Transcript 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)
 Other studies done with radar
imaging from Earth

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!
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)
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
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
Data: What It Looks Like




You will get a “twoshouldered” profile
when your signal
returns
Measure the
frequencies of the left
and right shoulders
Be sure to note the Tvalue (that’s Dt in your
calculations)
Remember that Dt is in
microseconds
(10-6 s)
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)
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
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
