they're right on the very edge of that operating capability. if they move to the north, it drops rapidly to about 6,000 meters. if they go a bit to the south it climbs up to 2,000 meters. but i think it is to the north that it could cause a problem. >> what happens if it goes deeper? >> it would float -- -- it would implode. >> gets crushed because of the pressure? >> yeah, and i know they're thinking about that. they can fly higher above the terrain. >> it is called a side scanning sonar, but does it have a depth of -- i mean, can it scan at a certain depth? does it have to be on the same level or can it scan what's below? >> it's range versus resolution. if you want to see further, you can come up off the bottom. just like in an airplane, the high er you are, the further yo can see. you have less of an idea of what you're looking at. if you want an accurate view -- >> are there rovers that can do that?