Why don't humans give up hopes on spotting intelligent extra-terrestrial life? Because we haven't got any categorical evidence which suggests that alien life is non-existent and until proven otherwise extra-terrestrials could exist. Though probability of intelligent alien life is an intensely debated topic, SETI (Search for extraterrestrial intelligence- collective name for a number of activities people undertake to search for intelligent extraterrestrial life) is in the lookout for an alien radio signal from outer space.

With no successful alien-spotting to boast about, SETI was going through a severe cash crunch due to dwindling interest of funding agencies and high profile individual donors. However, latest news from the institute will revive the lost interest, as it has announced raising $200,000 from a crowd-sourced fundraising effort that was launched earlier this spring. Setistars.org has a big red bold lettered message on the site, "Thank you for all your support to resume." 

"We are so grateful to our donors," said Tom Pierson, who co-founded the SETI Institute with Jill Tarter. "We believe we will be back on the air in September."

The failure of the SETI program to announce an alien radio signal had partially dimmed hopes of humans' encounter with life forms outside earth. The Allen Telescope Array (ATA) went offline in April this year following a SETI announcement about the lack of funding for the institute.  The Allen Telescope Array is a facility dedicated to detecting electromagnetic transmission from outer space.  

SETI had announced taking down ATA as the funds from NASA and a number of wealthy donors, including Microsoft co-founder Paul Allen, had exhausted and the institute needed an estimated $5 million to operate for the next two years.

O Alien, Where Art Thou?

Term 'extra-terrestrial life' refers to a hypothetical range of life starting from simple bacteria-like organisms to sapient beings which are far more advanced than humans. According to scientific research, celestial bodies with potential capacity to sustain life include Mars, Venus, Jupiter, Moons of Jupiter - Ganymede, Callisto, and Europa, and Moons of Saturn-Titan, and Enceladus.

SETI estimates the number of advanced civilizations that might exist among galaxies, by means of "Drake Equation" devised by Frank Drake, Emeritus Professor of Astronomy and Astrophysics at the University of California, Santa Cruz. Being intensely speculative, the equation arrives at tentative solutions by multiplying values like 'the number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable,' 'the rate of formation of stars suitable for the development of intelligent life,' 'the fraction of those stars with planetary systems,' 'the number of planets, per solar system, with an environment suitable for life,' and so on. (More on Drake Equation).

The major ambiguity about Drake Equation is that it assumes and completely relies on a speculative factor: According to the equation, the probability of life arising on suitably habitable planets (ones with water, rocky surfaces and atmospheres) is almost always taken to be 100 percent, says Space.com.

Claims and Counterclaims:

Andrei Finkelstein, top Russian scientist and director of the Russian Academy of Sciences' Applied Astronomy Institute, in June this year expressed hopes that extra-terrestrial life can be found in two decades. "The genesis of life is as inevitable as the formation of atoms ... Life exists on other planets and we will find it within 20 years," Finkelstein said while addressing an international forum dedicated to the search for extraterrestrial life. He remarked that 10 percent of the known planets circling suns in the galaxy resemble Earth. If water can be found outside of earth, finding life elsewhere isn't impossible, Finkelstein added.

Finkelstein's institute runs a program launched in the 1960s at the height of the Cold War space race to watch for and beam out radio signals to outer space.

"The whole time we have been searching for extraterrestrial civilizations, we have mainly been waiting for messages from space and not the other way," he said.

Probability of Abiogenesis (method by which life on Earth arose):

Recent most study which ruled out the possibility of alien life was published last week, by David S. Spiegel of Dept. of Astrophysical Sciences, Princeton University, and Edwin L. Turner, of Institute for the Physics and Mathematics of the Universe, The University of Tokyo. In their research paper titled "Life might be rare despite its early emergence on Earth: a Bayesian analysis of the probability of abiogenesis" the researchers argue that the probability factor of abiogenesis varies from planet to planet, and a assigning a constant value for probability will only lead to biased solutions.