In The Beginning -- Bug-Eyed Monsters
Remember the flood of science fiction movies in the 50s? It ushered in wide ranging interest and speculation about aliens from other worlds, an interest that's still very much alive today.
But that speculation didn't start in the 1950s. Sci-fi serials were produced for movie houses in the 30's and 40's, and writings of Edgar Rice Burroughs considered inhabitants of Mars at the turn of the 19th century. Before that, astronomers of old could see the moon, and even with the naked eye imagine that the dark, flat areas were seas, perhaps sailed by a lunar civilization.
Mars was always a first choice for imagined aliens, once astronomy established some of its characteristics at the end of the 19th and beginning of the 20th centuries. It was found to be about 1/2 the size of earth, tilted on its axis only about a degree-and-a-half differently than earth, with a day nearly the same length as an earth day.
The Draw Of Mars
At that time of great discovery, made possible by the great refracting telescopes of the age like the massive 40 inch refractor at Yerkes Observatory, the Italian astronomer Giovanni Schiaparelli viewed what he called canali, which translates to English as channels. But some astronomers, like Percival Lowell extrapolated the idea to that of canals, which he believed were dug and used by a Martian civilization.
Some other astronomers agreed, and many drawings of the canal system were made by Lowell and others. It was also observed that during the Martian year the prominence of the canals seemed to wax and wane, possibly in relation to the melting and re-freezing of the polar ice caps. A convincing story of intelligent water use existed until well into the 20th century, though many astronomers were unconvinced.
Satellite photos sent back by the early Mars Mariner spacecraft showed no existence of canals whatsoever -- or any evidence of civilization or even life, for that matter. The photos transmitted back in the mid 1960's showed a barren planet, heavily cratered like our own desolate moon. There were polar caps to be sure, but these were found to contain more frozen carbon dioxide that water, so the belief in Martian life was dealt a severe blow.
Where Are The Aliens?
Still, belief in the existence of alien life somewhere in our galaxy remained strong. It seemed that with some 200 billion or more stars in our galaxy, there had to be life out there somewhere. Yet the absence of any real evidence caused Enrico Fermi and Michael Hart to postulate the Fermi-Hart Paradox.
Given that our galaxy is much older than earth, it seems that many other life-producing planets -- if they exist -- could be much older than earth, and have space travel capabilities perhaps millions of years more advanced than our own. But -- there is no tangible evidence that aliens have ever come to our planet to give us greeting. The Ferim-Hart Paradox basically asks: "Where are they?" And truly, we have no real evidence that alien life is out there.
The Drake Equation
Adding that to the Mars canal bust certainly deflated many wishful believers. Yet this did not dismay Charles Drake, who proposed what has become known as the Drake Equation. The Drake equation combines a string of numbers and probabilities together to mathematically predict the number of concurrent civilizations in our galaxy. The parameters in the equation are our best guess values based on current research. You can try your own predictions using the Drake equation at Little Green Men. Based on best parameter measurements, predictions range from a few to as many as 1000 concurrent civilizations existing in the Milky Way.
The Drake equation doesn't run headlong into the Fermi-Hart Paradox primarily because the equation assumes that technical civilizations do not necessarily last that long, astronomically speaking. No doubt the fact that the equation was proposed during the height of the cold war helped formulate that belief. Our current inability to solve problems without war and even agree that there is global warming certainly does nothing to stretch those conservative civilization lifetime numbers.
The Mars Viking Mission -- A Failure?
None-the-less, optimism is difficult to squash, and in the 1970's the U.S. sent two Viking spacecraft to Mars to look for life. No longer were civilizations expected, or even visible plant or animal life. The Mariner pictures pretty much put that level of optimism to rest. But there were things about Mars that Mariner did reveal that still gave hope.
The Mariner program showed evidence of ancient flood channels on Mars. Not the canals of Lowell, but long dead and dry channels that had at least at some point in the past been flooded with a lot of water. Maybe millions, perhaps billions of years ago, but still flooded with water. This suggested that at least for a few million years of its early existence, Mars had all the ingredients that should have been needed to allow life to develop. A moderate temperature, a thicker atmosphere, and liquid water.
After that period of time, things went badly on Mars, with the atmosphere thinning out, water freezing, and the surface of the planet becoming dry, dry, dry. That change apparently was so fast on astronomical time scales that complex life apparently couldn't get started. But perhaps microbial life did.
So the Mars Viking program intended to find out, with two craft at two different locations, each with the ability to perform life and organic material search experiments.
The Viking probes ran experiments to determine if Mars had current life, and if existing organic material was in the soil. You can read more about the experiments at Discovery.com. A more detailed report about the metabolic discovery test, called the Labeled Release experiment, can be found at Factoids.
The Labeled Release experiment involved feeding nutrients to a sample of Martian soil and looking for signs of metabolism. The experiment gave a resounding positive result. Of course, that result could have simply been a chemical reaction between a possible exotic Martian soil and the nutrient. So the soil was heated, and then the test was performed again. The assumption was that if microbes were causing the result, the heat would kill the microbes, and the rerun would give a negative result.
But an experiment designed to search for organics in the soil gave a negative result. A third experiment to look for signs that some introduced gases being metabolized also failed. So the conservative position to take was to assume that no life or organic material had been found on Mars.
The Rise Of The Phoenix
But then came the Mars Phoenix Mission. It landed on Mars in 2008, some 30 years after Viking. It was sent to land in the Martian arctic region to explore the water history of Mars. It found the anticipated solid evidence for water ice on the planet, but also found that the soil had perchlorate in it. This had far reaching implications about the Viking experiment ran 30 years before.
It turns out that the organic search experiment of Viking would have been contaminated if perchlorate was also in the sites of the Viking craft. And if that was the case, the Discovery.com article says that perhaps organic material was discovered on Mars by the Viking missions. Coupled with the Labeled Release experiment results, the possibility of having discovered life on Mars in the 1970's greatly increases.
Reaching Out With SETI
Which brings us to the SETI Mission. Rather than search for primitive live on other bodies of our solar system, in the 1980s SETI started searching for intelligence generated radio signals from space. The idea was that an advanced civilization may send radios messages into space in an effort to establish communications. Certainly an advanced civilization would likely at least generate radio signals for its own use. In either case, it was considered possible for properly designed radio telescopes on earth to pick up such radio signals generated from afar.
Some in the astronomical community thought that the SETI mission was a bit premature, since we were not yet sure that many earth-like planets existed. At that time, the only known planets outside of our solar system were gas giants, many far too close to their parent stars to have hospitable conditions even had they been earth-like.
But with the launch of the Kepler Mission, some of that complaint has been answered. There have been planets found that are near earth size, although those so far discovered are too close to their parent stars. But planets have been found in the life zone -- the zone where a planet may have liquid water -- though as yet those planets so far discovered are gas giants. But one promising truth has been emerging -- stars with planets are commonplace. So the idea of SETI is not far fetched.
Thus far, the SETI effort has detected no definitive indication of extraterrestrial intelligence. But there are many many stars, and even with 1000 concurrent civilizations spread among them, it could take a long time to stumble upon an alien generated radio signal. Yet, it might occur any time -- so stay tuned.
I've always been interested in the possibility of extraterrestrial civilizations, having been an avid science and science fiction reader since grade school. But like all of a similar ilk, I'm disappointed that thus far, no proof of extraterrestrial civilizations is yet in hand. I tried to sum up this anticipation and disappointment with a humorous astronomy Limerick, which I've place on a few products at my Keen Designs store, in association with Zazzle.