Chapter 19 Origin of the Solar System

Transcription

1 Foundations of Astronomy 13e Seeds Phys1411 Introductory Astronomy Instructor: Dr. Goderya Foundations of Astronomy 13e Seeds Chapter 19 Origin of the Solar System Topics for this Class I. Survey of Solar System A. Revolution and Rotation B. Two Kinds of Planet C. Cosmic Debris D. Age of the Solar System II. Origins of Solar System A. Early Hypotheses B. The Solar Nebular Theory Topics for next Class III. Building Planets A. Chemical Composition of the Solar Nebula B. Condensation of Solids C. Formation of Planetesimals D. Growth of Protoplanets E. Jovian Problem F. Clearing the Nebula IV. Planets Orbiting Other Stars IV. Planet forming disks V. Observing extrasolar Planets VI. The Kepler Planet-Finding Mission Survey of the Solar System Planets in the Our Solar System All the planets orbit in the same direction, in one plane, in approximately circular orbits. Comets, in contrast, normally have very eccentric orbits that are often inclined to the plane of the planets orbits. These are all clues to how the Solar System formed. The planets are shown here roughly 2000 times larger than their true diameters relative to the sizes of their orbits. The Solar System is flat and disk-shaped wikipedia 1

2 Revolution, Rotation and Inclination of Planets A planet revolves around the Sun but rotates on its own axis Orbit is counterclockwise and rotation on axis is counterclockwise Exceptions: Venus and Uranus rotate in different directions Universetoday com Two Kinds of Planets: Terrestrial and Jovian Planets The two kinds of planets are distinguished by their location Craters are common on most planets The two groups of planets are also distinguished by properties such as number of moons and presence or absence of rings Terrestrial Planets Inner four planets are small, dense, rocky with little or no atmosphere Jovian Planets Outer four planets: Are large, lowdensity worlds with thick atmospheres and liquid or ice interiors Possess rings and extensive satellite systems Slideshare.net 2

3 ClassAction: Astronomy Education at the University of Nebraska-Lincoln Web Site ( Cosmic Debris - Asteroids Common Misconception (a) Over a period of three weeks, the NEAR spacecraft approached the asteroid Eros and recorded a series of images arranged here in an entertaining pattern showing the irregular shape and 5 -hour rotation period of the asteroid. Eros is 34 km ( 21 mi) long. (b) This close-up of the surface of Eros shows an area about 11 km (7 mi) from top to bottom. Misconception: Asteroids are the remains of a planet that broke apart Truths: Planets are held together very tightly by their gravity and do not break apart Asteroids are debris left over from the failure of a planet to form at a distance of about 3 AU from the Sun Cosmic Debris - Comets Where Do Comets Come From? Kuiper Belt objects (KBOs): objects beyond Neptune Comets: icy nucleus and long dusty tail as it nears the Sun A comet may remain visible in the sky for weeks as it passes through the inner Solar System. Although comets are actually moving rapidly along their orbits, they are so distant that, on any particular evening, a comet seems to hang motionless in the sky relative to the background constellations. Comet Hyakutake is shown here near Polaris in Kuiper Belt Objects Beyond the orbit of Neptune Short Period comets Like Halley Contains millions of comet Oort Cloud Beyond the orbit of Pluto Most comets come from Oort cloud Contains trillions of comets cefns.nau.edu 3

4 Cosmic Debris - Meteoroids: objects weighing < 1 gram are often found falling into a planet s atmosphere A meteor is a sudden streak of glowing gases produced by a bit of material falling into Earth s atmosphere. Friction with the air vaporizes the material about 80 km (50 mi) above Earth s surface. This meteor is seen against the background of part of the Milky Way. Comparing Comets, Asteroids and Meteoroids Feature Comets Asteroids Meteoroids Origin Kuiper Belt and Oort Cloud Size 750 meters 20 kilometers Between Mars and Jupiter Most are less than 1 km, a few several hundred kilometers Debris from passing comets and asteroids Lot smaller than comets and asteroids Density Less than 1 g/cm3 Between 2 5 g/cm3 Between 3 4 g/cm3 Denser than most terrestrial rocks Composition Mainly Ice, and dust Rock Rock and Dust Radioactivity ClassAction: Astronomy Education at the University of Nebraska-Lincoln Web Site ( Radioactivity refers to particles or radiation which is emitted from unstable isotope or nuclei of an atom. There are three types of radiation, alpha, beta and gamma. In a radioactive process the parent atoms decays into another element called the daughter. The number of atoms left after a specific amount of time to decay is given by N o is the initial number of atoms and t is time and λ is the decay constant. The number of decays per second is called the activity of the sample. The speed at which the isotope decay is called the half life or the time it takes for half of the atoms to decay. Half life is calculated by 2 Age of the Solar System Creation of Solar System: Early Hypotheses Radioactive dating: measure half-life of radioactive substance in rocks and meteorites Solar System is 4.6 billion years old The radioactive atoms (red) in a mineral sample decay into daughter atoms (blue). Half the radioactive atoms are left after one half-life, a fourth after two half-lives, and eighth after three half-lives, and so on. Descartes: Evolutionary hypothesis Solar system formed gradually from a vortex of matter to make the sun and planets Ic.galegroup.com 4

5 Creation of Solar System: Early Hypotheses Buffon: Catastrophic hypothesis A comet pulled matter out of the solar system to build planets Later version: Passing Star hypothesis A star pulled matter out of the solar system to build planets Planets should be closer to the sun than they actually are Abyss.uoregon.edu Slideshare.net Creation of Solar System: Early Hypotheses Laplace s and Kent nebular hypothesis cannot explain the angular momentum of the sun. This is known as the angular momentum problem in which the sun should have a high angular momentum contrary to what is observed. Modern View All matter is made from H and He present from the time of big bang Atoms heavier than He (Metals) are formed in nuclear fusion reactions in Stars When stars explode the ejected matter forms a interstellar cloud of gas and dust The Sun and planets are formed in the interstellar cloud The Solar Nebula Theory Additional Videos for Review The solar nebula theory implies that the planets formed along with the Sun. 1. A rotating cloud of gas contracts and flattens 2.To form a thin disk of gas and dust around the forming Sun at the center. 3.Planets grow from gas and dust in the disk and are left behind when the disk clears minutes 50 minutes 5

6 Extrasolar (exoplanets) Planets These are planets around other stars. Astronomers have detected many thousands of planets There are 5 basic method of detecting exoplanet Direct Imaging Astrometry Radial Velocity (RV) measurements Gravitational lensing Transit Method Direct Imaging Method Planetary systems outside of our own do exist Most are like Jupiter, but planets like Earth have recently been found Image of a Jovian-size planet orbiting 9 AU from the star Beta Pictoris. In both images, the central circular blank region represents a combination of hardware and software masks implemented to block light from the central stars that are much brighter than the planets. Another Example Astrometry Four planets around HR 7899 observed with Palomar Telescope Astronomers can detect a planet orbiting another star by watching how the star moves as the planet tugs on it Astronomynotes.com Astrometry a) A person walking a lively dog is tugged off course by the dog. b) The star 51 Pegasi is pulled back and forth by the gravity of the planet that orbits it every 4.2 days. The wobble is detectable in precision observations of the star s Doppler shift. Astrometry a) A person walking multiple dogs has complicated motion. b) Doppler shifts of the star Upsilon Andromeda show the combined effects of at least four planets orbiting it. The influence of its shortest-period planet has been removed in this graph to reveal more clearly the orbital influences of the other three planets. 6

7 Radial Velocity Method Gravitational Microlensing Astronomers can detect a planet orbiting another star by using Doppler Shift and Obtaining Radial Velocity culturesciencesphysique.ens-lyon.fr NASA/ESA/STScI Transit Method Orbit of Extrasolar Planet and Inclination Majority of the extrasolar planets discovered so far are by using the radial velocity and transit method. Astronomers can detect a planet orbiting another star by looking for dips in light curve To see Transit or radial velocity the inclination of the orbit should be less then 90 degrees During Transit or occultation the radial velocity of the plane is approaching zero because we cannot detect Doppler shift. exoplanetes-lombards.eklablog.com Planet-Forming Disks Evidence of Dust Disks Dark bands (indicated by arrows) are edge-on disks of gas and dust around young stars seen in Hubble Space Telescope near-infrared images. Planets may eventually form in these disks. These systems are so young that material is still falling inward and being illuminated by light from the stars. 7

8 Kepler Mission The Kepler Planet-Finding Mission Kepler space telescope uses transit method to detect extrasolar planets Transit light curve of the first confirmed extrasolar Terrestrial planet, Kepler 10-b. The planet has an orbital period of 0.84 day. The depth of the transit dip indicates that the planet has 1.4 times the diameter of Earth. Spectroscopic measurements with ground-based telescopes of the parent star s radial velocity variation give a mass for the planet of 4.6 times Earth s mass. The planet s diameter and mass yield a density of 8.8 g/cm 3, higher than Earth s, indicating a mostly metallic composition. The Kepler Planet-Finding Mission (cont d.) confirmed extrasolar planets discovered Majority are hot Jupiters and hot Neptunes but about 150 are considered hot Earths Kepler-186f is the first confirmed discovery of Earth-size, Earth-temperature extrasolar planet (2014) Early this semester 3 more Earth like planes were discovered around another star Observing Extrasolar Planets Extrasolar planets discovered so far are massive with short orbital periods Contradiction to solar nebula theory: The mystery of hot Jupiter's But in our solar system Jupiter is far from the sun and is much cooler than Jupiter like planets that our found to be closer to their sun and much hotter. Eccentric orbits But in our solar system all planets are nearly circular in orbit Orbits with large angles to equators of parent star But in our solar system all planets orbit in a plane Acknowledgment The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. 8