Just a little something to think about...

If I have a wire, radius r, nominally infinitely long, in free-space,
does it have non-zero capacitance per unit length?

A sphere in freespace has capacitance directly proportional to its
radius: C = 4*pi*epsion.zero*radius. So the earth, in something
approximating freespace, has a bit over 40uF of capacitance. But what
about a wire?

A coaxial capacitor (the capacitance between conductors of a coaxial
cable, for example) with vacuum (or essentially with air) dielectric
and inner conductor radius a and outer conductor inner radius b, has
capacitance C per unit length L given by

C/L = 2*pi*epsion.zero/(ln(b/a))

As b goes to infinity (the wire in freespace case), C/L goes to zero.

So if I have a thin wire, 15 meters long, out in freespace, and a 10MHz
(30 meter wavelength) EM wave comes along and passes by that wire, what
happens in the wire?

Cheers,
Tom