One of the biggest questions of our time is "are we alone in the Universe?". Since the middle of the 20th century we've been hunting, without success, for any indications that life exists beyond the narrow confines of Earth's atmosphere.
One of the most promising places to look is Saturn's moon Enceladus, which has a deep ocean below an icy surface. When the ice cracks, Enceladus' weak gravity means that massive plumes of water vapour shoot out into space.
It's in these plumes that researchers hope to find the first living extraterrestrial microbes, and space scientists are hoping to one day send a probe through those jets to collect water samples that could be analysed for life. But a major question is how those living cells could be identified remotely.
Now, astrobiologists from Caltech – The California Institute of Technology – have gone all Star Wars and proposed using lasers and holograms. More specifically, they've proposed using a technique called holographic microscopy, where lasers are used to record 3D images.
"The hardest thing about bacteria is that they just don't have a lot of cellular features," said Jay Nadeau, a research professor of medical engineering and aerospace in Caltech's Division of Engineering and Applied Science. "Sometimes telling the difference between them and sand grains is very difficult."
Presence of motion
So rather than identifying by shape or structure, Nadeau and her colleagues suggested looking for more general characteristics of living things instead – like the presence of motion, for example. "That is, if you see an E. coli, you know that it is alive – and not, say, a grain of sand – because of the way it is moving," she said.
Holographic microscopy works by illuminating an object with a laser and then measuring the light that's bounced back. By doing so, a 3D image – hologram – of the object can be reconstructed that shows movement in all three dimensions.
In testing on samples of water from the Arctic ocean, her team was able to identify organisms with population densities similar those in the most extreme environments on Earth. The system can test a lot of samples quickly, and has few moving parts, making it ideal for astrobiology, she said.
"Digital holographic microscopy allows you to see and track even the tiniest of motions."