The fancy that extraterrestrial life is by definition of a higher order than our own is one that soothes all children, and many writers. ~ Joan Didion
If a group of reasonably science-aware folks were forced to list the Big Questions in science, we might come up with a disparate listing, but there are two questions that I suspect would make everyone's list. First is the origin of the universe. Probably every human being who ever lived has pondered this question because we all want to know where we came from. Even the most fundamentalist Jew, Muslim, and Christian have at some time in their lives considered alternative ideas for this greatest of all events.
The other question that would make everyone's list is whether life exists elsewhere in that same universe. Of course, the dream of many (and nightmare of some) is that we might someday find a species with which we can communicate (something we don't so well with each other), but most of us would be perfectly happy to find some tiny microbes wriggling about in the sands of some distant world.
In recent years, the question has become less theoretical because, as we launch more and more satellites and probes, we find more and more tantalizing hints that life could exist on other worlds in our own solar system. The possibilities have generated a lot of discussion of late.
For instance, a German scientists by the name of Joop Houtkooper has announced that the Viking Landers, which arrived on Mars in 1976, may have found life after all. He says the lander data shows signs of hydrogen peroxide. His little bugs would have been filled with a combination of hydrogen peroxide and water, providing them with a natural anti-freeze. As much as 0.1% of Martian soil could be of biological origin, a ratio comparable to what one finds in Antarctica, where, last I checked, it's bloody cold.
Of course, other scientists disagree, but there arguments are based pretty much on the old "life on Earth doesn't work like that." They also base their opinions on the gas chromatograph results. The trouble with that is that some intrepid scientists have determined that the GCMS may not been accurately set up for the conditions on Mars. They based their opinion on the fact that the instrument was unable to find life on another planet -- Earth.
As someone once put it (it may have been Carl Sagan), it would have been so much easier if a Martian giraffe had walked by the cameras. Or if the rovers would send back a snap like this:
Life is also more tenacious than we generally credit. One of the continuing objections to life on Mars is that it's bathed in radiation (besides being colder than an intergalactic welldigger's ankles). That sounds like a real killer until you remember that the Apollo 12 crew brought back a camera full of terrestrial microbes from an old Surveyor probe, microbes that were resuscitated. Some scientists think the contamination occurred after the camera was returned, but, considering that we keep finding life on Earth where we aren't supposed to find it (salt flats, suboceanic smokers, and so on), the possibility that microbes can survive the harshest conditions is certainly not far-fetched.
The problem is that most people tend to think of "life as we know it." That is, life should be carbon- and water-based. Intelligent life should be bipedal with binocular eyes. Well, that's life as we know it. Except that some very intelligent life on Earth (whales and dolphins) is not bipedal. If we can be that far off for life we see all the time, how wrong might we be about other life forms?
Recently it seems that scientists are trying to think outside the carbon-based box. Maybe DNA is not the be-all and end-all. Maybe Titan holds ammonia-based bugs. And maybe inorganic compounds can generate life. Perhaps Spock's green blood isn't so unlikely after all (well, it might be, since it would make for an inefficient transfer of oxygen).
The point is that scientists are beginning to speculate about life as we don't know it. That opens a major can of worms (or microbes) because it raises a thorny question. If we're looking for life as we don't know it, how will we know it when we find it? It means we need to reconsider the factors that make something "alive".
And, if we aren't sure of what's alive, can we be sure we would recognize intelligence if we saw it? (Insert sarcastic joke here.) Most people expect that intelligent beings will have artifacts, cities, spoken language, and so on. But what if we came across a highly intelligent group of ... well, whatever... that communicated through color, perhaps in ranges like the ultraviolet, that we can't even see.
The Discovery-Science axis did some imaginative programs a while back speculating on life on other worlds. They did seem to be fascinated by creatures that floated, but if you can get beyond that, the flights of fancy taken by the scientists involved showed that entirely alien ecosystems could operate logically. And they stayed within the carbon and water framework.
I suspect that we're going to find strong evidence of life within my lifetime (assuming I don't get run over by a truck tomorrow). It may be microbial, it may be swimming in the oceans of Europa, or it may be breathing methane and crawling around on Titan. But, I do think we'll find something.
I just hope we'll recognize it when we find it.