The Truth about Life on Mars (part 2)

Scientists had seriously considered the possibility of plant or even animal life on the surface of Mars for more than a century. However negative results from NASA�??s Viking spacecraft in the 1970s ruled out large-scale Martian life but this was not the end of the search for life on Mars.

"Welcome to the desert of the real." A bleak Martian Panorama from a Viking spacecraft (Image credit: NASA)

In the last part of this article we saw Mars had once been regarded as a home for life. Yet space missions had revealed the planet�??s surface to be utterly hostile, apart from the savage cold, the air was much, much thinner than had been thought (in fact it was virtually non-existent), the terrain was scoured by both harsh ultraviolet (UV) radiation from the Sun and cosmic rays. Any astronaut who leapt outside their Mars lander without putting their spacesuit on first would last about as long as a drummer with Spinal Tap. The hapless human would choke in the thin poisonous carbon dioxide atmosphere until he passed out. Death would follow inside a couple of minutes ҚThe dead body would freeze rapidly Қin the deep cold while the intense UV radiation would then blacken the corpse, which would quickly dry out and shrink Қas its moisture was leeched out. The gruesome remains�?? wizened features would resemble those of an Egyptian mummy or possibly those of Victoria Beckham.

No subsequent NASA Mars probe or rover since has carried any instruments to directly locate Martian life, being focussed on the planet�??s climate and geology. Over the decades, disillusionment over the possibilities of Martian life settled firmly over most of the scientific community. No seriously expected to find life on Mars anymore (but on the other hand the rocks are absolutely fascinating!) This may seem odd: surely all these Pathfinders, Sojourners, rovers and so on are meant to look for signs of life? Well NASA is painfully aware since the Apollo years that the public are not interested in rocks and as a publicly funded body NASA relies on their support. The public (or at least some of them) are very interested in aliens.Қ If the price of getting a M��ssbauer spectrometer to Mars is playing up the possibility the possibility that the mission might find an organism, well it�??s a price worth paying. In its news releases the space agency tends to play up the idea of each mission�??s purpose being to find life but (in my opinion) this is not a serious goal.

By the mid-1990s. the Americans were planning a return to Mars with a series of new space missions, 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. Let�??s have a flashback.

Once upon a time there was a little Martian rock quietly sitting on just under the Vallis Marinaris. One day, fifteen million years ago a giant meteor impacted nearby throwing thousands of tonnes of the terrain skywards. Most of this debris fell back down, but some fragments, including our rock escaped their parent world�??s gravity altogether, and fell into orbits around the Sun. Millions of years passed until one day in about 13000 BC our rock felt strangely drawn towards a warm blue planet mottled with cloud. After a hot and scary ride through a dense oxygenated atmosphere the rock crunched onto a frigid and desolate plain. Perhaps it thought it was back home again…

A visitor from a small planet (Image credit: NASA)

In 1984, meteorite hunter, Roberta Score found an interesting specimen near the Allan Hills in Antarctica. She designated it ALH 84001, a name which became famous world-wide in 1996. NASA researchers led by Dr David Mckay claimed to have discovered actual Martian lifeforms in ALH 84001!

When ancient, apparently dead, alien organisms are found frozen in the Antarctic ice, the usual protocol is to take them imbedded in a block of ice to a nearby isolated and claustrophobic research base. Then all you have to do is wait for the aliens to thaw out (they will make occasional slight but ominous movements as the ice melts away but no one will notice until it�??s too late) and eventually they will grow slimy pseudopods and start eating or taking over the scientists one by one (see Further Reading).

McKay and his colleagues chose a more careful approach. After its discovery ALH 84001 lay in storage for eight years. On examination it was realized to very unusual and was briefly thought to be a fragment of the asteroid Vesta, however by 1993 it was recognized to have originated on Mars (it has been estimated that about a billion tons of Martian rock have landed on Earth since the Solar System formed!)McKay and his team analysed the meteorite and discovered several interesting things in it, namely

1.ҚҚҚҚ Patches of carbonated minerals, suggesting that ALH 84001 had once been immersed in warm water

2.ҚҚҚҚ Chemical compounds called polycyclic aromatic hydrocarbons, usually a by-product of living organisms

3.ҚҚҚҚ Grains of magnetite crystals, commonly formed by bacteria on Earth

4.ҚҚҚҚ Tiny worm-like structures reminiscent of bacteria, there were possible non-biological explanations for 2 and 3, but this seemed conclusive evident of life from Mars.

It was item 4 that caught the world�??s attention; it seemed NASA was saying we actually had in our hands fossilised Martian lifeforms. President Clinton even announced the discovery on live television. Extraterrestrial life exists QED!

A Martian at last? (Image credit: NASA)

Sadly, there is long tradition of respectable scientists throwing caution to the wind and announcing amazing discoveries which eventually turn out not to be so clear cut. One recalls N-rays, polywater, Nessiteras rhombopteryx and, above all,cold fusion. Was this another example? Microbiologists were quick to say so, pointing out that the alleged bacteria were too tiny to be viable. A small earthly bacterium would be a sphere 600 nanometres (nm) across, meaning that you could line up 5000 of them along this capital �??I�??, yet the putative Martians were tubes just 380nm long. Contrary to popular opinion, bacteria are not �??simple�??, and are in fact packed with the machinery required for life, and most microbiologists said organisms as small as MacKay�??s �??fossils�?? could not exist. Some more sympathetic scientists made the counter claim that the Martians were genuine fossils and were examples of �??nanobacteria�?? (from the Greek �??nano�?? meaning �??itsy-bitsy�?? and from the English �??bacteria�?? meaning bacteria). These were recently discovered terrestrial organisms of startlingly small scale, but as time has passed these have been found to be oddly crystallised globs of organic molecules and inorganic minerals. Interesting, yes, but not actually alive. Nanobacteria seem to be another example of an amazing discovery which turned out to be illusory.

Today, the consensus is that the announcement of Martian life in ALH 84001 was highly premature. Inorganic processes could have created the magnetite grains, the PAH could be terrestrial contamination and the �??fossils�?? oddly crystallised minerals. There simply is not enough hard evidence to say who is correct and the debate slowly rumbles on right up to the present (finding the evidence would require a full-scale exploration of Mars by astronauts). McKay and his colleagues have continued to minutely examine ALH 84001 and other Martian meteorites. They have observed more structures which they say are of extraterrestrial biological origin, but these claims have not been accepted by the wider scientific community. A century from now I imagine McKay will be filed either with Percival Lowell or with Charles Darwin.

Martian graveyard? This is a scanning electron microscope image of a series of partly filled pits on the surface of a mineral grain from the Nakhla Martian meteorite. Similar pits are sometimes found on Earth minerals which have been attacked by organic acid generated by microbes. The pits in the Martian minerals are partly filled with debris, interpreted by some as the remains of organic microbes. (Image Credit: NASA/David McKay)

Even the most sceptical scientist would not claim that traces of Martian life (if it existed) could not be carried to Earth by meteorite. The possibility of life been carried between planets in the distant past opens up intriguing thoughts. There is excellent evidence that Mars some 3.5 billion years ago had a much denser atmosphere than it does today and that water splashed in lakes or seas on its surface. If life arose there in those distant days, could meteorite impacts have launched living cells towards our planet, making us the descendents of Martians? Alternately could life from the early Earth seeded Mars? We cannot answer these questions yet.

Meanwhile there were those, dwelling on the wilder, wackier shores of the Internet who claim that evidence of Martian vegetation, cities and monuments is staring us in the face. We�??ll examine these amazing allegations and the latest thinking on Martian life from sensible people in the third and final (I promise) part of this article.

The Truth about Life on Mars (part 2)

Scientists had seriously considered the possibility of plant or even animal life on the surface of Mars for more than a century. However negative results from NASA�??s Viking spacecraft in the 1970s ruled out large-scale Martian life but this was not the end of the search for life on Mars.

Further reading