according to my sensors, Captain...

Even as a kid, I found it a bit of a stretch. While watching Star Trek (the original series), the Enterprise would wander into some uncharted solar system, and with their ship sensors, monitored by a Vulcan half-breed peering into a shielded display (what was that about?), would pick off the habitable planet and describe its atmospheric composition. Presumably, from 50 or 100 AU away. Crazy.

Now, today, not-science-fiction, we're picking up atmospheres of planets dozens of light years away! Crazy.

Previous observations of HD 189733b by Hubble and the Spitzer Space Telescope found water vapour. Earlier this year, Hubble found methane in the planet's atmosphere.

http://www.nasa.gov/mission_pages/hubble/news/CO2.html

Mark Swain, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., used Hubble's near infrared camera and multi-object spectrometer to study infrared light emitted from the planet, which lies 63 light-years away. Now they are identifying carbon dioxide.

And that really got my brain going...

Maybe, in the not too distant future, stuck on Earth, still unable to travel near, at, or above light speed, we'll be able to spot planets with a thin layers of nitrogen, oxygen, some argon, and a bit of CO₂.