Blue sky on Mars.
<"Tell me again why a blue sky on Mars is impossible?"
Not impossible if you have an Earth-like atmopheric condition. The problem is that dust-light interaction is the dominant process on Mars unlike the Earth where it's Molecular, but it can be dust or particulate dominated on the horizon if you live in a large city. Especially in Texas.....
A good explanation can be found here.....
http://humbabe.arc.nasa.gov/mgcm/faq/sky.html
Some technical info can be found here
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html