When an organism dies, it leaves behind a lot more than just flesh and bones. It leaves behind a trail: traces of its movements, perhaps footprints, and waste... lots and lots of waste. In fact, the amount of direct evidence (a body) that any organism leaves behind pales in comparison to the amount of indirect evidence (waste) that it generates during its life.

It therefore makes a lot of sense that if we're going to look for signs of alien life on other planets, that we'll improve our odds if we expand that search for the trail those organisms might have left behind. In other words, perhaps we should be looking for alien poop, reports New Scienist.

That's the idea behind a new research effort led by Andrea Baucon at the University of Modena, Italy. Baucon and his team have suggested that astrobiologists should do more than just search for living and fossilised creatures; they should look for their trail, whether that be alien footprints or their excrement.

“You have a heck of a lot more chance of finding the trace of an organism than you do the actual organism itself,” explained Lisa Buckley, a paleontologist at Peace Region Palaeontology Research Centre in British Columbia, Canada. “One animal will leave countless traces in its lifetime, but it’s only ever going to leave one body fossil.”

For instance, it's possible that Mars-- though seemingly barren today-- once hosted life. Fossils are difficult to search for, but if there's evidence that the landscape has been disturbed in some way, in a way that can't be explained by geology or the weather, it could point the way to where the aliens, living or dead, might be hiding. It's also worth considering that life on another planet might never have evolved skeletons or hard exteriors, making fossils difficult to come by. Maybe the aliens were (are?) soft-bodied.

It's worth considering. No matter what a creature is made out of, it must still consume energy and dispose of waste. So it's important for astrobiologists to be able to tell the difference between waste made my living creatures, and formations generated by natural phenomenon. At the very least, it's a chapter in the astrobiologists' handbook that has yet to be written.

Wouldn't that be something, to discover alien scat petrified on the surface of Mars or Titan? And would we recognize it if we saw it?