Phys 214' Planets and Life

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Phys 214. Planets and Life

• Dr. Cristina Buzea
• Department of Physics
• Room 259
• E-mail cristi_at_physics.queensu.ca
• (Please use PHYS214 in e-mail subject)
• Lecture 2. The possibility of life beyond Earth
• (Page 1-32)
• January 9

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Phys 214. Planets and life

• Textbook required
• Life in the Universe Second Edition 2007
• By Jeffrey Bennett Seth Shostak
• Other reading resources
• 1. Astrobiology A Multi-Disciplinary Approach
  (2004) by Jonathan Lunine
• 2. An Introduction to Astrobiology (2004)
• by Iain Gilmour, Mark A. Sephton
• 3. Planets and Life The Emerging Science of
  Astrobiology (2007)
• by Woodruff T. Sullivan John Baross

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Planets and Life

• Multidisciplinary study of the origin,
  distribution, and evolution of life
  (astrobiology).
• The disciplines
• Astrophysics
• Geology
• Planetary sciences
• Biology

Questionnaire to asses your interest levels for
various topics. During the next 34 lectures I
will try to accommodate your preferences allowing
more time for the highest ranked subjects.
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A Universe of Life

• Textbook pages 1-32
• The possibility of life beyond Earth
• How does astronomy, planetary sciences, and
  biology help us understand the possibilities for
  extraterrestrial life
• Places to search
• The ancient debate about life beyond Earth
• The Geocentric Model
• Explaining Retrograde Planetary Motion
• Ptolemaic Model
• Aristarchus (heliocentric) model
• Kepler - a Successful model of Planetary Motion
• Galileo proving the Earth is not the centre of
  everything
• Newtons three laws of motion
• The revolution in science

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The possibility of life beyond Earth

• The portrayal of most aliens in movies and on TV
  as being humanoid is probably unrealistic because
  the human form is most likely a result of the
  particular conditions and events that occurred on
  planet Earth.
• Extraterrestrial life could be similar to life on
  Earth or might be completely different.
• Extraterrestrial life is defined to be any kind
  of life beyond Earth
• Most important branches in the study of life in
  the Universe are Astronomy, Planetary science,
  Biology.

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Astronomy

• Astronomy shows that the Earth is just one planet
  orbiting an ordinary star in a vast universe.
• Astronomy shows that the fundamental laws of
  physics are the same everywhere in the universe.

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Planetary science

• Planetary science predicts that planets around
  other stars should be common.
• how planets are formed
• how planets work
• (why Venus is so much hotter than Earth, why the
  Moon is barren even if it is at the same distance
  from the Sun as Earth)
• what is a habitable world
• A habitable world is defined to be a world that
  has conditions suitable for life.
• The fact that the life on Earth seems to have
  appeared quite rapidly suggests that life can
  arise on most habitable worlds.

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Biology

• The laws of physics and chemistry are universal
• Could biology be also universal?
• The molecular building blocks of
• life have been found on the
• Earth, in interstellar clouds, meteorites.

Biology tells us that life on Earth can survive
over a wide range of environmental conditions.
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Places to search for life

• On Earth
• Our Solar System (8 planets, dwarf planets, gt150
  moons, asteroids, comets)
• looking for a liquid (water, methane)

Eris (Xena) 2005 - distance from the Sun is 96.7
AU, roughly three times that of Pluto. The
recently discovered Eris (Xena) is slightly
larger than Pluto.
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Places to search for life

• Among the planets, Mars is the most likely place
  to find evidence for life either now or in the
  past.
• If life exists on Mars today it will most likely
  be found beneath the surface.

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Places to search for life

• On the moons of Jovian planets.
• Europa might have all the conditions needed for
  both life to arise and life to survive.
• Ganymede and Callisto show some evidence of
  subsurface oceans, with less evidence for energy
  availability.
• Strongest evidence for the existence of a
  subsurface ocean of liquid water points out
  towards Jupiters moon Europa.

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Places to search for life
Titan

• Saturns moon Titan
• the only moon with substantial atmosphere
• too cold for surface liquid water (may have
  water underground)
• has liquid methane
• Evidence of subsurface liquids (including liquid
  water) on Saturns moon Enceladus and Neptunes
  moon Triton.

Triton
Enceladus
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Places to search for life

• Searching among the stars is more difficult -
  incredible distances to the stars.
• Pioneer 10 took 21 month to reach Jupiter (628
  million km from Earth).
• The closest star - Proxima Centauri is roughly
  4.2 light years from Earth, is 70,000 times
  farther away than Jupiter.
• A trip to the closest star would take more than
  100,000 years
• Searching for life with telescopes (extrasolar
  planets and their spectral signature).
• Earth-size planets detectable by 2010.
• Search for extraterrestrial intelligence SETI
  (civilizations might broadcast signals we could
  detect with radio telescopes).

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The new science of astrobiology

• The study of life in the universe is best
  described by the term astrobiology (NASA).
• Other names used exobiology, bioastronomy
• The goal of astrobiology is to
• 1) discover the connection between life and the
  places it is found
• 2) Look for such conditions on other planets and
  moons in our solar system and around other stars
• 3) Look for the actual occurrence of life
  elsewhere.
• According to modern views of our place in the
  universe, life elsewhere may be common.

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The ancient debate about life beyond Earth

• The possibility of extraterrestrial life was
  first considered many thousands of years ago
  during ancient times (at least 2300 years ago by
  the Greeks).
• For many thousands of years the Earth was
  believed to be a flat, motionless disk and the
  sky was a dome where heavenly objects moved.
• In order to understand the possibility of life
  beyond Earth, our ancestors had first to
  understand Earth as a planet, its place in the
  Solar system, and the Universe.
• Many civilizations made detailed astronomical
  observations
• - The Chinese kept astronomical observations
  beginning 5,000 years ago
• - Babylonians kept written records since 2,500
  years ago, predict eclipses.
• - Mayans observed the cyclical nature of time.
• However were not interested in constructing
  physical models explaining their observations.

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Early Greek Science

• The Greeks were the first to use methods we
  called today Modern Science.
• The basis of Modern Science
• 1) The Greeks tried to understand nature without
  resorting to supernatural explanations. The
  philosophers worked together, debating and
  testing each others ideas feature of the
  modern science of challenging every new idea.
• 2) Greeks developed mathematics in the form of
  geometry.
• Today, mathematics is a tool in exploring the
  implications of a new idea.
• 3) Greeks understood that an explanation about
  the world is correct if it agrees with the
  observed facts.
• Greeks used all three above ideas and created
  MODELS of nature.
• A scientific model is a conceptual representation
  for explaining and predicting phenomena.
• Even a failed model can be used in building a
  more accurate one.

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The Geocentric Model

• Anaximander (610-547 B.C.)
• The heavens form a complete sphere (celestial
  sphere) around Earth Geocentric Model.
• Greeks believed the Earth was round as early as
  500 B.C.
• Pythagoras (560-480 B.C.)
• Motivation for adopting a spherical Earth
  philosophical.
• Sphere is geometrically perfect.
• Aristotle cited observations of Earths curved
  shadow on the Moon during a lunar eclipse as
  evidence for a spherical Earth.

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Explaining Retrograde Planetary Motion

• While the patterns of constellations seem not
  change, the Sun, Moon, and the 5 planets visible
  with the naked eye (Mercury, Venus, Mars,
  Jupiter, and Saturn) gradually move among the
  stars.
• While the planets usually move eastwards compared
  to constellations, sometimes they reverse course
  and go westwards (backwards) apparent
  retrograde motion.
• This observation was very difficult to account by
  Greeks, who were ruled by the idea of heavenly
  perfection (Plato) all heavenly objects move in
  perfect circles.
• Composite of photographs of Mars between June and
  November 2003.

• The Sun and Moon move in ways easier to
  comprehend. Te planets (Mars, Jupiter) have much
  more complicated motions.

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Apparent Retrograde Motion
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Ptolemaic Model

• Claudius Ptolemy
• (100-170 A.D.?)
• Ptolemaic model explains retrograde motion by
  having all planets more around Earth in small
  circles that turned around larger circles.
• The model worked so well that remained valid for
  the next 1500 years.

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Aristarchus (heliocentric) model

• Aristarchus (310-230 B.C.)
• Aristarchus suggested that the Earth goes around
  the Sun, and not viceversa.
• The heliocentric model was rejected because it
  did not account for the Greeks experimental
  observations.
• If the Sun is the centre, Earth would be closer
  to different parts of the celestial sphere at
  different times of the year.
• This would create annual shifts in the position
  of the stars not experimentally observed by the
  Greeks.
• This meant that either Earth is at the centre of
  the Universe, or the stars are very far away.
• Stellar parallax apparent shift in position of
  nearby stars as the Earth moves around the Sun.

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Greeks argue about life beyond earth

• Thales (423-348 B.C.) the world consists of
  water, Earth floating on an infinite ocean.
• His student Anaximander, suggested a mystical
  element apeiron, meaning infinite. All
  materials come and return to apeiron, all world
  are born and die repeatedly. Through this idea he
  suggested that other Earths and other beings
  might exist at other times.
• Other Greeks stated that the world is build from
  four elements fire, water, earth, and air.
• Atomists argued that the heavens are made of
  an infinite number of indivisible atoms of the
  each of the four elements
• Aristotelians believed that the four elements
  were found on Earth while the heavens were made
  of a fifth element aether.

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Greeks ideas around the world

• Greeks ideas gained influence in the ancient
  world due to politics and war.
• Around 330 B.C., Alexander the Great expanded the
  Greek Empire through the Middle East and built
  the Library of Alexandria, destroyed in the fifth
  century.
• During Dark ages of Europe, building on the
  knowledge of the Greek manuscripts, scholars in
  the new intellectual centre in Baghdad developed
  mathematics, algebra, instruments and techniques
  for astronomical observations.
• When the Byzantine empire fell in 1453, many
  scholars headed west to Europe, leading to
  Europes Renaissance.

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Copernican Revolution

• Nicholas Copernicus (1473-1543)
• Copernicus revived Aristarchus idea of a
  Sun-centred solar system and described it
  mathematically, starting the Copernican
  Revolution.
• Copernican model did not become popular within
  the next 50 years, because it had many flaws,
  among which the perfect circular motion of
  heavenly bodies, forcing him to use incorrect
  assumptions (circles on circles motions, much
  like those of Ptolemy)

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Tychos observational data

• The lack of experimental quality data was
  necessary to improve either the Ptolemeic or
  Copernican model.
• During that time the telescope had not yet been
  invented, and the existing naked-eye observations
  were not accurate.
• Tycho Brahe (1546-1601) danish nobleman and
  eccentric genius built large naked-eye
  observatories.
• Over three decades Tycho made detailed
  measurements of the motions of the planets within
  a minute of 1 arc (1/60 of one degree).
• The discovery of a supernova by Tycho in 1572
  contradicted the commonly held belief that the
  universe was unchanging.
• Tycho couldnt explained the observed data, so he
  hired a German astronomer Johannes Kepler to
  explain it.

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Kepler- a Successful model of Planetary Motion

• Johannes Kepler (1571-1630) believed that
  planetary orbits should be circles, so he created
  a model able to explain Tycho observations. For
  planet Mars, Keplers predicted position differed
  from Tychos observations by 8 arcminutes (one
  fourth of the angular diameter of the full Moon).
• If I had believed that we could ignore these
  eight minutes, I would have patched up my
  hypothesis accordingly. But since it was not
  permissible to ignore, those eight minutes
  pointed the road to a complete reformation in
  astronomy.
• Kepler abandoned the idea of perfect circles and
  suggested planetary orbits as ellipses.
• He later developed Keplers laws of planetary
  motion.

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Keplers laws of planetary motion

• Keplers first law The orbit of each planet
  about the Sun is an ellipse with the Sun at one
  focus.
• The planet is closest to the Sun at perihelion,
  and farthest at aphelion.
• Planets average distance from the Sun is called
  semimajor axis.

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Keplers laws of planetary motion

• Keplers second law As a planet moves around its
  orbit, it sweeps out equal areas in equal times.
• The planet moves fastest in its orbit when it is
  at perihelion.

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Keplers laws of planetary motion

• Keplers third law More distant planets orbit
  the Sun at slower average speeds, obeying the
  precise mathematical relationship
• where p is the planets orbital period in years,
  and a is the average distance (semimajor axis)
  from the Sun in astronomical units (AU).

1 AU Earths average distance from the Sun
149.6 million km Kepler published his laws
between 1610-1618. His model predicted
accurately planetary motion.
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Galileo answering remaining objections

• Galileo Galilei (1564-1642)
• Galileo Galilei built a telescope and obtained
  the first observational evidence suggesting the
  Earth moved about the Sun.
• He showed imperfections in heavens spots on the
  Sun, mountains on the Moon, contradicting the
  common belief that the Heavens were perfect.
• He showed imperfections in heavens spots on the
  Sun, mountains on the Moon, contradicting the
  common belief that the Heavens were perfect.
  Galileo observed 4 moons orbiting Jupiter, not
  Earth.
• Galileo observed 4 moons orbiting Jupiter, not
  Earth.

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Galileo proving the Earth is not the centre of
everything

• Galileo observed Venus goes through phases in a
  way that proved its orbits the Sun and not the
  Earth.
• With the proof from Galileo, Keplers model of
  planetary motion was unanimously accepted by
  1630, however no one understood why planets moved
  in elliptical orbits with varying speeds, until
  Sir Isaac Newton.

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Newtons three laws of motion

• Sir Isaac Newton (1642-1727) invented calculus
  and used it to explain many fundamental
  principles of physics. He also proved Keplers
  laws are natural consequences of the laws of
  motion and gravity.
• Newtons laws are general and apply to any
  motion, while Keplers laws apply only to
  planetary motion in the solar system.

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The revolution in science

• The scientific revolution started by Copernicus
  in 1543 and continued by Kepler and Newton caused
  a radical change in human perspective on our
  place in the universe.
• Earth is not regarded anymore as the centre of
  the universe, but just one of the many words.
• The science was not led by aesthetics anymore,
  perfect circles, indivisible atoms, and guessing
  was no longer good enough.
• Experimental evidence backed up by rigorous
  mathematics was required for a model to be
  accepted.

Newton
Copernicus
Kepler
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The ancient debate about extraterrestrial life?

• Democritus (470-380 B.C.) argued that both Earth
  and Heaven were created by random motion of
  infinite atoms. Because of the infinite number of
  atoms, one can assume other worlds similar to
  ours exist.
• A later atomist, Epicur (341-270 B.C.) writes
• There are infinite worlds both like and unlike
  this world of ours we must believe that in all
  worlds there are living creatures and plants and
  other things we see in this world.
• Aristotle differed in his opinions, rejecting the
  atomist idea of different worlds. Each of the
  four elements had its own motion and place (Earth
  moves towards the centre, fire moves away from
  the centre. It there was more than one world it
  should be more than one natural place for the
  elements to go, being a logical contradiction.
  The world must be unique There cannot be
  several worlds.

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The ancient debate about extraterrestrial life?

• Galileo suggested than the lunar features he saw
  with his telescope might be land and water, much
  like on Earth.
• Kepler went further, suggesting the Moon had an
  atmosphere and was inhabited by intelligent
  beings. He even wrote a science fiction story,
  Somnium (The dream) describing lunar
  inhabitants.
• Giordano Bruno (1548-1600) was convinced in the
  existence of extraterrestrial life. In his book
  On the Infinite Universe and Worlds he wrote
• It is impossible that a rational being can
  imagine that these innumerable worlds, manifest
  as like to our own or yet more magnificent,
  should be destitute of similar or even superior
  inhabitants.

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The ancient debate about extraterrestrial life?

• William Herschel (1738-1822) and sister Caroline,
  co-discoverer of planet Uranus, assumed that all
  planets were inhabited.
• Percival Lowell (1855-1916), a rich Harvard
  graduate documented canals on Mars from his
  observatory, believing they are constructed by
  Martian civilization.

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Next Lecture

• Movie Lecture 3. Exercise on Keplers laws
  (Page 28-30)
• Part III Carl Sagans Cosmos - Keplers laws -
  The harmony of the world.
• Episode 8 (35 min)