Most of the methods proposed for detecting life on other planets are based on biochemical signatures, starting with the life detection experiments on the Viking Mars landers of the 1970s. Now a group of researchers from Switzerland and Belgium have proposed—and tested—a very different approach, which they discuss in a recent article in Proceedings of the National Academy of Sciences.
Sandor Kasas of the École Polytechnique Fédérale de Lausanne and his colleagues used a nanomotion detector to determine tiny fluctuations associated with the movement and metabolic activity of cells. What makes this technique new and exciting is that it’s independent of biochemistry, and thus does not require prior knowledge of the metabolic pathways used by alien organisms, which are challenging to determine in extraterrestrial environments.
The team’s mechanical nanosensor uses a very small cantilever—essentially a beam anchored at one end—to detect extremely small motions. The other end of the beam takes the load, which in this case are cells. The cantilever scans any surface—for example, the face of a mineral—like the needle of an old vinyl record player, and its up-and-down movement is read by a laser to produce an image. Any cell on the other end of the cantilever is likely to show some metabolic movement, perhaps even physical movement, which would be recorded.
Kasas and his colleagues tested their nanoscale detector with bacteria and yeast, as well as mouse cells, human cells, and plant cells. It worked each time, and the signal was easily discernible from the background signal, which was determined after the cells were killed by a toxic compound. Even more remarkably, the detector worked well with a soil and a water sample that contained microorganisms. The signal was again easily discernible from the background after these samples were sterilized.
This new method has important advantages for astrobiology. It’s based on a relatively simple mechanism, and a positive identification can be obtained in just 10 minutes. The nanoscale detector could easily become a key tool for searching for life on other planets based on the small size of the detector, the short testing time, and the fact that no prior information about the biochemistry of any putative organism is required. This would be especially helpful when paired with more traditional biochemically-based life detection methods in places such as Saturn’s moon Titan.
As always, further testing is required, along with experiments to determine the lower cell detection limit and figure out the best way to get organisms to the cantilever in an alien environment. But if the nanoscale detector turns out to be as useful as it looks, it could also help us determine which extreme environments on Earth are inhabited and which are not, thus providing further insights on the limits of life on our home planet.