File:KSC-05-S-00263 (ksc 080805 mro smrekar14).webm

English: Elias from Sao Paulo: Can you explain how the sounder that is among the instruments of the MRO works? Also, how can it find or look for subsurface waters in Mars? Okay. Well, probably most people have seen like an ultrasound image. When mothers are pregnant, often these days ultrasounds are done. And it's the same kind of concept. You have waves that travel inside a solid body, but there are different places where the properties change. So when you look at a picture of a baby, what you see mainly are the bones. You see like the skeleton, and it looks kind of odd, but those are the most dense parts, of the, of the tissues and bones. I'm sorry, tissues and liquid and everything else that's in there, but what you see, what really stands out are the bones. And with radar, it's not the density that matters, it's their electrical properties that matter. So the radar detects different layers, when the electrical properties of those layers change, or when there's a big gap between one layer and the other, there's kind of a break in those properties. So, if you have one layer sitting over another, if it has somewhat different properties, you'll see that interface and the radar waves will be reflected back off that interface. Now it turns out, you know, we know water is a very good conductor, and water has a very big difference in its electrical properties from rock. So if there's a big lens of water in the subsurface, you'll get a really, really strong reflection off that water in the subsurface. So that's how it can detect layers, by seeing these changes in the electrical properties.