Chapter 10, Part1: SunScorched Mercury

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Chapter 10, Part1 Sun-Scorched Mercury
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Earth-based optical observations of Mercury are
difficult.

• Mercury never gets far from the Sun.
• Mercury is briefly only visible right before
  sunrise (greatest western elongation) or just
  after sunset (greatest eastern elongation).

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Earth-based optical observations of Mercury are
difficult.
The tilt of Earths axis and the inclination of
Mercurys orbit combine to make favorable and
unfavorable observations.
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Earth-based optical observations of Mercury are
difficult.
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Mercury can be observed using radio telescopes
such as Arecibo.
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Mercury can be observed using radio telescopes
such as Arecibo, which bounce radio waves
revealing Mercurys rotation.
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Mercury rotates slowly and has an unusual 3-to-2
spin-orbiting coupling.
This tidal locking is exactly like the Earths
Moon (or Jupiters satellite Io), but has a 32
spin-obit coupling instead of 11
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Mercury rotates slowly and has an unusual 3-to-2
spin-orbiting coupling.
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Mercury rotates slowly and has an unusual 3-to-2
spin-orbiting coupling.
1 rotation completed
1.5 rotations completed
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Mercurys surface is inhospitable

• 88 days of daylight and 88 days of night.
• Daytime temperatures are 430ºC (800ºF)
• hot enough to melt lead
• Nighttime temperatures are -170ºC (-270ºF)
• Cold enough to freeze CO2 and CH4.
• Earth typically has temperature differences
  between day and night of about 11ºC (or 20F) .

On Mercury, the Sun moves from east to west,
except at perihelion where Mercurys movement
around the Sun outpaces its rotation and the Sun
appears to move backwards through the sky.
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Images from Mariner 10 reveal Mercurys heavily
cratered surface.
(Earths Moon on same scale at right for
comparison)
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Images from Mariner 10 reveal Mercurys heavily
cratered surface.
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Images from Mariner 10 reveal Mercurys heavily
cratered surface.
Mariner 10s three passes all resulted in the
same side of Mercury being photographed.
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Caloris Basin on Mercury
1300 km
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Edge of Caloris Basin 1300 km (810
mi) diameter
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The Focusing of Seismic Waves creates broken
hilly terrain opposite Caloris Basin
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Unusual, hilly terrain opposite the Caloris Basin.
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Radar Astronomy of Mercury1.
Determined rotation and 32 spin-obit coupling
(1964)2. Found evidence for ice in polar cap
craters (1999)
Arecibo (P.R.) Worlds largest radio telescope
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Possible ice deposits at Mercurys North Pole in
permanently shadowed craters.
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Like the Earth, Mercury has an iron core and a
magnetic field.

• Mercury is the most iron rich planet in the solar
  system.
• Mercurys core takes up 75 of the planets
  diameter.
• At least part of Mercurys core must be liquid
  for a magnetic field to be present.
• There must be a source of energy to make a liquid
  core flow to create a magnetic field.
• Mercurys magnetic field is a source of great
  mystery.

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Mercury likely had its outer layers (mantle)
stripped away by a catastrophic collision early
in its history leaving a planet made of mostly
iron.
The next mission to explore Mercury is the NASA
MESSENGER (MErcury Surface, Space ENvironment,
GEochemistry, and Ranging) Mission.
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Messenger Mission to Mercury

• Launch 2004, arrival 2009
• Science objectives
• Complete surface mapping (only 50 now)
• Is there water in polar cap craters?
• Why is Mercury so dense? Is it mostly Iron?
• Structure of magnetic field?
• Is there a outer liquid core?

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Guiding Questions

• What makes Mercury such a difficult planet to
  see? Too close to Sun greatest elongation only
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• What is unique about Mercurys rotation? Has 32
  orbital (88d) to rotational (58.6d) period ratio
  (due to tidal locking). This is called spin-orbit
  coupling
• How do the surface features on Mercury differ
  from those on the Moon? Very Similar (heavily
  cratered) but Mercurys plains are older,
  lighter in color.
• What evidence is there for ice on Mercury? Radar
  signals show high reflectivity in polar craters
  (Arecibo 1999)
• What is the Caloris basin? Huge 1300 km diameter
  crater, may have nearly split Mercury into
  pieces. Very old (4 Gyr)
• Is Mercurys internal structure more like that of
  the Earth or the Moon? More like Earths (large
  iron core)
• What spacecraft have visited Mercury? Future
  spacecraft? Only one (Mariner 10, 1974!)
  Messenger Mission will launch 2004, arrives 2009