Proposed 900-telescope array could detect an Earth-like exoplanet's atmosphere in a single transit

What do you do when the observation you need comes around once a year? Well, preparation is key, but this is the awkward truth about finding another Earth. When a planet crosses the face of its star, a sliver of starlight passes through its atmosphere on the way to us, and the gases there absorb their own particular colors. Read the spectrum carefully and you can list what the air is made of: oxygen, ozone and water vapor, the things that would make you sit up.