Enceladus is the sixth largest satellite of Saturn at about 500 km in diameter, about one-tenth that of Titan, the largest Saturnian satellite, and is one of the strong candidates for hosting some form of microbial life.
To detect it, our best option might be a technique called digital holographic microscopy , which uses lasers to record 3-D images.
Enceladus has a lot of water, in an ocean hidden under an icy shell that covers the entire surface. How to find microbial life in such conditions from Earth? As explained by Jay Nadeau , a research professor of aerospace and medical engineering in Caltech’s Division of Engineering and Applied Sciences, one of the authors of the procedure who has published in Astrobiology :
It is more difficult to distinguish between a microbe and a dust particle than one would think. It is necessary to differentiate between Brownian motion, which is the random motion of matter, and the intentional, self-directed motion of a living organism.
Nadeau refers to detecting life in geysers, huge geysers that expel water vapor through cracks in the icy shell of the moon, and that regularly burst into space. The jet of water in space offers a rare opportunity, Nadeau says, to send a probe past one of the jets and collect water samples.
Once that milestone was achieved, a range of questions would be raised: if samples are collected, how could they be identified as living cells? Some strategies for showing that a microscopic speck is actually a living microbe involves looking for patterns in its structure or studying its specific chemical composition.
Looking at the patterns and the chemistry is helpful, but I think we need to take a step back and look for more general characteristics of living things, such as the presence of movement, that is, if you see an E. coli, you know that it is alive (and not , say, a grain of sand) by the way it moves.
To study the movement of microbes, Nadeau proposes the use of an instrument called a digital holographic microscope that has been specifically modified for astrobiology. In digital holographic microscopy, an object is illuminated with a laser and the light that bounces off the object and is directed back to a detector is measured.
This scattered light contains information about the amplitude (intensity) of the scattered light and about its phase (a separate property that can be used to indicate the distance traveled by the light after being scattered). With both types of information, a computer can reconstruct a three-dimensional image of the object, which can show movement through all three dimensions .