The planet Mars, the celestial symbol of war and strife, shines a dull red color in our earthly sky; it is truly different in appearance from the other planets, which shine with a resplendent silvery glow. Indeed, this malevolent orb, which casts its one-eyed Voldamor-tian1 gaze upon us, can affect our bodily humors, or so the astrologers of yesteryear would tell us, and it can determine the outcome of conflict and dastardly enterprise. None of us really believes in such astral influences anymore, but we do know that if Mars isn't a deathly world, it is an apparently dead and decidedly barren one (Figure 3.2).
Both Colgrove and Johnson, the authors of the treasures we found in secondhand bookstores, argue that Mars is habitable, although Johnson, writing in 1955, scales back the claim by stating that only plant life can flourish there. That even plant life is not possible on the surface of Mars was not revealed to us until July of 1965 when the Mariner 4 spacecraft dashed past the Red Planet to reveal a barren and cratered world. Indeed, the conditions that currently prevail on Mars (discussed in more detail in Chapter 6) clearly preclude the existence of anything other than bacterial life
living there now. Just as with Venus, so our understanding of Mars has changed dramatically during the past 50 years.
Although our hopes of finding distinctive indigenous life on the surfaces of Mars or Venus have been reduced to near zero over the past half-century, Mars may yet come back to surprise us. The mighty Martian microbe is currently a much-sought-after beast, and as this chapter was being written, the NASA Phoenix Lander mission (Figure 3.3) was successfully launched, and is on its way to
An artist's impression of the Phoenix Lander on Mars. Image NASA.
Figure 3.3. courtesy of
An artist's impression of the Phoenix Lander on Mars. Image NASA.
look for microbial life in the periodically watered soils close to Mars' northern polar cap. Many researchers expect that microbial life will be found on, or as is more likely, below the surface of Mars, and should this expectation be confirmed, then the hope of finding indigenous life elsewhere in the Solar System is greatly improved. More than this, however, if life has managed to survive on Mars, then it is already a habitable planet (at some level), and from the terraforming perspective, this is a great head start. Rather than starting from scratch, one can hope to build upon what already exists and thrives. Genetically engineered indigenous Martian microbial life might just be the tool needed to help transform the planet into a state that can support future human colonies.
The Phoenix Lander mission, and the variously planned follow-up surface exploration and sample-return missions, may confirm the existence of present-day Martian microbial life (time will tell, while we wait with baited breath). In the meantime, however, before the in situ results are gathered in, there are a number of observations that hint at the possibility that life did exist on Mars as recently as perhaps a few hundred million years ago. Even more incredibly, the evidence for this possibility is held inside the interiors of rock fragments that were blasted from the surface of Mars and that now reside on the Earth as meteorites.
One of the more recent invasion attempts by Mars began on 28 June 1911. Out of the clear, azure blue skies above El Nakhla El Baharia, Egypt, a rain of blackened stones pelted into the Sun-baked ground. It was 9:00 a.m. local time. The first warnings that something tremendous had happened were the rising sounds of thunderous booms that rolled and thudded across the landscape. Their attention caught, local observers glanced heavenward, and their eyes beheld a long, braided cloud of smoke that writhed in the sky, slowly twisting and turning like some tormented snake.
Rumors soon started to spread. Strange stones had apparently fallen after the strange celestial sounds had passed. Within a few days, some 40 rocks, weighing in at a total mass of about 10 kg, had been collected. It was claimed that one of the stones had struck and killed a dog, but there is no real evidence for this having actually happened. The Nakhla meteorite—as the fall of stones is now collectively known—was soon recognized as being oddly different from other meteorites, although its Martian origins2 were not to be discovered until many years later.
Time slides forward 73 years. Moving from the scorching desert heat of Egypt, our gaze shifts to the frigid ice-covered desert of Antarctica—a world away from Nakhla. A bundled-up, parka-clad field researcher working in the Allan Hills area east of the McMurdo Research Station stoops to pick up a rock. Lying exposed on the wind-blown surface ice, it is clear that there is something odd about the find, which is obviously a meteorite. Stored and carefully cataloged, the frozen meteorite is eventually given the less than inspiring name ALH84001. The first three letters identify the collection site (Allan Hills), the 84 indicates the year in which it was found (1984), and the 001 indicates that it was the first meteorite studied from the 1984 Antarctica collecting season. ALH84001 turned out to be another Martian meteorite.
There are currently 36 recognized Martian meteorites,3 but Nakhla and ALH84001 are extra special—according to some researchers—in that they betray evidence for interior alteration due to microbes, Martian microbes, that is. The hubbub began in August of 1996, when David McKay (NASA, Johnson Space Center) and co-workers published a remarkable paper in the prestigious
research journal Science. Their claim was Earth shattering in potential; they had found evidence for the existence of Martian bacteria in ALH84001 (see Figure 3.4).
The McKay et al. research paper caused a worldwide buzz of interest. Here, for so it was claimed, was a whole series of observations, admittedly none of which was entirely conclusive, but when all viewed together were highly suggestive that life had both emerged and thrived on the Mars in the distant past.4 Subsequent studies by many hundreds of researchers have certainly weakened the initial claims outlined by McKay's group, and although it is no longer clear that ALH84001 presents any direct or unambiguous evidence for the existence of past life on the Mars, there are still many researchers who feel that the ALH84001 data hasn't been totally explained or annulled. The research continues.
While work on ALH84001 carries on in laboratories around the world, McKay and co-workers have more recently suggested, at the 2006 Lunar and Planetary Science meeting in Houston, Texas, that signs of indigenous biotic alteration can be seen in the Nakhla meteorite (Figure 3.5). Specifically, a carbon-rich substance has been found to permeate some of the small cracks observed within a small sample of the meteorite. This material, McKay and co-workers note, is similar to that deposited by microbes in volcanic glass found in the Earth's oceans.
It is probably fair to say that the jury is still out with respect to the detection of in situ microbe alteration of Martian meteorite material. There are hints at possible microbial alteration, but
many alternate hypotheses can be formulated. This is the very stuff that great scientific debates are made of. The ultimate test for the presence of past (even current) life on Mars, however, will have to wait for a few decades, yet while we await (with ever-growing anticipation) for material samples collected in situ on Mars to be returned to the Earth.
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