Most people are familiar with the pale blue dot image of Earth taken by Voyager in 1990. Its blueness is significant, of course, because it is Earth’s abundant liquid water that makes it look that way.
But if you looked at the light that is reflected from Earth carefully, you would see several interesting features. One, caused by vegetation, is called “red edge”. Green plants absorbs a lot of red light creating a big, sudden jump in reflectivity in the red bit of the visible light spectrum. An alien, if it could get a good look, would be able to tell than Earth had plenty of vegetation because of this red edge.
A paper recently uploaded to arXiv (accepted for publication in the journal Astrobiology) looks at what features, like vegetation, we might be able to discern on a planet outside of our solar system.
To read more, click here.