JOIN USWe can find out if bacteria are multiplying or a cancer is spreading by looking for the cells themselves or for tell-tale chemicals that arise along with them. But how do we find out if there is life on planets other than earth? Yes, we do look for life-bearing chemicals here too. But there is something huge that we are overlooking here. Sometimes, a planet can also support life that is very different from our perceptions, also based on chemicals purely.
A group of scientists at Ecole Polytechnique, Fédérale, Lausanne (EPFL) in Switzerland report in the journal, Proceedings of the National Academy of Sciences (PNAS), a method that depends on movement, rather than chemicals, as a sign of life. Giovanni Dietler, Sandor Kasas and Giovanni Longo, with Simone Ruggeri FS, Benadiba C, Maillard C, Stupar P and Tournuc H, make use of a see-saw, just
micrometres in size, to detect microscopic physical movement, as an indicator of growth or locomotion, from which they come to the conclusion that there is life in the sample being tested. They also determine how well drugs act in the pharmaceutical lab, or on the surface of a far-off planet.
Chemicals of life
The ingredients for life on earth are carbon dioxide, methane, water and oxygen. So, the traces of these elements anywhere else in the space could be taken as a first-rate indicator of life. We design space probes to analyse the soil and
atmosphere of different planets. Being on earth, we analyse the spectrum of the light that has passed through the planet’s atmosphere and look for the signs of chemicals on distant planets.
In a more detailed approach, we analyse the spectrum of infrared light (heat) that the planet radiates. As particular chemicals in the atmosphere absorb specific frequencies, we can make out that these chemicals were present in the
location. The mix of the signature chemicals on the earth has changed over the ages, as life evolved, from single-celled creatures, to plants, dinosaurs, birds and mammals. Finding signature chemicals on a planet would hence indicate both a strong possibility of life, as well as the state of evolution.
Of course, all this is based on the assumption that any form of life on the other planet is also majorly based on carbon and oxygen. But we can’t overlook the possibility that there could be other forms of life, which would lead to the
build-up of a mix of varied chemicals. In principle, there could be organic-type
molecules based on silicon too. Not that it is likely, as a silicon-based life would need to exist at high temperature and metabolic processes would need to be different. But there could be other chemical bases for self-replicating organisms that resemble life.
And then, even if the life forms were similar to those on the earth, there could be different avenues of circulation of nutrients and by-products without signature chemicals in the atmosphere. Thus, this clears the belief that although finding the right chemicals on a planet would be a strong indicator of life, not
finding them wouldn’t mean the absence of the same.
Yet another indicator of life could be the reason for a planet to have a smooth and undulating topography, as opposed to jagged and rocky one. Studies of soil erosion and movement of landmasses on the earth have shown that while rivers, rainfall, winds do cause the break-up of rocks, the chief cause of creating loose, transportable soil, which moderates discontinuities in the landscape are biotic, or biologically-driven processes, like animal burrowing, growth of roots and microbial actions. These effects also fall in step with the timing of seasonal temperature variations and there is a mutual support of the life forms and the topography.
Detecting movement
The Lausanne scientists sidestep the uncertainties of chemicals and topography and have adapted the existing atomic force microscope to sense motion at the scale of the activity of bacteria. This would hence be detection of direct and non-chemical signs of life.
The idea is that if there are living things, then they can be expected to move – either move some limb or carry out a biological process (feeding, excretion or growth). If there can be a sensitive way of detecting this motion, then we would be able to find unmistakable signs of life on any planet.
The atomic force microscope is tiny protrusion, like a spring-board, just micrometres in dimensions that swings free from a holder. The protrusion is like a lever fixed at one end, or a cantilever. At the free end, there is a tip of the order of nanometres, which protrudes down to scan the surface being examined.
Unevenness of the surface causes the lever to move up or down and the movement is detected by a laser beam that reflects off the lever. The arrangement is able to sense undulations of fractions of a nanometre.
In the adaptation by the Lausanne group, the cantilever is moved not by forces that push the tip from below, but by movement of bacteria that are deposited on the lever itself. In trials carried out, the dimensions of the arrangement allow about 500 bacteria to perch on the lever. Movement of even a few of them affects the load on the lever and it swings up or down – to be detected by the laser beam sensor. Over a period of time, the printout of the laser beam trace can reveal if there is any movement going on in the culture on the lever.
“The system has proven accurate for detecting bacteria, yeast, and even cancer cells,” a press release from EPFL says. The arrangement can immediately be used in the testing of different drug preparations, all at the same time. An array of cantilevers could be covered with bacteria or cancer cells and different drug compounds could be applied, each to one of the cantilevers.
Where the drugs seem to work, bacteria or cells would be rapidly killed off and there would be decrease and cessation of the movement. Effective drugs would then be identified quickly, conveniently and this would speed up drug development.
The same arrangement could also be made part of the test equipment of crafts that are sent out on missions to planets or comets. “As it relies on motion rather than chemistry, the cantilever sensor would be able to detect life forms in mediums that are native to other planets such as methane in the lakes of Titan,” the press note says.