Life on Mars?
ONE GENERATION AFTER THE FIRST CONTROLLED EXPERIMENT ON ALIEN LIFE: LIFE ON MARS?
Some years ago there was a furor over a picture from NASA where it appears a "face on Mars", a monumental structure which for many was an Egyptian sphinx, next to some "pentagonal pyramids." But the expectations of the scientific community have always been much more modest: they would content with finding some bacteria.
The photo in question was taken in 1976 by the Viking Orbiter 1 probe-satellite, whose cameras could show details on the ground that had a minimum size of 100 m. In 1996 NASA launched a new space probe, the Mars Global Surveyor, with cameras capable of taking pictures 10 times sharper and with a topographic laser altimeter. Conclusion: they are just natural mountains. There are no Martian civilizations.
THE IMPORTANCE OF A FOSSIL OF ONE BACTERIUM
In 1961 Frank Drake, who was looking for extraterrestrial civilizations with radio telescopes, reminded us the obvious: first, we do not know if life can arise on other planets.
Some believe that the fact that inanimate matter has suddenly become alive is so extraordinary that it must have been the result of an accident, so improbable that it only happened once (3800-million years ago) and in only one place in the Universe (here on Earth). Others go further and consider that the "accident" is not only improbable but impossible, and could only happen through the intervention of "a higher being."
Those who believe that life did emerge in other places think that, on the contrary, we are nothing special and that life must be a constant in the Universe and not an exception. The scientific basis for this theory came in 1860 when Louis Pasteur discovered that no living being can be created from nothing and that every being alive today comes from a previous one. In 1859 Charles Darwin explained that natural selection results in the evolution of living species, that is, that once upon a time living beings were much more primitive, down to simple cells. And in 1953 chemist Stanley Miller proved experimentally that, under appropriate conditions, simple chemicals come together to form complex molecular structures, such as those found in our bodies.
As far as we know, all objects fall down both on Earth and on the Moon or Alpha Centauri; all chemicals that are here also exist in the rest of the Universe, and those we detect out there are also all here on Earth. The question is: are there some "laws" of Biology that are the same anywhere in the Universe? Finding a simple alien bacterium may help answering this mystery.
THE MARTIAN ENVIRONMENT
Mars is the only planet whose surface we can see through a small telescope: a sand-colored ball (a giant desert) with white spots near the poles: polar caps that wax and wane with the seasons. It also has dark spots that for some time raised the possibility of being vegetation. In 1895 Percival Lowell even got to write that he saw straight lines emerging from the ice caps and heading toward the Martian equator: channels, he hypothesized, to supply water to a dying Martian civilization. But in 1965 the Mariner 4 space probe discovered that Mars has many craters, which means a lack of water erosion, that is, it have not rained there for billions of years, due to the very low atmospheric pressure. Hopes revived in 1971, when the probe-satellite Mariner 9 began to make global maps of Mars, where dry riverbeds appear, indicating that a more benign environment was in place just at the same time life was arising here on Earth. Why it would not also arise on Mars?
FIRST SEARCH FOR LIFE ON MARS
In the early years of the Space Age a consensus was reached that life on Mars was to be searched as soon as possible, when the planet was still kept uncontaminated by humans. In 1968 the Viking interplanetary project was approved, the most complex and expensive one up to that time: almost one thousand million dollars. These would be double space probes, where one half was orbiting the planet, studying it from above, and the other half went down to the surface.
On 20 July 1976, after detaching from the Viking Orbiter 1, Viking Lander 1 finally touched down. The first picture transmitted from Mars shows one of its legs and confirmed that it was firmly supported against the surface. On 3 September 1976 Viking Lander 2 descended on the opposite hemisphere. These spacecraft got the first meteorological and geological measurements from the surface of Mars itself.
Unable to return to Earth, they had several instruments to detect life remotely. First and most obviously, a pair of cameras. They found no horses or Martian trees, so it was assumed that there was no macroscopic life. So the next thing to do was to find microscopic life, which on Earth is found everywhere and withstands all types of weather. Many samples were collected with robot arms and were placed in various instruments within each spacecraft. One was a gas chromatograph coupled to a mass spectrometer, to detect any type of molecules that are usually present in living organisms. Another device had separate chambers where various samples could be subjected to basically three experiments: one to detect chemical reactions that would indicate breathing-like metabolic processes, one for chemical reactions that would indicate digestion-like processes and another for signs of photosynthesis.
The three metabolism experiments gave the following result: positive. But (there is always a but) the fourth experiment did not: the gas chromatograph and mass spectrometer could not detect any molecules associated with living things. This equipment had been tested in the dry deserts of Antarctica, and even in these inhospitable places it had been able to detect complex organic molecules, but not on Mars. In other words, there was metabolism but the body was not, nor even its blown-by-the-wind remains. Both spacecraft, in opposite hemispheres, gave similar results.
Today, 35 years later, we can make the following reflections: either the chemical reactions were not of biological origin, that is, were generated by substances of the soil itself, as peroxides or superoxides. Or some kind of biology, with another class of molecules for which the instrument was not prepared, was detected, for example, life forms made from molecules that do not contain carbon. Or both spacecraft suffered very similar technical failures. Or simply Mars is more inhospitable than the most inhospitable place on Earth, Antarctica.
THE MARTIAN METEORITE
Meteorites are rocks that fall from the sky. Of those found so far it was discovered, by comparison with analysis made by spacecraft, that about 40 correspond to the Moon, and another thirty, to Mars, probably thrown into space by collisions with asteroids. One that was part of Mars more than one-thousand-million years ago was at the center of a controversy when, in 1996, David McKay and colleagues presented a scientific report entitled "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001." They showed that it is a volcanic rock that had been exposed to a fluid medium, that it has carbonate globules, magnetite particles and iron sulfate (residues that are common in certain types of metabolic activity) and complex organic molecules and what look like microfossils of bacteria. The confusion came because some wanted to use the word "possible" as meaning "probable", and some people went as far as understanding it as "proven". It is possible that bacteria have existed on Mars and then were launched toward the Earth, but it is thought that it is very unlikely that what was found in that meteorite in particular are evidence of extraterrestrial life. Reflecting on the case 15 years later, we still have the following doubts: or the meteorite contained Martian life; or it was contaminated later, on Earth; or the "clues" are all non-biological, natural mineral processes. Once again, the principle developed by David Hume, Pierre-Simon Laplace, Marcello Truzzi ("On the extraordinary: an attemp at clarification", Zetetic Scholar, Volume 1, Number 1, 1978, pp. 11-19) and others and popularized by a certain person applies: you would better have some pretty extraordinary evidence if your are going to take seriously some quite extraordinary claims, so you could prove them.
NEW POSSIBILITIES OF FINDING LIFE ON MARS
In 2000 the Mars Global Surveyor photographed, with a 2-m resolution, what appear to be marks or gullies carved by water springing on the desert: as the sands are always changing, we are not talking about water in the distant past, but in our present time. Although apparently in this case they are the result of thawing, it is possible that water do exists protected in underground sites. New spacecraft are investigating this possibility.
In 2004 the European Space Agency tried to land the Beagle 2 space probe, which had a mass spectrometer 10 times more sensitive than those of the Vikings, seeking to detect the hypothetical molecular residues of Martian life. Unfortunately the mission was lost.
NASA continues its policy of sending space probes to Mars every 26 months. All spacecraft that will land must be completely sterilized to avoid spoiling future biological experiments, and to avoid destroying any form of Martian life. Missions are already being considered that would place, at last, a rocket capable of launching from Mars to Earth capsules with fresh samples, for more detailed and reliable analysis in laboratories based back here. Of course, always avoiding contaminating our planet with any life form from Mars.
Anyway, finding extraterrestrial life is more important than any human colony anywhere in the Universe. Mars is a Petri dish that must not be touched except by highly sterilized robotic probes, for a time advised by astrobiologists. This goes for NASA, Russia, China and private enterprises. If we think dispassionedly, there is no rush to send humans to Mars. As a friend of mine used to say, we should advance slowly but with good handwriting.
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Based on a lecture given at the USP, on 30 August 2003. Originally published in ABC Color, on 10 September 2006. Photo: The Viking Lander 2 covered by Mars dust blown by the strong winds. At center, the mast of the parabolic antenna for communication with Earth. At right, one of the nuclear generators. Bottom right, part of the round mouth of the biological processor. Credit: NASA / JPL-Caltech. With permission from NASA HQ History Program Office.