 Casis is a high-resolution color stereo camera in Mars orbit and is making remarkable images of the red planet. So what mysteries has it revealed today? Recently Casis observed some dark tracks on the Mars surface. Looks a little like giant worm tracks but for the moment we still haven't found life on Mars so it can't be that. So what has produced these tracks? These tracks are seen over many parts of Mars and especially where there's a lot of dust. Well you heard right there's a lot of dust on Mars and dust is a key to the puzzle of the red Martian sky. The Earth's sky is blue but dust in the atmosphere strongly influences the color and brightness distribution of the sky. So if you stand on the Martian surface and turn around you would see that the sky is actually red and varying in brightness much more strongly than on Earth and surprisingly near the Sun the sky will be blue. Hmm if there's dust in the atmosphere it should have been brought there by winds right? You've seen the Hollywood movie The Martian? Well you can imagine that maybe some stones were moved by these winds and left the tracks but let me surprise you here. The Martian atmospheric density is only about 1% of the Earth's atmospheric density so even a high-speed wind can't move anything except dust. To search for the answer let's go to the most dusty places on the earth. Let's look at this. Looks similar doesn't it? You might think that somebody decided to clean the ancient dust on the planet's surface but look at the scale of these casis images. The tracks can be several tens of meters in width. That's a very very big finger. But what if we combine dust and wind? Let's look for evidence in a dry desert region on Earth. Here the Sun warms up the air near a flat dry surface. The warm air rises quickly and begins spinning moving forward as more air is sucked in below. This spinning moving cell picks up dust and sand and leaves behind a clean surface. If we're right, casis should detect some of these revolving structures. And here we are. We seem to have captured our devil. To understand more let's implement the power of casis. The stereo capability of casis allows observation from two different directions separated in time by just 45 seconds. So we combine two stereo pictures together and... got it! This is a dust devil and it's moved a lot in 45 seconds. We can even calculate its speed as we know the distance. And hey presto! 8 meters per second. That's a little slower than the speed of the fastest Olympic champion Usain Bolt when he's running a hundred meters. And here is one more. Look at the shadow. It is huge! Just imagine that. Dust devils on Mars can reach 700 meters in diameter and several kilometers in height. It's extraordinary. It's several tens of times more than on Earth. Why is that? Well there are two keys here. One is the lower Martian gravity and the other is the rarefied atmosphere. Although Mars is definitely a different world, sometimes casis can show us things that are very familiar to us on Earth. Got it! What on Earth are you doing here worm? Look at that! I wonder what's making that change in brightness?