captured by ESA Alma Atacama mm/sub-mm array Computer Simulation

Question The theory that the Sun and the planets formed out of a massive, rotating nebular cloud of gas and dust is supported by the fact that _____. planets and moons with surfaces not modified by geological processes are covered with craters whose ages mostly exceed 4 billion years the planets all revolve around the Sun in the same direction orbits of planets and their moons all lie in almost the same plane the solar system is divided into two regions occupied by either terrestrial or Jovian planets. The dividing line is where it was cold enough in the early solar nebula for ices to condense … all of the above

Finding Extrasolar Planets

The Radial Velocity Method

Extrasolar Planet Transiting its Parent Star

Even Better – Directly Image the Extrasolar Planet!

Question Until the launch of the Kepler telescope, the ‘Doppler Shift’ technique, in which a parent star’s absorption spectrum is observed to ‘wobble’ over a period of several days, was the one that had been used to find the majority of the extrasolar planets discovered so far. Why is this? Most extrasolar planets are huge. Most extrasolar planets orbit close to their parent star. It’s easy to obtain a star’s absorption spectrum. Most huge extrasolar planets have orbital periods of only a few days. Doppler shifts large enough to be detectable with current technology can only be caused by planets that are large and orbit very close to their parent star.

Key IdeasModels of Solar System Formation: The most successful model of the origin of the solar system is called the nebular hypothesis. According to this hypothesis, the solar system formed from a cloud of interstellar material called the solar nebula. This occurred 4.56 billion years ago (as determined by radioactive dating).

Key IdeasThe Solar Nebula and Its Evolution: The chemical composition of the solar nebula, by mass, was 98% hydrogen and helium (elements that formed shortly after the beginning of the universe) and 2% heavier elements (produced much later in the centers of stars, and cast into space when the stars died). The heavier elements were in the form of ice and dust particles.

Key IdeasFormation of the Planets and Sun: The terrestrial planets, the Jovian planets, and the Sun followed different pathways to formation. The four terrestrial planets formed through the accretion of dust particles into planetesimals, then into larger protoplanets.In the core accretion model, the four Jovian planets began as ice and rocky, metal protoplanetary cores, similar in character to the terrestrial planets…but much larger because of the addition of the much more abundant ices. Gas then accreted onto these cores in a runaway fashion.

Key IdeasIn the alternative disk instability model, the Jovian planets formed directly from the gases of the solar nebula. In this model the cores formed from planetesimals falling into the planets.The Sun formed by gravitational contraction of the center of the nebula. After about 108 years, temperatures at the protosun’s center became high enough to ignite nuclear reactions that convert hydrogen into helium, thus forming a true star.

Key IdeasExtrasolar Planets: Astronomers have discovered planets orbiting other stars. Most of these planets are detected by the “wobble” of the stars around which they orbit.A small but growing number of extrasolar planets have been discovered by the transit method, by microlensing, and direct imaging.Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system.