In search of life in the universe

M.V.N. Murthy, The Institute of Mathematical Sciences, Chennai

Are we alone in this universe? For centuries this question has been asked and scholars have speculated that other worlds must exist containing life in some form. Recent experiments and discoveries have brought us to the threshold of finding answer to this old question.
As far as we know, with in our own solar system, life exists only on earth which is a planet. So the search could begin by asking the question "are there other planetary systems similar to the solar system in the Universe?". However planets are small and distant and cannot be observed directly.
Exo planets
The first discovery of a planet orbiting a star similar to the sun was made in 1995 by a Swiss team, Michel Mayor and Didier Queloz when they announced the presence of a planet similar to Jupiter orbiting the star 51 Pegasi, about 50 light years from earth.
Since this discovery, to date, about 429 planets and about 362 stars with planets have been found. None of these planets is an earthlike planet but resemble a hot Jupiter-like planet.
Given the size of the universe, therefore, it would not be a surprise if we find an earth-like planet in the near future. Suppose we do, then the next bigger question is "is there life on that planet?" That is, life as we know it, which starts from DNA and cells, and evolves to more complex forms.
The building blocks for creating primitive life forms do exist, in giant molecular clouds. Therefore can cells, bacteria and other micro-organisms be detected outside earth?
Panspermia
There are many hypotheses about the origin of life; one such is the Panspermia (meaning seeds of life in Greek) Hypothesis. According to this hypothesis "seeds of life" exist already all over the Universe and life on earth may have originated through these seeds. This is not a new hypothesis as the term was first mentioned in the writing of the 5th century BC Greek philosopher Anaxagoras.
While the idea found support in 19th century from the famous physicist, Kelvin, an objection was raised by Becquerel that such micro-organisms would not survive the cosmic Ultra-Violet (UV) radiation.
The micro-organisms are shielded from UV radiation on earth by the presence of earth's atmosphere. Can they survive in an environment where UV radiation is present?
In recent times, astrophysicists Fred Hoyle and Chandra Wickramasinghe have revived this hypothesis. Together, in 1978, they promoted the theory that life evolved in space, spreading through the universe via panspermia, and that the evolution of life on earth is driven by a steady influx of spores (spore is a reproductive structure that is adapted for dispersal which survives for extended periods of time in unfavorable conditions) arriving via comets.
Some of the organic material thrown off into space by comets are swept up by planets like Earth over millions of years. In fact, the Earth collects roughly 100 tonnes a day of such material mixed with meteorite dust. From an altitude of 70-100 km this dust settles through the middle atmosphere and stratosphere.
The existence of extra-terrestrial life in the vastness of the universe has also been the subject of investigation by Jayant Narlikar, a long time collaborator of Fred Hoyle. Given the immensity of the universe, Narlikar feels that the possibility of life, even the advanced type, may exist but attempts to contact such advanced extra-terrestials may be a long drawn-out procedure.
However, experiments conducted on our own atmosphere at heights where no living organism on earth could reach by any known mechanism may throw some light on the origin of extra-terrestial life forms.
Search for extra-terrestrial life
With this in view, in 2001, a team of Indian and British scientists led by Jayant Narlikar and assisted by Indian Space Research Organisation (ISRO) investigated air samples at different heights up to a maximum height of 41 km above earth, starting from about 21 km. This is significant since the maximum height to which the life forms on earth can be thrown into the atmosphere is approximately 21 kms. Such heights can only be reached by a severe volcanic erruption.
The experiment consisted of hoisting balloons from the Tata Institute of Fundamental Research (TIFR) Balloon facility in Hyderabad, carrying specially sterilised collectors. These collectors were opened at four selected heights to collect samples of frozen air existing at that height. The collectors were then closed and sealed before being brought back to earth.
At each height at least two or more collectors were opened to suck air. These samples were then analysed in sterile laboratory conditions. To be fool-proof, the samples were analysed independently in different laboratories.
Taking every possible precaution against contamination, cultures of the following micro-organisms were found: (a) The coccus (spherical bacterium), (b) the bacillus (rod-like) and (c) a fungus. These are not common contaminants, nor were they found in the lab which analysed these micro-organisms.
Another try
The second such experiment was performed in 2005. Air samples were collected from six heights bands: 20-24 km, 24-27 km, 27-30 km,30-35 km, 35-40 kms, above 40 kms. In all about 16 cylinders were sent up and two samples were collected from each height band. One cylinder was kept unopened to provide a standard reference. Analysis was done at the Centre for Cellular and Molecular Biology (CCMB) and National Centre for Cell sciences (NCCS) and the results were announced in 2008.
In all, 12 bacterial and 6 fungal colonies were detected. Of the 12 bacterial colonies, nine of them showed 98% similarity with known species. The remaining three strains were potentially identified as new species to be studied in greater detail. It was also significant that all three new species were found to be UV resistant.
The scientists involved in these experiments claim that it is very unlikely that these new species are laboratory contaminants since the control cylinder which was not opened in space did not yield any micro-organism when analysed. The greater UV resistance found in the three new species makes them possible candidates for interplanetary transfer, that is, they have come from outer space.
Of course, this intriguing possibility requires further confirmation.  Even if this possibility is ruled out, these pioneering experiments have demonstrated the existence of micro-life in our own atmosphere at heights where there were not expected to be any.
Based on the talk by Jayant Narlikar at IMSc