Re: Could someone use the electromagnetic fields of the planets and sun?

Hi Chris!

An antenna has to be carefully tuned in order for it to resonate with a 
transmitted signal. This resonance manifests itself as a very small 
varying voltage across the antenna, and has to be carefully amplified to 
enormous levels - many millions of times and more - to keep random noise 
as low as possible, and to enable the signal to be of any practical use.

Whilst it is certainly possible to alter another planet's electromagnetic 
field (the Sun has an effect on the Earth's field, and Jupiter has an 
effect on Io's field, for example) it would be impossible at current radio 
power levels to alter a distant body's electromagnetic field to any useful 
degree. Additionally, there would be no distant "on-site" control and 
amplification of the received signal at the body, thus ruling it out as a 
method of repeating and thereby increasing the range of sensors.

That said, astronomy almost solely relies upon the passive detection of 
electromagnetic fields of distant bodies in order to study them: whether 
visible light, radio waves, x-rays, etc. Only in a few cases are active 
sensors employed: these include radar and lidar (radio waves and light 
waves, respectively) to directly probe the distances to, and surfaces 
features of, distant bodies.

Andy Goddard