Jay Nadeau of McGill University discussed submersible microscopy for microbial detection and classification at the 2012 Canadian Space Summit with the thought of future applications for earth observation and potential and Jovian satellites missions.
Abstract: Extraterrestrial life in our Solar System is almost certain to be microbial. Methods and technologies for unambiguous detection of living or extinct microorganisms are lacking and thus critically needed for lifedetection missions. The most likely environments for the evolution and persistence of life are those with liquid water, for the obvious reason that all known life requires liquid water to survive. The best candidate areas for significant extant life on other planets are seas, lakes, ponds, and rivers, and the discovery of any extraterrestrial body of water is of great interest to astrobiology. One of the most exciting astrobiological discoveries of the century was the Galileo mission’s measurement of induced magnetic fields close to the surface of the Jovian moons, which implies large subsurface salty oceans. The surface features of Europa are also consistent with this model. As a result of this finding, these moons, particularly Europa, have become key targets for both orbiter and lander missions for the next several decades. A lander mission requires an autonomous underwater robot of the sort conceived over a decade ago as a “Hydrobot” swimming robot and developed since into a concept for an autonomous ice penetrator/ swimming robot. The robot would be equipped with an array of lifedetection instruments that must be lowmass, lowpower, robust, and autonomous.
With these goals in mind, we are developing robust technologies for the detection and identification of micronscale organisms at low concentrations in complex liquid media. Along with being crucial to astrobiology, these techniques are also at the heart of many other fields such as environmental and medical microbiology and food safety. The best method for microbial enumeration on Earth is specific labelling of the organisms with fluorescent dyes followed by highresolution light microscopy. However, light microscopy is difficult to develop for space or even extreme environments on Earth, as the instruments are extremely fragile, their light sources demand high power, and their operation requires the continuous input of an expert. An alternative to traditional imaging microscopy is holographic microscopy, which is capable of threedimensional imaging of the entire volume in the field of view with a single detector frame. Holographic microscopy works by illuminating the object of interest with a point source of coherent light. The light is diffracted around the object, and also phase shifted through it in the case of a translucent object. These perturbations of the beam result in a diffraction pattern forming at the detector that contains information about the location and optical properties of the object. Our design incorporates two innovations: wireless data relaying and the use of a reference beam, making detection in thick or turbid media possible.
These new approaches are highly promising for Earth applications and for space. The eventual microscope will be a small, robust, handsfree device that can be placed into a pond, river, lake or sea and left for at least several hours, limited by battery power and hard drive capacity. The data will show detailed morphology and motility behaviour of any organisms present in the sample, and distinguish “meaningful” motility from drift, currents, and Brownian motion. It will be useful for sites of microbiological interest and for characterization of drinking water, wastewater, fluids in food processing, and other sources. For space applications, the low weight and low power requirements of our instrument mean that several may be deployed in a single mission, maximizing the chances for success. The unambiguous nature of the biosignatures also makes these technologies highly compelling for use in life detection. The use of motility as a biosignature is a novel approach in astrobiology, but one that is very logical for underwater environments such as those expected to be found on the Jovian moons.