I don't really understand how come no-one was able to see it before... I don't know how it works, but since telescopes are looking for stars and stuff much more distant that mars, I was confident that they scanned the whole surface of neighbors planets decades ago... Some explanation?
There's a limit for how big/small an object you can see with a telescope due to diffraction. For instance, the Hubble telescope can not distinguish features on the moon that are less than approximately 100 meters. Obviously it gets much worse for Mars and the other planets.
Mars (according to Wikipedia) has a surface area of 144,798,500km^2. This thing is within an area of 35 meters^2 and I'm guessing it's not very flashy when viewed on a screen.
