Mercury

1
Mercurys Molten Corehow do we knowand what
does it mean?Lindsay JohannessenPTYS 395

• All images courtesy of NASA/JPL and Science
  Magazine

2
The Basic Facts

• Mercurys
• Mass 0.055
  (Earth1)
• Density 5.43 (g/cm3)
• Gravity 0.284
  (Earth1)
• Orbit Period 87.97 (Earth days)
• Rotation Period 58.65 (Earth days)
• Eccentricity of Orbit 0.206
• Was previously thought to have solidified, cooled
  iron core
• New evidence states otherwise. Mercurys core is
  partially molten!

3

• Astronomers already knew
• Mercury had a pre-existing magnetic field.
• A dynamo-like construction would be needed to
  form/sustain said magnetic field.
• With a dynamo construction in Mercury, the core
  would not be composed of just Iron, but at least
  a certain percentage of lighter elements .
• What Astronomers Didnt Know
• at first was how to accomplish these goals
  without waiting for MESSENGER to land.
• the accuracy of two calculations the tilt of
  the spin axis and gravitational field at the
  poles and equatorial regions.

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What did they do?

• Using radar echoing from NASA/JPLs DSS-14
  antenna at Goldstone, CA, the Green Bank
  Telescope (GBT) in WV, and the Arecibo Telescope
  in Puerto Rico
• Data was taken at each location.
• With signals being sent out,
• there were two telescopes recording
• data from each respective signal.
• With the speckle patterns in the
• data being recorded and analyzed, the astronomers
  were able to
• detect oscillations, or forced librations in
  the rotation of Mercury.

5

• What does Mercurys spin rate have to do with
  anything?
• By calculating the slight variation in the
  rotation period of Mercury, astronomers are able
  to compare the results of their radar echoing to
  those of theorized spin rates of solid bodies.
• These comparisons are of huge significance. After
  obtaining these variations in Mercurys rotation,
  astronomers found a distinct pattern in
  oscillations they call forced or longitudinal
  librations.

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• These librations, when compared to those of a
  solid body, are of much greater amplitude than
  they should be.
• This data observation gives evidence of a molten
  core. The inner core and the crust of the planet
  must be decoupled, or somehow loosely connected
  via a fluid substance in order for this amplitude
  of oscillation to occur.
• - Notice the eccentricity of the
  orbit. How does this uneven gravitational
  pull effect the rotation libration when
  the body is not completely solid?

7

• Compare with boiled egg testand add a
  gravitational force.
• Take into account that
• scientists now have
• evidence to support
• the dynamo theory
• for Mercury. This
• helps explain the
• magnetic field which is
• now theorized to be
• continuous, not residual.

8
Problems. Dundundun

• Is it actually possible for this tiny planet to
  still have a hot core?
• - Not as far as modern science has theorized.
• So if the core isnt hot enough, can it still
  somehow be molten?
• - If sulfur is present, YES.
• Can sulfur be there in the core of the planet
  closest to our sun?
• - All experimentation and theory point to NO.
• During the formation of the solar system, the
  heavier elements gravitated towards the
• sun to form the terrestrial planets. Sulfur, not
  being one of those, would need to have
• an occupancy of 0.1 weight fraction in Mercurys
  core to keep the outside mantle
• from freezing. This, as small as it seems, is
  still too far from theory.

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• What answers are we hoping MESSENGER will bring?
• - MESSENGER will acquire mineralogical and
  compositional data to help discover why Mercury
  is as dense as it is.
• - MESSENGER will closely study Mercurys
  gravitational field to confirm the outer core is
  molten.
• - MESSENGER will study Mercurys exosphere to
  determine its characteristics more in-depth and
  the processes by which it came about.