Hi SM and the guys

Well GRBs certainly put out a lot of energy, but not a lot would be reflected - most is absorbed by whatever the gamma-rays hit. And not a lot of gamma-rays, in terms of numbers, are received for the same amount of energy as radio waves.

The nuclear explosion scenario was first proposed by Arthur Clarke [I think] in the first Rama sequel. And a nuke would put out a lot of radio waves in one big pulse that would "light up", in radio, virtually everything radar reflective in Sol Space.

GRBs however are a LOT further away. Sol space is about 100 AU wide. One light year is 63,240 AU and GRBs are BILLIONS of light years away... diminishing the return signal by a factor of 10^25 [10 trillion trillion] squared - i.e. 10^50. Isotropic Radar pulse reflection varies according to an 1/x^4 law.

A GRB only pumps out about 10^44 Joules and the radar reflections of exosolar planets would be impossible to resolve at light year distances. But the main problem is absorption - virtually nothing will reflect gamma rays.

We're better off building space-based interferometers to image exoplanets directly.

Adam