“Is there life on Mars?” This must be one of the most-asked questions in astronomy. In this article I am going to look at the historical background to this question. Current thoughts on the possibilities of Martian life will be considered in a follow up article.
Why is life on Mars even regarded as a possibility? Even two hundred years ago, it was obvious that Mercury was so close to the Sun that it must be a dried up cinder, while Jupiter and the planets beyond it were so cold as to be incapable of hosting life. Only Venus and Mars were potential homes for creatures like ourselves. The Venusian surface was obscured by unbroken clouds, so astronomers imagined it to be inhabited by dinosaurs and sea monsters and no one could prove them wrong. The Martian surface could be seen through the crystal-clear Martian atmosphere, revealing intriguing features, and astronomers could try to predict conditions there.
Briefly Mars is just over half the size of Earth, its day is about 24 hours 40 mins long and its year is 686 days long. We now know that the planet’s carbon dioxide atmosphere is extremely thin (only 1/100th of the pressure at Earth’s surface) and −5 °C is the average temperature on a nice day. Compared to Mars, even P*******n on a wet winter’s day looks inviting . However once upon a time the Martian deserts seemed more welcoming…
Scientific thinking about life on Mars began in the late 1700s when William Herschel (1738-1822) observed that Mars’ polar caps shrunk in the planet’s summer and grew back in the winter. Clearly the ice was melting and refreezing with the seasons, but what was happening to the water between thawing and freezing? Italian astronomer Giovanni Schiaparelli (1835-1910) had a possible answer. In 1877 he reported observing long straight features on Mars. He called these “canali”, meaning “channels” in Italian. This word was mistranslated into English as “canals” (mistakes like this common at this time as Babel Fish would not run very efficiently on the steam-driven Victorian internet’s Babbage Engines).
Bostonian Percival Lowell (1855-1916) had a rich life as business man, diplomat and author, but he was also an astronomer. However he was not a Proper Astronomer being a mere amateur. However Lowell didn’t care a jot about professional star-gazer’s opinions as he was extremely rich. Appropriately enough when you consider his other great astronomical interest, searching for a trans-Neptunian planet, he was a plutocrat. In fact he was so wealthy he founded his own observatory complete with 24 inch telescope near the high altitude and then remote town of Flagstaff, Arizona, chosen for the excellent observing conditions. (He may have had other reasons to retreat from Boston, it appears that Lowell had a sort of Niles–Maris–Daphne thing going on with Constance, his formidable battleaxe of a wife, and the observatory’s understanding secretary Wrexie Leonard.) Since the observatory was his own he could do what he wanted there and until his death he churned out maps of the elaborate Martian canal network (he counted 437 individual canals) and discussed his observations of the planet and his theories on its inhabitants in hugely popular lectures and a series of books. Basically Lowell established the idea of life on Mars in the popular imagination. And how! Mars, he said, was a dying world, losing its atmosphere and water. The planet’s advanced inhabitants (tall, dignified humanoids who probably dressed in togas) were responding to this crisis by irrigating their crops with water from the polar caps distributed via the canals. The public lapped this up, and it inspired authors to use this wonderful background in their stories.
Ah, was there ever a more romantic myth than the pre-Space Age Mars with its canals crisscrossing vast and ancient dry seabeds haunted by ghosts and brigands, of towering crystalline cities where the beautiful but decadent and dying Old Martians linger on. Meanwhile monstrous octopods in their tripedal war machines slowly and surely draw up their plans for conquering Earth. Inspired by Lowell, this lingering vision was created and maintained by several prominent authors such as Wells, Burroughs (Edgar Rice, not William), Bradbury (Ray, not Malcolm) and Brackett (Leigh not Dame Hilda).
All fantasy of course. The idea of Mars being habitable to creatures like ourselves was already on very shaky ground when Lowell’s speculations were at their peak. Spoilsport scientists pointed out that spectroscopic examination of the planet’s atmosphere had found no sign of water vapour, for that matter the atmosphere was too thin to allow large bodies of liquid water to exist. Also there was the failure of observers outside Lowell’s circle of sympathizers to see the canals, nor could the canals be photographed. This was of course because they did not exist, sadly Lowell was deluding himself (and so he is now often described in histories with words like “buffoon” and “mountebank”, as a genuinely gifted observer and theoretician – when he wasn’t looking at Mars- he deserves to remembered better).
Lowell (and the public) ignored the criticisms, but most scientists lowered their expectations. Gone were the great Martian civilizations, yet great expanses of vegetation, weirdly adapted to the harsh climate, were still thought likely and perhaps there were alien arthropods nibbling on their leaves. The evidence for this idea was the “Wave of Darkening”. This was a well-observed phenomenon when the dark areas visible on the planet’s surface through even amateurs’ telescopes got darker in their hemisphere’s summer. The only possible explanation was that the dark areas were masses of vegetation, possibly mosses or cacti, bursting into a lush growth period as the temperatures rose. To reflect this, these areas were usually depicted as bright green in artists’ impressions of the planet. The areas without vegetation were covered in gently rolling dunes of orange sand. The planet’s surface was cold, and the atmospheric pressure there approximated that at the summit of Mt Everest. Humans could probably survive there wearing fur coats and breathing through oxygen masks, or at worst a goldfish bowl over their heads.
This vision of Mars persisted widely until the early 1960s. The older library books in the primary schools I attended in the 1970s all described life growing and crawling across the Martian plains as a certainty. This vision was accepted even by experts. A 1959 report for the US government claimed that “there is rather good evidence that some indigenous life forms may exist” on the planet. Even more startling was the report on the first NASA-sponsored feasibility study for a Mars landing (carried out in 1963) which called for one of the first three men on Mars to be a biologist, who would evaluate the landing site for “unfriendly life forms.” Any local lifeforms unfriendly or benign would be assessed for “for possible nutritional value.” (Gulp!)
We said goodbye to this view of Mars as a cradle of life and potential larder in July 1965 when Mariner 4 spoiled the fun! Mariner 4 was the first spacecraft to successfully reach Mars, With what would now be regarded as a laughably primitive camera it took 21 images and transmitted them to Earth. There was not a canal to be seen. The surface appeared barren and as cratered as the surface of the Moon. Hopes that we would find anything living on Mars dropped to an all time low. Mars, it seemed, was as dead as the Moon.
These hopes rose again when Mariner 9 arrived at Mars in 1971 and returned hundreds of images of all regions of the planet’s surface. Some showed enormous extinct volcanoes and evidence of enormous seasonal dust storms (these storms proved to be responsible for the wave of darkening as they deposited light dust on the darker highlands in the autumn). The most amazing Mariner pictures showed what appeared to be dried up water courses. If the surface of Mars had once been even slightly damp, then simple life still seemed possible. In 1976 NASA attempted to prove this once and for all, when the Agency sent the two Viking space craft to land on the planet’s surface. For a first attempt at a Mars landing, these were an amazing success (virtually forgotten now are the USSR’s handful of attempts to reach the planet’s surface in the early 1970s; just one reached its destination intact, only to break down after 20 seconds). The primitive humans of the 1970s would drop to their knees in awe at the very sight of an Ipad or Ninento DS, yet these ancient people built and designed the Vikings, which represented very advanced technology. Clearly our ancestors were not the long-haired and dim-witted primitives of popular imagination. Either that or they had help from space aliens…
Both Viking 1 and 2 came to rest on plains that were much rockier than expected and entirely devoid of flora or fauna. Immediately the probes launched into a programme of photography and research into Martian meteorology, seismology, soil chemistry and biology.
The biology experiments and their results are still controversial today. Each Viking lander used its mechanical arm to scoop up Martian soil and deposit it into a sophisticated miniature laboratory on board the probe. The soil was tested in a number of ways to try to verify if it was home to a thriving culture of micro-organisms. One of the experiments involved feeding a rich nutrient ‘broth’ to the soil. Cunningly this “chicken soup for the soil” was laced with mildly radioactive carbon; in tests on Earth any earthly organism exposed to the food gobbled it up and ‘breathed out’ radioactive carbon dioxide. This was easily detected by the instruments on board each Viking. The premise was any Mars bugs in the soil would slurp up the food and the Viking would detect their satisfied after dinner burps. No such gaseous emanation would be expected from lifeless soil. What do you think happened?
Immediately after the broth was released, the test chamber swelled with carbon dioxide! Both Viking landers saw this. Was this proof of life on Mars? The mission scientists, no doubt trembling with excitement, ordered further experiments, and these caused doubts to rise. The initial belch of gas from the soil tapered off abruptly. If there were Mars bugs in the soil then they were not thriving on the food. Adding more broth did not spark a second release of gas, this never happened with terrestrial soils. There was one hopeful sign: when fresh soil samples were taken but baked at high temperature in the probes’ tiny ovens before adding the nutrients, nothing happened. This result is just what you would expect if the heat had sterilised the soil, killing its microscopic inhabitants. It was another experiment which caused the final disappointment. When the Mars soil at the two Viking sites was analysed for organic molecules, the stuff any feasible living thing would be made of, none was found. The soil was sterile; unbelievably there was more organic material to be found in the lunar soil brought back by the Apollo missions.
Hence the Viking experiments were less than conclusive. It appeared that the soil on Mars had some very peculiar chemical properties (it appeared to contain a powerful oxidising compound similar to hydrogen peroxide) but was lifeless. Or it contained life of a completely alien type. You may think that this meant it was time to launch Vikings 3, 4 and so on to investigate further but NASA abandoned landing on Mars for over twenty years (a decision forced on it not by choice but by economic necessity alas). By the mid-1990s. the Americans were planning a return to Mars, but suddenly life on Mars seemed to have been discovered not by a probe on the Martian surface but in an unlikely corner of our own planet. (To be continued…)