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© Cengage Learning 2016

Foundations of Astronomy | 13eSeeds


Phys1411 – Introductory AstronomyInstructor: Dr. Goderya


Foundations of Astronomy | 13eSeeds


Chapter 19

Origin of the Solar System


I. Survey of Solar SystemA. Revolution and RotationB. Two Kinds of PlanetC. Cosmic DebrisD. Age of the Solar System

II. Origins of Solar SystemA. Early HypothesesB. The Solar Nebular Theory

Topics for this Class


Topics for next ClassIII. Building Planets

A. Chemical Composition of the Solar NebulaB. Condensation of SolidsC. Formation of planetesimalsD. Growth of ProtoplanetsE. Jovian ProblemF. Clearing the Nebula

IV. Planets Orbiting Other StarsIV. Planet forming disksV. Observing extrasolar PlanetsVI. The Kepler Planet-Finding Mission


Survey of the 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

Planets in the Our Solar System

wikipedia

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Universetoday com

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


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, low-

density worlds with thick atmospheres and liquid or ice interiors

– Possess rings and extensive satellite systems

Slideshare.net

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ClassAction: Astronomy Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu© Cengage Learning 2016

Cosmic Debris - Asteroids

(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.


Common Misconception

• 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


• 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 1996.

Cosmic Debris - Comets


• 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

Where Do Comets Come From?

cefns.nau.edu© Cengage Learning 2016

Meteoroids: objects weighing < 1 gram are often found falling into a planet’s atmosphere

Cosmic Debris -

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.

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Comparing Comets, Asteroids and Meteoroids

Feature Comets Asteroids Meteoroids

Origin Kuiper Belt and Oort Cloud

Between Mars and Jupiter

Debris from passing comets and asteroids

Size 750 meters – 20 kilometers

Most are less than 1 km, a few several hundred kilometers

Lot smaller than comets and asteroids

Density Less than 1 g/cm3 Between 2‐5 g/cm3 Between 3‐4 g/cm3Denser than most terrestrial rocks

Composition Mainly Ice, and dust Rock Rock and Dust

ClassAction: Astronomy Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu

• 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

• No 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

Radioactivity


Radioactive dating: measure half-life of radioactive substance in rocks and meteorites

Solar System is 4.6 billion years old

Age of the Solar System

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

Creation of Solar System: Early Hypotheses

Ic.galegroup.com

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

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1. Solar system was formed from a giant ball of gas.

2. As the gas cloud expanded and cooled it lost mass, spinning and centrifugal force caused a disk shape.

3. The center of the disk grew in mass attracting more matter due to gravitational pull.

4. The outer region broke into several rings

5. The rings finally condense into planets while the center became hot enough to make the Sun.

Creation of Solar System: Kant an Laplace

PMF IAS

Kant and Laplace’s nebular hypothesis could not explain the low angular momentum of the sun that we know of today.


PMF IAS


• 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

Modern View


The Solar Nebula Theory

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.

https://www.youtube.com/watch?v=PL3YNQK960Y

Additional Videos for Review

https://www.youtube.com/watch?v=gzF03Nls9QM

https://www.youtube.com/watch?v=RR7y_cP5Z0Y

50 minutes

12 minutes


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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.

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