Astronomy 137 710 pm Tom Burbine tburbinemtholyoke.edu

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Astronomy 1377-10 pmTom Burbinetburbine_at_mtholy
oke.edu
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What are meteorites?
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Meteorite

• A small extraterrestrial body that reaches the
  Earth's surface

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Why are meteorites important?
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Why are meteorites important?

• They are primarily fragments of asteroids, which
  can hit us
• They are records of the early solar system

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Moon
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Meteorites

• Usually have ages of 4.6 billion years
• Asteroids and comets are thought to be the
  building blocks of the terrestrial planets

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Meteorites

• Many early cultures recognized (or believed)
  certain stones as having fallen from the sky
• Many early cultures had tools made from iron
  meteorites
• But to the scientists of the Renaissance and
  later periods, stones falling from the heavens
  were considered superstition or heresy

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More evidence

• In 1492, a meteorite weighing almost 130
  kilograms landed near the town of Ensisheim,
  Alsace, France, then in the hands of Germany

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Then ..

• In 1794, Ernst Friedrich Chladni, considered
  the father of meteoritics, published a book in
  which he concluded that stone and iron masses did
  fall out of the sky
• In 1803, thousands of meteorite fragments
  bombarded L'Aigle in Normandy, France, an event
  investigated by Jean-Baptiste Biot of the French
  Academy of Science.

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Thomas Jefferson

• Meteorite landed in Weston, CT
• It was brought to Yale where it was concluded it
  was from outer space
• Thomas Jefferson, President of the United states,
  was told about it

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And responded

• "Gentlemen, I would rather believe that two
  Yankee professors would lie than believe that
  stones fall from heaven."

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Meteorites

• Named after a nearby geographic locality

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Meteorite

• Esquel Pallasite
• Found in Esquel, Argentina

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Meteorites

• Almost all are thought to be fragments of
  asteroids
• Where else can they come from?

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Meteorites

• Almost all are thought to be fragments of
  asteroids
• Where else can they come from?
• Moon - 42 samples
• Mars - 34 samples
• Comets?
• Venus?
• Mercury?
• Other solar systems?

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Peekskill Meteorite
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• http//aquarid.physics.uwo.ca/pbrown/Videos/peeks
  kill.htm

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Meteorites

• Meteorites are composed of different minerals
• Silicates contain silicon and oxygen
• Sulfides contain sulfur
• Oxide contains oxygen
• Iron-nickel metal

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Meteorites

• Usually named after the town (or nearest town)
  where they fell or were located

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Falls and Finds

• Falls see them fall
• Finds find them

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Where is the best place to find meteorites on
Earth?
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Where is the best place to find meteorites on
Earth?

• Antarctica
• Deserts
• Sahara

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Basic Definition of Life

• Growth
• Metabolism
• Motion
• Reproduction
• Stimulus response
• http//en.wikipedia.org/wiki/LifeDefinitions

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Percival Lowell (1855-1916)

• Lowell produced intricate drawings of the Red
  Planet
• Finding hundreds of straight lines (termed
  "canals")

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He thought

• Lowell concluded that the bright areas were
  deserts and the dark were patches of vegetation
• Lowell thought the canals were constructed by
  intelligent beings who once flourished on Mars.

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For years

• People thought life could exist on Mars and
  Venus, the closest planets to Earth

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However,

• Venus is extremely hot (700-800 K)
• Atmospheric pressure is 90 times that of Earth

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Mars

• The average recorded temperature on Mars is
  -63 C with a maximum temperature of 20 C and a
  minimum of -140 C
• Atmospheric pressure is 1/100 of Earths

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In the past

• Mars appeared to be warmer and wetter

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Key to Life

• All life on Earth depends on water
• So if you find water, you may find life

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Habitable Zone

• The region around a star in which planets could
  potentially have surface temperatures which
  liquid water could exist

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Viking Missions

• Missions to Mars in 1976 to look for Life
• Two Missions to Mars to look for Life

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Experiments

• Three of the four experiments to look for life
  produced positive results
• But results could all be explained through
  non-biologic chemistry

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Earth

• Is the only planet known to have life

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SETI

• Search for Extra-Terrestrial Intelligence
• SETI programs tend to survey the sky to detect
  the existence of transmissions from a
  civilization on a faraway planet

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Intelligent Life

• You have to be able to build a radio telescope
• Of electromagnetic radiation, only radio and
  gamma can cross the Milky Way Galaxy
• It takes far less energy to produce radio waves
  than gamma rays

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Europa

• Moon of Jupiter
• Has an outer layer of ice

http//en.wikipedia.org/wiki/ImageEuropa-moon.jpg
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Europa

• Is thought to have a liquid ocean beneath an icy
  surface
• Energy source provided by tidal heating (keeps
  ocean from freezing)
• Proposed as possibly as possibly having
  extraterrestrial life

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http//www.planetaryexploration.net/jupiter/io/tid
al_heating.html
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www.physics.brandeis.edu/powerpoint/Charbonneau.pp
t
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The only star we know that has Earth-Like
Planets is the Sun

• Sun is sometimes called Sol

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Special Characteristics of the Sun

• It's a solitary star since most stars are
  binaries.
• Stable planetary orbits like the Earth's are much
  more likely around single stars.
• It is massive enough that it is not too cool or
  dim, but not so massive it that it burns out
  before life has time to develop, evolve, and
  manufacture an oxygen atmosphere to create an
  Earth-type planet.
• Appears to have roughly 50 percent more "heavy"
  elements than other stars of its age and type,
  but only about a third of their variation in
  brightness,
• elements heavier than hydrogen are essential to
  make rocky planets like Earth
• large stellar flare-ups can harm planetary life
  with hard radiation.
• http//www.solstation.com/habitable.htm

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Galactic Habitable Zone

• It is the area in the galaxy whose boundaries are
  set by its calm and safe environment, and access
  to the chemical materials necessary for building
  terrestrial planets similar to the Earth.
• http//astronomy.swin.edu.au/GHZ/

green is habitable zone
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Its place in the Galaxy

• One of Sol's unusual features is its orbit around
  the center of the galaxy, which is significantly
  less elliptical ("eccentric") than those of other
  stars similar in age and is barely inclined
  relative to the Galactic plane.
• This circularity in Sol's orbit prevents it from
  plunging into the inner Galaxy where
  life-threatening supernovae are more common.
• Moreover, the small inclination to the galactic
  plane avoids abrupt crossings of the plane that
  would stir up Sol's Oort Cloud and bombard the
  Earth with life-threatening comets.

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Habitable Zones

• http//en.wikipedia.org/wiki/ImageHabzonethinkque
  st.gif

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HabCat

• Catalog of Nearby Habitable Systems made by Jill
  Tarter and Margaret Turnbull
• These Sun-like, habitable stars have just the
  right distance, constancy, and temperature to
  qualify in a forthcoming enlarged radio search.

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What do else do you need?

• You need metals to make planets
• Metals are elements heavier in mass than helium

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For simple life

• You need a planet with an atmosphere and some
  water

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• Stars must remain nearly constant in brightness
  over billions of years for complex life to have
  time to develop.
• On Earth, single cells may have developed after
  only 800 million years or so, but the fossil
  record indicates that it took another 3 to 4
  billion years before multi-cellular life
  flourished.

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• The number of HabCat stars, as a function of
  distance
• M-type stars (solid red histogram)
• K stars (dark-hatched green histogram)
• G stars (light-hatched violet histogram)
• F stars (horizontal-lined yellow histogram)
• all stars (open blue histogram).
  http//www.astrobio.net/news/article436.html

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Drake Equation

• The Drake Equation is an attempt to estimate the
  number of extraterrestrial civilizations in our
  galaxy with which we might come in contact.
• http//www.activemind.com/Mysterious/Topics/SETI/d
  rake_equation.html

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Number of habitable planets

• 100 billion?

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Fraction of Planets that have life in the Galaxy

• ?

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Fraction of the Life-Bearing Planets in the
Galaxy upon which a Civilization capable of
interstellar communication has at some time
arisen

• ?

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Intelligent Life

• Intelligent life that we can detect is usually
  defined as life that can build a radio telescope

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Radio

• Transmitting information over radio waves is very
  cheap
• uses equipment that is easy to build
• has the information-carrying capacity necessary
  for the task
• The information also travels at the speed of
  light.

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Fraction of all civilizations that have existed
in the galaxy that exist now

• ?

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Fermis Paradox

• Where are they?

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Fermis Paradox

• Why have we not observed alien civilizations even
  though simple arguments would suggest that some
  of these civilizations ought to have spread
  throughout the galaxy by now?

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Reason for question

• Straightforward calculations show that a
  technological race capable of interstellar travel
  at (a modest) one tenth the speed of light ought
  to be able to colonize the entire Galaxy within a
  period of one to 10 million years.

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Explanation

• Interested in us but do not want us (yet) to be
  aware of their presence (sentinel hypothesis or
  zoo hypothesis)

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Explanation

• Not interested in us because they are by nature
  xenophobic or not curious

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Explanation

• Not interested in us because they are so much
  further ahead of us

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Explanation

• Prone to annihilation before they achieve a
  significant level of interstellar colonization,
  because     (a) they self-destruct     (b) are
  destroyed by external effects, such as
          (i) the collision of an asteroid or
  comet with their home world         (ii) a
  galaxy-wide sterilization phenomenon (e.g. a
  gamma-ray burster       (iii) cultural or
  technological stagnation

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Explanation

• Capable of only interplanetary or limited
  interstellar travel because of fundamental
  physical, biological, or economic restraints

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Fermis paradox

• The Fermi paradox is the apparent contradiction
  between high estimates of the probability of the
  existence of extraterrestrial civilizations and
  the lack of evidence for, or contact with, such
  civilizations.
• http//en.wikipedia.org/wiki/Fermi_paradox

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Any Questions?