In the 70Æs the Viking Orbiter showed us pictures of a rosty, brown, deserted planet called Mars. The knowledge of it raged with dust storms and a thin athmosphere made us belive that it was lifeless and has been that way billions of years. Now scientists are seriously discussing the possibilty of life on this red planet. And the reason to that is a discovery in 1984 in the Antartic Allan Hills region. The discovery is a 1.9 kilogram meteorite that the astronomers given the anonymous name ALH84001.
By: Jorgen Westman(Picture: BSE image showing location of orthopyroxene (OPX), clinopyroxene (CPX), apatite (A), and carbonate (MgC, C). Fe-rich rims (R) separate the center of the carbonate (C) from a Mg-rich carbonate (MgC) rim)
They belive the meteorite was chipped off from Mars 15 million years ago when an asteroid or comet crashed into the planet Mars, sending small pieces hurtling into space with enough force to escape MarsÆs gravity. Some 13,000 years ago ALH84001 wandered close enough to Earth to be caught in our planets gravitational field and fell into the Antartic ice sheet. So now, after 15 million years in space and 13 000 years entombed in ice on Earth, NASA belives it shows us proof of primitive organic life on the red planet, developed in paralell with life on Earth.
ALH84001 isnÆt the first meteorite that has struck Earth. There is 11 others selected group of meteorites believed to have been blasted off the surface of Mars by meteor impacts. Collectively they are known as the SNCs, named after the three most famous examples:
Shergotty, a 4-kilogram rock which fell in India in 1865
Nakhla, a 40-kilogram boulder that fell in Egypt in 1911 (killing an unlucky dog)
Chassigny, a 4-kilogram meteorite that fell in France in 1815.
But how do we know it came from Mars and not EarthÆs other closest neighbour - Venus? Well, first of all Mars has a much more thinner atmosphere and lower gravity than Venus, making it far easier to eject meteorites. Further evidence that the 11 rocks (SNCs) were from Mars came in the 1979 when the EETA79001-meteorite fell in Antartica. Isotopic and chemical analysis of these gases matched measurements of the Martian atmosphere made by the Viking lander. The same has been found on the others.
As meteorites are lumps of metal or igneous rock that crystallised some 4.5 billion years ago, when the Solar System formed, the 11SNCs are different as they are dated between 1.3 billion and 180 million years ago. And the scientist belive that could not have come from a small body, such as an asteroid or comet, as it would have lost the heat left over from its formation quickly. The solution is - SNCs must have come from something big.
Arguments In favor of life on Mars
(Picture: TEM image of a thin section showing the morphology of the Fe-sulfide phases present in ALH84001 and a terrestrial soil sample. Iron sulfide phase (greigite?Fe3S4) is located in a magnetite-poor region separate and distinct from the magnetite-rich rims.)
The most striking thing about the Mars meteorite ALH84001 is its resemblence with earthly builded organic compounds. According to NASAÆs scientists the meteorite ALH84001 contains carbonate globules that the scientists belives was formed in the rock 3.6 billion years ago, at a time when water is believed to have flowed on the surface of Mars, probably seeping into the crust through cracks and fissures. The water would have been laden with carbon dioxide from the Martian atmosphere, producing carbonate minerals in the rock. The scientists at NASA believes the expanding carbonate globules trapped and fossilised the microorganisms. NASA researchers made four remarkable key discoveries:
1. NASA points out the markings resembling the outlines of tiny cells, iron-containing, teardrop shaped crystals similar to ones produced by some bacteria on Earth. These Earthly cells are used to navigate (compass) the bacteria around sediments. On Earth, most known bacteria are between 0╖5 to 20 micrometres long. But the Martian rods and ovoids measure between 20 and 100 nanometres. The only problem here is that Mars has only 0.2% of Earths magnetic field, so a öcompassö is useless...
2. More evidence of Earthly-like activity comes from particles of magnetite and iron sulphide found in the globules. These particles have the same shapes and composition as those produced by microorganisms on Earth.
3. The finding of more PAHs deep inside the rock than near the surface, which indicates that the PAHs (polycyclic aromatic hydrocarbons, oily molecules that are often produced as terrestrial microorganisms decay) are not a contaminant that leached into the rock during its long incarceration in the Antarctic ice.
4. The finding of magnetite and iron sulphide.
Arguments against life on Mars
(Picture: High-resolution SEM image showing ovoid and elongate features associated with ALH84001 carbonate globules. (A) Surface of Fe-rich rim area. Numerous ovoids, about 100 nm in diameter, are present (arrows). Tubular-shaped bodies are also apparent (arrows). Smaller angular grains may be the magnetite and pyrrhotite found by TEM.)
Some scientists argue that the sample might have been contaminated on Earth, as the Antartic isnÆt such a sterile place as people belive. Or that the organic componds could have mimic the signature of life on Earth.
The same scepticism can be found regarding the PAHs. PAHs are also common on other meteorites that are not thought to be from any planet, and no one thinks of them as biogenic and diagnostic of life. And the spectrum of PAHs in the Martian meteorite is a thousandfold less diverse than that found in fossils and other remains of biological material. An explanation to the smaller amount of PAHs on the surface than the bigger amount inside the meteorite is could also be that the black stone (meteorite) could absorb heat and melting snow would seep into the many fissures in the rock and concentrate PAHs on the inside. And because PAHs are destroyed by ultraviolet light, there would be little contamination of PAHs on the surface, exposed to sunlight.
A possible explanation to the carbonite isotop findings in the meteorite was presented by Ralph Harvey of the Western Reserve Case University of Cleveland and Harry McSween of the University of Tennessee. They have an alternative theory of how the carbonates was formed. They suggest that the impact of the asteroid/comet that collided with Mars created a hot fluid--hotter than 450 ║C--rich in CO2, that deposited carbonate on ALH84001 just as it was being flung into space. If it is so, there is little chance that the isoptops is proof of former organic life on AHL84001. With other words - it couldnÆt hold life.
Meenakshi Wadhwa of the Field Museum in Chicago also contradicts NASAÆs claim of the meteorite being 3.6 billion years old. From calculation of the concentration of strontium and rubidium in the meteorite, the carbonates says that it is only 1.39 billion years old, plus/minus 100 million years.
Another argument is that the bacteria on AHL84001 is too small to bare life. But this is in opposite with the findings by the microbiologist Todd Stevens,who found a bacteria, only twice the size of the Martian bacteria, beneath Columbia River in Washington. Lacking organic food and sunlight, the bacteria acquire their energy instead from chemical reactions between rock and water that produce hydrogen gas. And other microorganisms have been found in Italien hot-water springs that is dated 2 billion years old.
In AHL84001 scientists found amounts of carbon-12 and 13. Carbon-13 is heavier and less abundant the enzymes handles carbon-12 and so living organisms leaves remnants in this isotope. Some reseachers claim to have found evidence of terristrial bacteria in this isotope but no one (to my knowledge) has found the tiniest cell or any internal structure (like cell-walls) on AHL84001Æs ömicrofossilsö.
But then again - one finding that is extremely hard to explain is why Martian microorganisms produced the same teardrop-shaped crystals of the iron-containing mineral, magnetite, as earthly bacteria do. They are very large (as the Martian are small, but the same shape) and are used by the earthly bacteria to navigate around sediments. Like a miniature magnetic compass. And as I said earlier - on Mars the magnetic field (0,2% of earths) would make such ömagnetic-compass-crystalsö useless. This teardrop shaped crystal is often thought of as öthe fingerprint of biologyö due to its purpuse of navigating the bacteria.
If there was life - is it still there?
There is two types (as far as we know today) of the Martian surface. One is the old, heavily cratered, that dates back to the creation of our solar system 3.6 billion years ago. The other type is much younger and shows traces of pre-historic rivers of running water that has shaped the landscape and amazed us since 1877 when the Italian astronomer Giovanni Virginio Schiaparelli named them Canali. But erosion of the old surface has filled the smoothered out the landscape. Craters as deep as 20 kilometers are thought to be buried beneath the rosty brown soil. The surface water is belived among scientists to have both vaporized through the planets atmosphere and maybe also filtered the underground and that there is up til a 500 meter thick layer of water, in the form of permafrost, deep down in the crust. In those waters life is maybe still existing today as it could be found beneath the Colombia river.
As the Viking lander showed us a dead rocky planet we lost hope of the green little öMartiansö. Now were back to square one as NASA is launching 3 probes within the next two years, but none is design to look for life.
On November 6 NASA will launch the Mars Global Surveyo. This spacecraft is an Orbiter and is equipped with a CCD camera similar to the one on the ill-fated Mars Observor "lost" in 1993, 3 days before insertion into orbit around Mars. This is the probe that Richard C. Hoagland with others (me included) would like to see mapping the Cydonia-area.
On November 16, 1996 Russia is going to launch Mars 96 which will also reach Mars in September 1997. This spacecraft consists of an orbiter, 2 small ground stations and 2 penetrators.
On December 2 NASA will launch Mars Pathfinder which will consist of a lander and a micro-rover (1 foot long vehicle) named Sojourner.. But the Rover is not equipped to dig underground, where the possible fossils are most likely to be found. This tetrahedron-shaped craft will be landing at 19.5 degrees N latitude, 32.8 degrees W longitude.
In 1998 the US is to launch Mars Surveyor 1998, that has an orbiter and a lander. The lander has 2 small probes that will dig 2 meters into the soil. Probably not deep enough to find fossils...
Further plans of probes is to be send in 2001, 2003 and 2005. The 2001-mission is probably the earliest to be equipped to hunt for extraterrestrial lifeforms and bring them back to earth. This mission will also send a öscoutö to search for other promising spots to send later crafts.
Both Japan and Russia are planning their own Mars missions. In 1998, Japan is scheduled to send a craft to orbit Mars and study its upper atmosphere. In November this year the Russians will launch their Mars 1996 probe, that will land. And the European Sapce Agency will decide if ESA will launch a probe too, but it wonÆt see the daylight until 2007, at the earliest.
A question that raises in my head is - what if there were intelligent life on Mars earlier that progressed faster than on Earth? In that case - where is it now? Is it dead or has it escaped beneath the surface? Or has it left the planet and settled somewhere else - like earth?
Many big questions to think about. And as NASAÆs claim of life in AHL84001 is somewhat öweakö - what is their purpose to release the information at this stage? Do they sence something we donÆt - yet.
in between is exploration. -Anonymous