AST 111 Lecture 04 Birth And Properties Of Our Solar System © 2017 Pearson Education, Inc.

Learning Goals: What are the important categories for objects in our solar system? What features of our solar system provide clues to how it formed? How does the nebular theory account for the features (Physics Essentials 02)? How do we gather information about our solar system (Physics Essentials 03)? © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Sun and planets to scale © 2017 Pearson Education, Inc.

One star: the brightest and largest single object in our solar system with over 99.8% of solar system's mass made mostly of H/He plasma (ionized gas) © 2017 Pearson Education, Inc. What are the important categories for objects in our solar system?

Four inner (near the Sun), terrestrial planets: Rocky surfaces © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Four outer, jovian (gas giants like Jupiter) planets: no known solid surface consist mostly of H/He many moons orbit each © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Millions of known asteroids: Small and made of rock and metal Most known asteroids make up the asteroid belt between the orbits of Mars and Jupiter © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Thousands of known comets: Small and made of rock but consisting of much ice Comets are thought to originate from the Kuiper Belt or hypothetical Oort Cloud. © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Numerous dwarf planets: spherical objects that have not yet cleared their orbital neighborhoods of objects of similar size found in the asteroid belt and Kuiper belt © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Numerous centaurs: objects with unstable, exaggerated orbits among the gas giants disturbed comets or dwarf planets from Kuiper Belt © 2017 Pearson Education, Inc.

What are the important categories for objects in our solar system? Hundreds of known moons: orbit larger objects small and made of rock and metal with many consisting of ice often captured by planets only three of the moons in the inner solar system Mercury and Venus have no moons © 2017 Pearson Education, Inc.

Focus on patterns common to multiple worlds instead of individual facts specific to a particular world. Those patterns provide insights that help us learn more about our solar system’s formation. Our solar system’s formation reveals more about Earth’s formation and ultimately us. © 2017 Pearson Education, Inc. What features of our solar system provide clues to how it formed?

All large bodies in the solar system orbit in the same direction and in nearly the same plane. Most also rotate in that direction. © 2017 Pearson Education, Inc. What features of our solar system provide clues to how it formed?

Terrestrial planets are rocky, relatively small, and close to the Sun. Jovian planets are gaseous, larger, and farther from the Sun. © 2017 Pearson Education, Inc. What features of our solar system provide clues to how it formed?

Many rocky asteroids and more distant icy comets populate the solar system. © 2017 Pearson Education, Inc. What features of our solar system provide clues to how it formed?

Several exceptions to the normal patterns need to be explained. © 2017 Pearson Education, Inc. What features of our solar system provide clues to how it formed?

1.Patterns of motion of the large bodies Orbit in same direction and plane 2.Existence of two types of planets Terrestrial and jovian 3.Existence of differing smaller bodies Asteroids and comets 4.Notable exceptions to usual patterns Rotation of Uranus, Earth's Moon, etc. © 2017 Pearson Education, Inc. What features of our solar system provide clues to how it formed?

The nebular hypothesis states that our solar system formed from the gravitational collapse of a giant interstellar gas cloud—the solar nebula. Kant and Laplace proposed the nebular hypothesis over two centuries ago. The nebular theory includes the nebular hypothesis as well as other consequential hypotheses and relevant physical laws. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Physics Essentials 02 A useful concept for Astronomy is angular momentum (α), which can be regarded as ability to remain rotating and depends on mass, speed, and distribution of mass: Law Of Conservation Of Angular Momentum: The angular momentum of an isolated system does not change. Speed changes if the mass distribution changes. © 2017 Pearson Education, Inc.

Physics Essentials 02 For an ice skater, notice that if distribution of mass decreases, speed must increase … … to keep the angular momentum balanced and unchanged. © 2017 Pearson Education, Inc. m v r = m v r

Physics Essentials 02 Another useful concept is energy (E), which can be regarded as a means of quantifying conditions or states. So there are many types of energies. An important aspect of energy is possessiveness so the energy possessed by a particle can be transferred to another particle or … … transformed if its condition changes. Law Of Conservation Of Energy: The total energy of a system does not change if there are no processes to add or remove energy. © 2017 Pearson Education, Inc.

Physics Essentials 02 Some energies are: kinetic energy radiative energy thermal energy potential energies due to gravity, electricity, atomic or nuclear states, etc. When energies transform, amounts are accounted for by energy conservation. © 2017 Pearson Education, Inc. potential energies (rest energies)

Physics Essentials 02 Thermal energy is energy of random, microscopic motions of particles. depends on temperature and number of particles in a volume. Temperature (T) can be regarded as an indication of random microscopic motions. © 2017 Pearson Education, Inc.

Rotation of the cloud from which our solar system must have formed, increased as the cloud contracted. just like spinning skaters pulling in their arms angular momentum conservation law As particles collide and clump, the average resulting direction of the clumps matches the average direction of the original cloud rotation. the cloud flattens into a disk How does the nebular theory account for the features?

We see stars beginning to form in distant giant gas clouds, lending support to the nebular theory. These systems are still too young to develop disks. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

As planets begin to form in disks, they revolve in the same plane and in the same direction (1). © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

© 2017 Pearson Education, Inc. How does the nebular theory account for the features? Conservation of energy accounts for energy transformation in a contracting gas cloud.

With a hot interior and a cold exterior, there will be a frost line: a boundary beyond which it is cold enough for hydrogen compounds to form ices. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Inside the frost line, ices cannot condense, but rock and metal can condense. Planetesimals of rock and metal build up as these particles collide, and gravity eventually assembles planetesimals into planets. a process called accretion. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

A combination of light and the solar wind (outflowing, high-energy particles from the Sun) blew away non-condensed gases in the inner solar system. … preventing formation of gas giants in the inner solar system when it cooled … … leaving small, rocky, terrestrial planets. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Beyond the frost line, ices can condense … … and there is a LOT of material to form ices … … allowing formation of larger planetesimals. Gravity of larger planetesimals can hold onto surrounding H and He gases and accrete more. Giant jovian planets generate miniature disks permitting moon formation (2). © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Leftover planetesimals from the disk … … inside the frost line remain as rocky asteroids. … outside the frost line remain as icy comets (3). © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

So many leftover planetesimals should leave their mark in collisions with larger objects. We observe the signs of this Late Heavy Bombardment as numerous craters on the Moon and other bodies. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Impacts (especially giant ones) might also explain several exceptions to the common patterns (4): … such as the nearly horizontal rotation axis of Uranus. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

© 2017 Pearson Education, Inc. A colossal collision is also currently the best explanation for Earth’s unusually large moon. How does the nebular theory account for the features?

Unusual moons of some planets may be captured planetesimals … … like these two moons of Mars (the only other moons in the inner solar system). © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Another exception is the rotation of our Sun, which is much slower than that predicted by conservation of momentum. A young Sun probably rotated very fast. Friction between solar magnetic field and a young gaseous disk can slow rotation. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Which of these facts is NOT explained by the nebular theory? A.There are two main types of planets: terrestrial and jovian. B.Planets orbit in same direction and plane. C.Existence of asteroids and comets. D.Number of planets of each type (four terrestrial and four jovian). © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

Which of these facts is NOT explained by the nebular theory? A.There are two main types of planets: terrestrial and jovian. B.Planets orbit in same direction and plane. C.Existence of asteroids and comets. D.Number of planets of each type (four terrestrial and four jovian). © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

The close encounter hypothesis was a rival idea proposed that the planets formed from debris torn off the Sun by a close encounter with another star. That hypothesis could not explain the different categories of planets near or far and could not account for the overwhelmingly common motions of solar system bodies. © 2017 Pearson Education, Inc. How does the nebular theory account for the features?

How do we gather information about our solar system? Light is the only means of getting direct information about our universe outside of our solar system. But inside, we are close enough to send probes. A flyby mission flies by a planet just once. cheaper than other missions but less time to gather data © 2017 Pearson Education, Inc.

Orbiters go into orbit around another world. More time to gather data but cannot obtain detailed information about world's surface. © 2017 Pearson Education, Inc. How do we gather information about our solar system?

Landers land on the surface of another world. explore surface in detail either in place or roving © 2017 Pearson Education, Inc. How do we gather information about our solar system?

Sample return missions land on the surface of another world and gather samples. Spacecraft designed to blast off from other world and return to Earth. Apollo missions to Moon are one example. Hyabusa to an asteroid is another. Analysis of radioactive isotopes in samples permits determination of formation age of the source. © 2017 Pearson Education, Inc. How do we gather information about our solar system?

Physics Essentials 03 Atoms are the smallest systems that make up all matter and consist of: protons and neutrons in the central nucleus electrons surrounding the central nucleus Elements classify atoms identifying them by their number of protons. © 2017 Pearson Education, Inc.

Physics Essentials 03 Isotopes are elements with differing numbers of neutrons. © 2017 Pearson Education, Inc.

Physics Essentials 03 © 2017 Pearson Education, Inc. Some radioactive isotopes change into other nuclei. Decay of each nucleus is random but with a large enough sample, there is a precise time for half the nuclei in the sample to decay (half life).

Suppose you find a rock originally made of potassium-40, half of which decays into argon-40 every 1.25 billion years. You open the rock and find 15 atoms of argon-40 for every atom of potassium-40. How long ago did the rock form? A.1.25 billion years ago B.2.5 billion years ago C.3.75 billion years ago D.5 billion years ago © 2017 Pearson Education, Inc. How do we gather information about our solar system?

Suppose you find a rock originally made of potassium-40, half of which decays into argon-40 every 1.25 billion years. You open the rock and find 15 atoms of argon-40 for every atom of potassium-40. How long ago did the rock form? A.1.25 billion years ago B.2.5 billion years ago C.3.75 billion years ago D.5 billion years ago © 2017 Pearson Education, Inc. How do we gather information about our solar system?

© 2017 Pearson Education, Inc. Radiometric dating demonstrates that oldest moon rocks are 4.4 billion years old. Oldest meteorites are 4.55 billion years old. Planets (including Earth) probably formed 4.5 billion years ago. supported by radiometric dating Earth rocks How do we gather information about our solar system?