That (hat tip: universe today) is what Venus Express is doing to Earth. As the name suggests, it is orbiting on the planet Venus, that really cloudy, hot planet. What use can looking at a smallish blue dot be, you ask? Well, if you take the light coming from an object, and separate its colors, through the bands of colorst that is reflected, you can see the composition of heavenly objects, like stars and planets. This will be potentially useful when looking for life in another planet. If one knows the signature color bands for planets with life, one can apply this to other exoplanets. That is what Venus Express is doing. By taking the spectrum of the Earth, they are trying to look for the chemical compostitions of Earth that gives a sigunature that life exists.
Looking Back at Earth