The key is the nature of the reflected light. Just in the last year an earth satellite was used to scan the reflection spectrum of earth to be used as a reference for the time when somewhat detailed reflection spectra start coming in from other planets. That time could be in about 8 years when NASA gets its planet-finder telescope launched into outer space.
They'll be looking for oceans, water clouds, continents, who knows, maybe even prairies and forests.
Thanks. Very informative. I had suspected that light refraction would play a key role in this, but I didn't realize that we could get such a wealth of detail. So, it appears that we'd be able to break down the composition of a planet's atmoshphere merely by studying how light refracts off it.
And you say we'll have planet-seeing telescopes in space... But will we get actual pictures, or computer constructs based on the data?