A Radar Study of Mercury

1
A Radar Study of Mercury
2
Some Facts About Mercury

• Orbital period 88 Earth Days
• Distance from Sun 0.38 AU (58,000,000 km)
• Only 45 of its surface has ever been mapped (by
  Mariner 10 in 1974-5)
• Now Messenger is on its way (will arrive in 2011)
• Other studies done with radar imaging from Earth

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Mercurys History

• Named Hermes by the Greeks, the Romans changed
  the name to Mercury
• Schiaparelli studied Mercury from 1882-9 and
  stated that its day was the same length as its
  year! (88 Earth days)
• This was confirmed by 20th century observations
• But this is WRONG!

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Mercurys History, Ctd.

• Pettengill and Dyce (1965) used the Arecibo radio
  telescope to study Mercury using radar
• Mercury rotates once every 59 days! (Not once
  every 88)

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Using the Doppler Effect

• You can use the doppler effect to measure the
  rotation of a planet
• The side moving away from you is shifted red
• The side moving towards you is shifted blue

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Some Preliminary Calculations

• Radar waves dont come back exactly from the limb
• d ½ cDt
• c 3 x 108 m/s
• x R d
• y (R2 x2)1/2
• R 2.42 x 106 m is the radius of Mercury

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Data What It Looks Like

• You will get a two-shouldered profile when your
  signal returns
• Measure the frequencies of the left and right
  shoulders
• Be sure to note the T-value (thats Dt in your
  calculations)
• Remember that Dt is in microseconds (10-6 s)

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The Velocity of Mercurys Limb

• Dfc Dftotal/2
• ? Dftotal the difference in frequency between
  the two shoulders (right left)
• VA (cDfc)/2f
• f is the original radar frequency 430 x 106 Hz
• This is all so we can calculate the correct
  velocity of the planets limb
• V VA(R/y)

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The Rotational Period of Mercury

• Prot C/V
• C circumference of Mercury (C 2pR)
• Prot will be in seconds divide by 86,400 s/day
  to get it in days

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Basic Lab Procedure

• Open the Clea MERCURY lab on the computer
• Choose the coordinates for Mercury for today (I
  can show you how)
• Send your pulse and wait for it to return
• For each echo, note the time and measure the left
  and right shoulders