Radar probes of Mercury

Radar probes of Mercury

. A radio signal spreads out as a spherical wave, and only a small fraction is intercepted by Mercury. As the wave sweeps by the planet, it is reflected in spherical wavelets whose wavelengths are Doppler-shifted by the rotational motion of Mercury's surface. The waves from the receding side are red-shifted towards longer wavelengths and those from the approaching side are blue-shifted to shorter wavelengths. The total amount of wavelength change, from red to blue, reveals the speed of rotation, and the rotation period can be obtained by dividing the planet's circumference by this speed.

Copyright 2010, Professor Kenneth R. Lang, Tufts University