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Radar Study of Mercury: Rotational Period and Historical Discoveries

Explore Mercury's unique characteristics through radar imaging, including its orbital period, surface mapping progress, and rotational period. Learn about historical observations and how radar technology has unveiled new insights into this mysterious planet.

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Radar Study of Mercury: Rotational Period and Historical Discoveries

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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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