I’ve seen articles about underground water being detected in planets like Mars. I’m assuming it’s detected via satellite (microwaves?), but how does the technology work?
And are we using the satellite that’s orbiting around earth and projecting the (microwaves?) there, or do we send a few satellites specifically to Mars to do these investigations?
In: Technology
There’s a variety of methods, but the most common one is surface penetrating radar.
When you deal with long wavelengths of light in the radio range, the ground actually becomes somewhat transparent. If you think about glass, most of the light goes through but a small amount gets reflected back at you. Whenever light reaches an interface of materials, some light gets reflected back, and how much gets reflected back depends on what the material is made of (specifically the dielectric constant of the material when dealing with radar). By sending a pulse down, you’ll get a small reflection off the surface, but most of the light will continue into the ground. If there is a change in material under the surface, you’ll get another reflection and the properties of the reflection can tell you what the material change was. However, do note that this could be a liquid water aquifer, a solid mass of ice, a region of higher water content in the regular rock, or a totally unrelated mineral formation that just happens to reflect like water does. Usually, when you hear big breakthroughs about water on Mars, it’s actually that last option that gets misinterpreted.
There is at least one Mars orbiter with a surface penetrating radar (SHARAD on MRO).
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