When the crewmembers of the starship Enterprise pull into orbit around a new planet, one of the first things they do is scan for life-forms. Here in the real world, researchers have long been trying to figure out how to unambiguously detect signs of life on distant exoplanets.
They are now one step closer to this goal, thanks to a new remote-sensing technique that relies on a quirk of biochemistry causing light to spiral in a particular direction and produce a fairly unmistakable signal. The method, described in a recent paper published in the journal Astrobiology, could be used aboard space-based observatories and help scientists learn if the universe contains living beings like ourselves.
In recent years, remote-life detection has become a topic of immense interest as astronomers have begun to capture light from planets orbiting other stars, which can be analyzed to determine what kind of chemicals those worlds contain. Researchers would like to figure out some indicator that could definitively tell them whether or not they are looking at a living biosphere.
For instance, the presence of excessive oxygen in an exoplanet's atmosphere might be a good hint that something is breathing on its surface. But there are plenty of ways that nonliving processes can generate oxygen molecules and trick remote observers into believing a world is teeming with life.
Therefore, some researchers have suggested looking for chains of organic molecules. These living chemicals come in two arrangements — a right-handed and a left-handed version that are like mirror-flipped images of each other. In the wild, nature produces equal amounts of these right- and left-handed molecules.
"Biology breaks this symmetry," Frans Snik, an astronomer at Leiden University in the Netherlands and co-author of the new paper, told Live Science. "This is the difference between chemistry and biology."
On Earth, living creatures select one molecular "hand" and stick with it. The amino acids that make up the proteins in your body are all left-handed versions of their respective molecules.
When light interacts with long chains of these different-handed arrangements, it becomes circularly polarized, meaning that its electromagnetic waves will travel in either clockwise or counterclockwise spirals. Inorganic molecules won't generally impart this property to rays of light.