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A Radar Study of Mercury

A Radar Study of Mercury. 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)

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A Radar Study of Mercury

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  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

  3. Mercury’s 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!

  4. Mercury’s 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)

  5. 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

  6. Some Preliminary Calculations • Radar waves don’t 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

  7. 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 (that’s Dt in your calculations) • Remember that Dt is in microseconds (10-6 s)

  8. The Velocity of Mercury’s 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 planet’s limb: V = VA(R/y)

  9. 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

  10. 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

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