Mercury

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Mercury
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Bulk Properties

• Radius 0.38 Earth radii
• Mass 0.055 Earth masses
• Mean density 5.4 g/cm3
• Semi-Major Axis 0.39 AU (0.31-0.47)
• Very Eccentric
• Orbital Period 88.0 days
• Rotational Period 58.7 days
• Motions combine to make each day 2 years long
• 3 months of sunshine / 3 months of darkness

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Why no synchronous orbit?

• Because of Mercurys proximity to the Sun and the
  Suns mass, we would expect Mercury to be
  tidally locked in its orbit
• Mercurys eccentric orbit prevents it from
  becoming synchronous
• Orbits faster at perihelion, but rotates at a
  constant rate

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Mercurys Surface

• Temperature
• Daytime 700 Kelvin
• Nighttime 100 Kelvin
• Largest range in the solar system
• Gravity
• 0.4x Earths gravity
• 2.5x Moons gravity

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Surface Features

• Heavily cratered, though not as much as the Moon
• Crater walls not as high as the moon (higher
  gravity)
• No maria, though past volcanism is suspected
• Scarps
• Large cracks in the crust
• Probably formed when the planets core cooled and
  shrank

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Prominent Features

• Caloris Basin
• Large impact crater
• Concentric rings
• Opposite side of Mercury wrinkled from the
  impact
• weird terrain
• Intercrater Plains

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Mercurys Interior and Magnetosphere

• Very large iron-rich core
• About 40 of Mercurys volume
• Lunar-like mantle and thick crust
• Magnetic Field is about 1/100 that of Earth
• Could be the result of a currently rotating
  partially molten core (dynamo)
• Could also be a remnant of a formerly molten core

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Mercury Exploration

• Mercury can only be observed telescopically near
  sunrise or sunset
• Mercury never appears further than 28 degrees
  from the Sun
• It is the least explored inner planet because its
  proximity to the Sun makes it difficult to send
  probes

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Mariner 10

• Launched in November 1973
• Placed in orbit around the Sun
• Exactly twice the orbital period of Mercury
• Three fly-bys in 1974 and 1975
• Same side of Mercury was lit each time
• Only 45 of the surface was photographed
• Detected the magnetic field
• Ran out of fuel in 1975

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MESSENGER

• MErcury Surface, Space ENvironment, Geochemistry,
  and Ranging
• Launched August 2004
• Will enter Mercury orbit in 2011
• Completed fly-by in January 2008 and October 2008
• One more fly-by in September 2009

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