Antarctic ice (Holmes, 1996: 4). In reply it was argued that this was unlikely as the meteorite handling facility at the Johnson Space Center has been dealing with meteorite samples for thirty years and has developed very tight procedures to minimize possible contamination (Jakosky, 1998: 146). It was also unlikely to have been contaminated during the 13,000 years it rested in the Antarctic ice. Other meteors have been collected from the Antarctic and tested in the same way as ALH84001 with no evidence of contamination.

There were disputes over the age of the fossils and doubts were expressed whether bacteria of the alleged size could actually contain genetic material. Moreover, no evidence of cellular structures had been detected in the fossils prior to the announcement (see Kiernan et al., 1996: 4–5). One sceptic, Dr Monica Grady, Curator of Meteorites at the Natural  History  Museum, London, who has examined chunks of ALH84001, told the Observer (11 August 1996: 20): ‘I am completely unconvinced there is any evidence on this meteorite to support the idea that life once existed on Mars.’ Sceptics argued that  the  evidence presented did not conclusively rule out the thesis that what had been observed in the meteorite could be explained with reference to inorganic processes. Other sceptics have argued that the temperature in which the alleged microfossils were formed was probably too hot for any micro-organism to survive. The sceptics maintained that the tiny egg-shaped structures were too small to represent living forms, although claims have been made that some forms of terrestrial bacteria are almost as small.

One intriguing feature is that while the Martian samples are smaller than any known bacteria, their overall shape is similar and very unlike non-biological structures. A further hint that living forms the size of the Martian fossils exist comes from Western Australia, where the geologist, Philippa Unwin, and her colleagues claim to have detected living forms in sandstone deep  beneath the seabed in Western Australia. These candidates are called ‘nanobes’ and measure between 20 to 150 nanometres in diameter. Although their credentials as living organs have not been determined, if nanobes are living structures they would add support to the claim that the Martian meteorite actually contains fossilized bacteria, as some of those fossils were merely 20  nanometres across (Dayton, 1999: 13).

So far the evidence is not strong enough to rule out either the claims  of  biological structures or non-biological structures. However, claims in favour of the existence of primitive life continued throughout 1996. In November British scientists from the Open University and the Natural History Museum an-nounced that they had discovered further signs of microbal life in the Martian meteorite, 79001, that was formed 180 million years ago.

An outright dismissal of the hypothesis that there is or was life on Mars may be premature. Questions still remain open about life in the distant past, which could be resolved affirmatively by the discovery of fossils in the great ice cliffs. The debate will not be conclusively settled until a widespread search has been conducted, which will include samples taken from beneath the Martian surface.

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Now that the search for life on Mars has been regenerated, a series of NASA spaceflights have been proposed. In November  1996 the Mars Global Surveyor set out to bring back samples of the Martian surface in the year 2005. In September 1997, Global Surveyor began its orbit of Mars. This project reveals assumptions concerning the probability of Martian life, as samples of  the  rock will be subject to quarantine, according to NASA regulations, and will continue to be so when the space probe returns in the year 2005. Quarantine will, however, add many millions of dollars to the cost of missions (Kiernan, 1997: 6). Nevertheless, Global Surveyor is expected to generate as much data as all previous Mars missions combined. Since March 1998, it has been obtaining photographs with a resolution of a few metres and searching for potential future landing sites, such as ancient lake beds which may also be useful places to search for signs of former life. Despite the ill-fated Mars Polar Lander in December 1999, further missions are planned. The European Space Agency intends to launch the Mars Express Orbiter mission in 2003, with a British lander, Beagle 2, which will obtain soil samples, and further missions are planned for 2005 and 2007, which will obtain soil samples and deploy robots.

These surveys will look for evidence of life, and evidence of conditions which could have supported life. Geological evidence  suggests that ancient Mars – about three and a half billion years ago – once enjoyed a warmer, wetter climate, with liquid water at or near the surface. There is evidence of water erosion in networks of valleys and flood channels, hot springs associated with volcanic activity, and erosion of the sides of impact craters. However, high resolution images from the Mars Global Surveyor in 1999 have suggested that what have appeared to be dried-up river beds are more likely to be channels caused by an upsurge of water from within the planet in a one-off flood. These data are incompatible with theories which are suggestive of rivers fed by  rainfall and a climate roughly similar to Earth. Rivers fed by rainfall have a distinctive pattern of tributaries, and over long periods of time the course of a river may change. But this does not seem to be observable on Mars, which suggests that apart from one massive flooding,  Mars has been dry throughout its history. If this is the case then theories regarding the former  existence  of complex living systems will be weakened. But evidence could be sought of former hot volcanic springs which could have supported primitive forms of bacteria. If there were hot springs, then a search in their vicinity would be an ideal place. Images from the Mars Pathfinder project in 1997 are indicative of a former water-rich environment in the Aires Vallis region. Sand dunes and possible water-worn rock conglomerates suggest that water once flowed through this valley. In the next few years the planned missions may well incorporate a search for signs of life that the Viking missions may have missed (Jakosky, 1996: 39–42).

The more exotic contemporary claims regarding life on Mars centre on interpretations of a number of anomalies in a region of Mars known as Cydonia. One of the Viking photographs (frame 35A72) taken from an altitude

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