By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET

What comes out of the human body and goes into a toilet is often thought of as an end product. But for future residents of Mars, human waste will need to take on a more vital role.

Like becoming fertilizer for growing food.

Because it costs thousands of dollars to lift every pound of stuff into space, and even more to get it to Mars, mission planners don’t want to waste a thing. Human excrement, being rich in nutrients, can be a composter’s dream. So a group of European researchers is taking on the task of figuring out just how to safely manage a high-tech Martian outhouse.

Because somebody, of course, has to do it.

The European Space Agency is building an “artificial ecosystem” near Barcelona, Spain, that will use three rats to test an idea for processing rodent waste with microorganisms. The rats will be kept under close veterinary supervision throughout the test, according to ESA officials.

Rats, it seems, have more in common with humans than you might have realized. Their oxygen demand and carbon dioxide production are roughly equivalent to ours, for example. Certain microorganisms, on the other hand, have a penchant for dealing with whatever comes their way.