Page:Concepts for detection of extraterrestrial life.djvu/49

 CHAPTER X

When Professor Wolf Vishniac conceived a device to search for life in space it was inevitable that his biologist friends would name it the “Wolf trap.” The original Wolf trap was built to demonstrate on Earth the feasibility of detecting automatically the growth of micro-organisms on Mars. When operated either on the laboratory floor or outdoors, the feasibility model signals bacterial growth within a few hours after activation.

The heart of the Wolf trap is a growth chamber with an acidity (pH) detector and a light sensor; the former senses the changes in acidity which almost inevitably accompany the growth of micro-organisms, while the latter detects changes in the amount of light passing through the growth chamber. Micro-organisms, such as bacteria, turn a clear culture medium turbid (cloudy) when they grow. It is the change in turbidity which the light sensor measures. The pH measurement complements the turbidity measurement by providing an independent check on growth and metabolism. When either or both of these changes occur, the sensors can communicate this information to a telemetering device which in turn relays the results back to Earth.

The reason for first searching for micro-organisms on Mars is that even in the absence of higher plants and animals, the basic ecology (the interactions between the organisms in a biological community) would not be changed; it is possible to maintain a planetary ecology by micro-organisms alone, though not by animals and higher plants in the absence of micro-organisms.

The biological reasoning behind the particular approach of the Wolf trap was presented by Professor Vishniac as follows. All of the organisms of an environment must have a source of raw materials and energy for growth. Some, like the green plants, can use light energy to manufacture energy-rich chemicals (food); this process is named photosynthesis. Others, like humans, must consume either the photosynthetic plants, or animals which subsist 39