Although hard evidence for this has not yet been found, most cosmologists tend to believe that some form of life is bound to exist somewhere in the universe. This belief rests on the fact that there are about 3 to 5 x 1022 stars organized in about 800 billion galaxies in the observable universe. One such star is our Sun with its own planetary system. So, the number of planets is huge. There remains a very significant possibility of life existing somewhere else. The exact form of life that can exist is a matter of speculation – it need not be carbon and oxygen-based like it is on earth. Moreover, these life forms may or may not have evolved intelligence, as we know it.
Scientists look for extra-terrestrial life through various methods. According to latest research, the observable universe has a diameter of 92-96 billion light years. A light year is the distance traveled by light in one earth year. It is about 846 billion kilometers. Mankind’s present level of scientific and technological expertise is rather limited in the face of these distances.
The search for extra-terrestrial life is mainly based on checking radio signals coming from all over the universe for any form of signals. Since one does not know what kind of signal another civilization will be sending, the search consists of eliminating known types of signals and looking for anomalies or clusters that could only have been created intelligently. Thousands of scientists and volunteers working from personal computers help by analyzing data pouring in from outer space looking for the elusive signals.
Besides, there have also been attempts to send specific types of signals in the hope that a sufficiently advanced civilization would ‘read’ them and respond. Some scientists have also been sending and looking for laser beams. All this effort is directed at life forms that are technologically capable of receiving and sending wave signals and not ‘primitive’ forms like our bacteria and viruses.
An attempt to estimate the number of technological civilizations that might exist in our galaxy has been made by Dr. Frank Drake. It identifies specific factors thought to play a role in the development of such civilizations. It is a generally accepted tool used by the scientific community to examine these factors. The Equation is expressed as : N = R* × fp × ne × fl × fi × fc × L Where, N = The number of communicative civilizations The number of civilizations in the Milky Way Galaxy whose radio emissions are detectable. R* = The rate of formation of suitable stars The rate of formation of stars with a large enough "habitable zone" and long enough lifetime to be suitable for the development of intelligent life.
fp = The fraction of those stars with planets The fraction of sun-like stars with planets is currently unknown, but evidence indicates that planetary systems may be common for stars like the.
ne = The number of "Earths" per planetary system All stars have a habitable zone where a planet would be able to maintain a temperature that would allow liquid water. A planet in the habitable zone could have the basic conditions for life as we know it.
fl = The fraction of those planets where life develops Although a planet orbits in the habitable zone of a suitable star, other factors are necessary for life to arise. Thus, only a fraction of suitable planets will actually develop life.
fi = The fraction life sites where intelligence develops Life on Earth began over 3.5 billion years ago. Intelligence took a long time to develop. On other life-bearing planets it may happen faster, it may take longer, or it may not develop at all. fc = The fraction of planets where technology develops The fraction of planets with intelligent life that develop technological civilizations, i.e., technology that releases detectable signs of their existence into space.
L = The "Lifetime" of communicating civilizations The length of time such civilizations release detectable signals into space.
On the other hand, the search is also on for potential locations where life could exist, at present or even in the past. Thus the recent discovery of a ‘super earth’ near the red dwarf star Gliese 581, which is about 20.5 light years away, caused considerable excitement because it had some climatic conditions similar to our planet.
About life in our solar system, several potential locations have been speculated upon, including the satellites (or moons) of these planets. Evidence for recent rivulets has been found on Mars indicating existence of flowing liquid. But this could be either water or carbon dioxide. Carl Sagan proposed that floating animals could survive on Jupiter – provided they had an ammonia-based metabolism.
However, scientists hold out more hope for the moons of other planets – like Europa, Ganymede and Callisto, the three largest moons of Jupiter, and two of Saturn’s moons, Titan and Enceladus. Besides looking for life forms or even conditions conducive for life on the planets and their moons, scientists are also examining meteorites in case some trace of life forms from the past has survived on them.
What can happen if there is an encounter with extra-terrestrial life depends largely on the nature of that life form. In all probability, such life would be adapted to completely different circumstances. However, if it has evolved, like humanity, developed intelligence and become technologically superior then either man could benefit from it or be destroyed by it. On the other hand, a primitive form of life could be a cause of unwitting damage.
However, the proof of existence of such life would be a giant leap forward in man’s quest for understanding several scientific and philosophical questions.