In 2020, a spacecraft lands on Europa and melts its way through the ice into the Europan ocean' It f

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In 2020, a spacecraft lands on Europa and melts
its way through the ice into the Europan ocean.
It finds numerous strange, living microbes, along
with a few larger organisms that feed on the
microbes.

• This is fantasy because the X-ray emission from
  Saturn has effectively sterilized all the moons
  around it.
• This is fantasy because it would take more than
  20 years for a spacecraft to reach Saturn with
  current technology.
• This is possible because there is evidence for an
  ocean underneath the icy surface of Europa and
  water is a good place to look for life.
• This is likely because molecules produced only by
  life were already detected on Europa by Voyager 2.

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18.2 Life in the Solar System

• Our goals for learning
• Could there be life on Mars?
• Could there be life on Europa or other jovian
  moons?

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Could there be life on Mars?

• Mars had liquid water in the distant past
• Still has lots of subsurface ice possibly
  subsurface water near sources of volcanic heat.

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In 2004, NASA Spirit and Opportunity Rovers sent
home new mineral evidence of past liquid water on
Mars.
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Close-up view of round pebble apparently formed
in water on Mars.
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The Martian Meteorite debate
composition indicates origin on Mars.
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• Does the meteorite contain fossil evidence of
  life on Mars? (left Mars right Earth)

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Could there be life on Europa or other jovian
moons?
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• Ganymede, Callisto also show some evidence for
  subsurface oceans.
• Relatively little energy available for life
• Nonetheless, intriguing prospect of THREE
  potential homes for life around Jupiter alone.

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Titan

• Surface too cold for liquid water (but deep
  underground?)
• Liquid ethane/methane in places on the surface
• ...but not at Huygens probe landing site, Jan.
  2005
• No evidence for surface life (if any, probably
  quite alien)

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What have we learned?

• Could there be life on Mars?
• Mars once had conditions that may have been
  conducive to an origin of life. If life arose, it
  might still survive in pockets of liquid water
  underground.

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What have we learned?

• Could there be life on Europa or other moons of
  Jupiter or Saturn?
• Europa probably has a subsurface ocean of liquid
  water, and may have undersea volcanoes on its
  ocean floor. If so, it has conditions much like
  those in which life on Earth probably arose,
  making it a good candidate for life beyond Earth.
  Ganymede and Callisto might have oceans as well.
  Titan may have other liquids on its surface,
  though it is too cold for liquid water. Perhaps
  life can survive in these other liquids, or
  perhaps Titan has liquid water deep underground.
  Enceladus may have subsurface water, or it may
  just have slush.

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What suggests there could be life on Mars?

• A) Evidence of liquid water at or near the
  surface, and evidence there was more water in the
  past
• B) Mars has the closest climate to Earths in the
  solar system. It is colder than Earth but was
  warmer in the past
• C) Mars has an atmosphere
• D) All of the above
• E) A and C

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Should we send humans to Mars and search for life?

• Yes, if we found evidence of life it would have
  important scientific implications
• Yes, if we found evidence of life it would have
  major scientific, philosophical, and religious
  implications
• No, its too expensive
• No, at best were likely to find fossils, and
  they arent interesting enough
• Of course there is or was life on Mars. We dont
  have to actually go there to find out

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Activity 21, pages 75-78

• Well do questions 1-3 and 7-8

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1. Which of the following is true for the moving
point source in Figure 1?

• Wavelength shortest to left and longest to right
  star moving to right
• Wavelength shortest to left and longest to right
  star moving to left
• Wavelength shortest to right and longest to left
  star moving to left
• Wavelength shortest to right and longest to left
  star moving to right

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2A. For the observer in Figure 2, which two
velocity arrows will NOT produce a Doppler shift?

• A and B
• A and C
• C and D
• A and D
• C and E
• D and E
• None of the above

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2B. For which velocity arrows in Fig. 2 can the
astronomer measure the total velocity, and for
which only a component of the velocity?

• Total for A and D, component for B, E and C
• Total for B, E and C, component for A and D
• Total for C and E component for A, B and D
• Total for A, B and D component for C and E

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3. The star in Figure 3 has a

• Blueshifted spectrum, so its moving away from us
• Blueshifted spectrum, so its moving towards us
• Redshifted spectrum, so its moving away from us
• Redshifted spectrum, so its moving towards us

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7. In Figure 4, which of the following is true
for the smaller star moving in its circular orbit?

• Redshift at A, blueshift at C, no shift at B and
  D
• Redshift at B, blueshift at D, no shift at A and
  C
• Redshift at C, blueshift at A, no shift at B and
  D
• Redshift at D, blueshift at B, no shift at A and C

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8. In Figure 5, when the radial velocity of the
smaller star is plotted versus time,

• Velocity is zero at B and D, positive (farthest
  above the line) at A, negative (farthest below
  the line) at C
• Velocity is zero at A and C, positive (farthest
  above the line) at D, negative (farthest below
  the line) at B
• Velocity is zero at B and D, positive (farthest
  above the line) at C, negative (farthest below
  the line) at A