Chapter 12 The Origin of the Solar System

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• Chapter 12The Origin of the Solar System

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• The solar system is our home in the universe.
• As intelligent species, we have the right and the
  responsibility to wonder what we are and where we
  live, to study the universe..

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• Humans have inhabited the solar system for at
  least a million years. However, only within the
  last
• 2400 years have we begun to realize that we live
  in a cosmos and a planetary system
• 400 years have we begun to understand the details
  of the true heliocentric architecture of our
  solar system
• 300 years have understood its mechanics
• 200 years have we started to make detailed
  scientific models of its origin
• 100 years have sensed that its chaotic yet
  stable, and where it is located in a Galaxy

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• Humans have inhabited the solar system for at
  least a million years. However, only within the
  last
• 90 years have we completed the Copernican
  revolution Harlow Shapley removed the Sun from
  the center of the Galaxy, and Edwin Hubble the
  Galaxy from the center of the Universe
• 50 years have we figured out how the sun works
  and how the stars produced the atoms in our
  bodies

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• Humans have inhabited the solar system for at
  least a million years. However, only within the
  last
• 30 years have we begun to observe understand
  details of star formation such as protostellar
  disks and their relevance to our origins
• 20 years have we begun to observe durect evidence
  for planetary systems other than our own
• 10 years have we placed our system in a wider
  context and compared it with hundreds of newly
  discovered extrasolar systems
• and started filling the gaps in our theories of
  the origins

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The Great Chain of Origins

• You are linked through a great chain of origins
  that leads backward through time to the first
  instant when the universe began 13.7 billion
  years ago.
• The gradual discovery of the links in that chain
  is one of the most exciting adventures of the
  human intellect.

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The Great Chain of Origins

• In the course ASTA02 (next semester) you will
  have an opportunity to study some of that story
  in some detail, including
• The origin of the universe in the big bang,
• The formation of galaxies,
• The origin of stars, and
• The production of the chemical elements.
• Here, you will explore
  the origin
• of planets.

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The History of the Atoms in Your Body

• By the time the universe was three minutes old,
  the protons, neutrons, and electrons now in your
  body had come into existence.
• You are made of very old matter (13.7 Gyr old)

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The History of the Atoms in Your Body

• Although those particles formed quickly, they
  were not linked together to form the atoms that
  are common today.
• Most of the matter was hydrogen (almost 75)
• and about 25 was helium.
• Very few (lt 1) of the heavier atoms were made in
  the big bang.
• The big bang also formed the so-called dark
  matter, which permeates the planetary systems at
  very low density, but has very little interaction
  with them.

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The History of the Atoms in Your Body

• Although your body does not contain helium, it
  does contain many of those ancient hydrogen atoms
  that have remained unchanged since the universe
  began.
• We are made mostly of water, and water is made
  mostly of hydrogen (counting the atoms), and of
  oxygen (which dominates our mass)

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The History of the Atoms in Your Body

• During the first few hundred million years after
  the big bang, matter collected to form galaxies
  containing billions of stars. Our Galaxy was
  built 8.8 Gyr ago (so-called thin disk)
• recent galaxy
  formation also
• occurs
• nuclear reactions inside stars combine low-mass
  atoms, such as hydrogen, to make heavier atoms.

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The History of the Atoms in Your Body

• Generation of stars combined the original
  particles, fusing them into atoms such as carbon,
  nitrogen, and oxygen CNO
• Those are common atoms in your body.
• Even the calcium atoms in your bones were
  assembled inside stars.

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The History of the Atoms in Your Body

• Most of the iron in your body was produced by
• Carbon fusion in the explosions of stars called
  supernovae, and
• Decay of radioactive atoms in the expanding
  matter ejected by supernovae.

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The History of the Atoms in Your Body

• Atoms heavier than iron, such as iodine, were
  created by rapid nuclear reactions that can occur
  only during supernova explosions.

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The History of the Atoms in Your Body

• Elements uncommon enough to be expensive gold,
  silver, and platinum in the jewellery that humans
  wear also were produced during the violent
  deaths of rare, massive stars.

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The History of the Atoms in Your Body

• Our galaxy contains at least 100 billion stars,
  of which the Sun is one.
• The Sun formed from a cloud of gas and dust about
  4.56 billion years ago (4.56 Gyr ago).
• The atoms in your body were part of that cloud,
  and previously part of another cloud that formed
  an earlier star which no longer exists
• You are stardust, reprocessed many times over the
  13.7 Gyr, enriched in heavy elements inside stars
  and in exploding stars.

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The History of the Atoms in Your Body

• How the Sun took shape, how the cloud gave birth
  to the planets, and how the atoms in your body
  found their way onto Earth and into you is the
  story of this chapter.

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The History of the Atoms in Your Body

• As you explore the origin of our solar system,
  you should keep in mind the great chain of
  origins that created the atoms.
• As the geologist Preston Cloud remarked, Stars
  have died that we might live.

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The Origin of the Solar System

• Astronomers have a theory for the origin of our
  solar system that is consistent both with
  observations of the solar system and with
  observations of star formation.
• Now, after the discovery of extrasolar planets
  they are refining the details of the theories of
  formation that would explain both our and other
  planetary systems.

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The Origin of the Solar System

• The solar nebula theory supposes that planets
  form in the rotating disks of gas and dust around
  young stars.

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The Origin of the Solar System

• Our own planetary system formed in such a
  disk-shaped cloud around the Sun.
• When the Sun became luminous enough, the
  remaining gas and dust were blown away into space
  by the solar wind (a stream of charged particles
  from the Sun), and UV (ultraviolet) radiation,
  leaving the planets orbiting the Sun.

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The Origin of the Solar System early concepts

• According to the solar nebula hypothesis, Earth
  and the other planets of the solar system formed
  4.56 billions of years ago as the Sun condensed
  from the interstellar medium.
• Kant-Laplace nebula
• Immanuel Kant (1724-1804) -
  dust stones
• Pierre-Simon de Laplace (1749-1824) - gas
  rings

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Kant and Laplace nebular models
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The Origin of the Solar System

• The theory predicts that most stars should have
  planets because planet formation is a natural
  part of star formation.
• Therefore, planets should be very common inthe
  universe probably more common than stars.

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The Origin of the Solar System

• These young stars form at the centre of a
  rotating cloud of gas and dust that starts to
  contract due to gravity.
• Collisions between particles in the rotating
  cloud tend to flatten the cloud into a disk
  shape.
• In addition, as the cloud shrinks it spins faster
  due to the conservation of angular momentum.
• Most of the material in the spinning disk forms a
  star in the centre, while the remaining material
  forms the planets and other bodies such as
  asteroids and comets.

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The Origin of the Solar System

• There is clear evidence that disks of gas and
  dust are common around young stars.
• The idea is so comprehensive and explains so many
  observations that it can be considered to have
  graduated from being just a hypothesis to being
  properly called a theory.
• Bipolar flows from protostars were the first
  evidence of such disks.

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The Origin of the Solar System

• Modern techniques, though, can image the disks
  directly.

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Protoplanetary system HH30 with jets
400 AU
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The Origin of the Solar System

• The solar nebula theory supposes that planets
  form in the rotating disks of gas and dust around
  young stars.

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Protoplanetary Disks in Orion nebula HST
(Hubble Space Telescope)
100 AU