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Although separated by tens of millions of miles of empty space, Mars and Earth participate in a mysterious communion.
Repeated exchanges of materials have taken place between the two planets, the most recent involving spacecraft from Earth that have landed on Mars. Likewise we now know that chunks of rock thrown off from the surface of Mars periodically crash into Earth. By 1997 a dozen meteorites had been firmly identified as having originated on Mars. They are known technically as SNC meteorites (after Shergotty, Nakhla, and Chassingy, the names given to the first three such meteorites found) and researchers around the world are on the lookout for more.
According to calculations by Dr. Colin Pillinger of the U.K. Planetary Sciences Research Institute, 100 tons of Martian material arrives on Earth each year.
One of the Mars meteorites, ALH84001, was found in Antarctica in 1984. It contains tiny tubular structures that NASA scientists sensationally identified in August 1996 as possible microscopic fossils of bacteria-like organisms that may have lived on Mars more than 3.6 billion years ago.
In October 1996 scientists at Britains Open University announced that a second Martian meteorite, EETA 79001, had also been found to contain the chemical signatures of life -- in this case, astonishingly, organisms that could have existed on Mars as recently as 600,000 years ago.
Two probes were launched by NASA in 1996 Pathfinder, a lander-rover, and Mars Global Surveyor, an orbiter. Further missions are budgeted to follow through 2005, when an attempt will be made to scoop up a chunk of the surface rock or soil of Mars and then return the sample to Earth. Russia and Japan are also sending probes to Mars to undertake a range of scientific tests and experiments.
Longer term are plans to terraform the Red Planet. This would involve the introduction of greenhouse gases and simple bacteria from Earth. Over a period of centuries the warming effects of the gases and the metabolic processes of the bacteria would transform the Martian atmosphere, making it habitable by more and more complex species, either introduced or locally evolved.
How likely is it that humanity will be able to fulfill this plan to seed Mars with life?
Apparently it is only a matter of finding the money. The technology to do the job already exists. Ironically, however, the existence of life on Earth itself remains one of the great unsolved mysteries of science. Nobody knows when, why, or how it began here. It just seems to have exploded suddenly, out of nowhere, at a very early stage in the planets history. Although Earth is thought to have formed 4.5 billion years ago, the most ancient surviving rocks are younger than that about 4 billion years old. Traces of microscopic organisms have been found going back almost 3.9 billion years.
The transformation of inanimate matter into life is a miracle that has never repeated itself, one that even the most advanced scientific laboratories cannot replicate. Are we really to believe that such an amazing piece of cosmic alchemy could have occurred by chance in just the first few hundred million years of Earth's long existence?
Professor Fred Hoyle of Cambridge University does not think so. His explanation for the origin of life on Earth so soon after the formation of the planet is that it was imported from outside the solar system on great interstellar comets. Some fragments collided with Earth, releasing spores that had been held in suspended animation in the cometary ice. The spores spread out and took root all around the newly formed planet, which was soon densely colonized by hardy microorganisms. These slowly evolved and diversified, eventually producing the immense range of life-forms that we know today.
An alternative and more radical theory, supported by a number of scientists, is that Earth could have been deliberately terraformed 3.9 billion years ago, just as we are now preparing to terraform Mars. This theory presupposes the existence of an advanced star-faring civilization or more likely, many such civilizations distributed throughout the universe.
Most scientists do not see the need for comets or aliens. Their theory, the mainstream view, is that life arose on Earth accidentally, without any outside interference. They further argue, on the basis of widely agreed calculations about the size and composition of the universe, that there are probably hundreds of millions of Earth-like planets spread randomly across billions of light years of interstellar space. They point out that it is improbable, amid such legions of suitable planets, that life would have evolved only on Earth.
WHY NOT MARS?
In our own solar system, the first planet out from the Sun, tiny, seething Mercury, is believed to be incongenial to any imaginable form of life. So too is Venus, the second planet from the Sun, where concentrated sulphuric acid pours down twenty-four hours a day from poisonous clouds. Earth is the third planet from the Sun. The fourth, Mars, is indisputably the most Earth-like in the solar system. Its axis is tilted at an angle of 24.935 degrees in relation to the plane of its orbit around the Sun (Earths axis is tilted 23.5 degrees). It makes a complete rotation around its axis in 24 hours, 39 minutes, 36 seconds (Earth's rotational period is 23 hours, 56 minutes, 5 seconds). Like Earth, Mars is subject to the cyclic axial wobble that astronomers call precession. Like Earth it is not a perfect sphere but somewhat flattened at the poles and expanded into a bulge at the equator. Like Earth it has four seasons. Like Earth it has icy polar caps, mountains, deserts, and dust storms. And although Mars today is a freezing hell, there is evidence that in some ancient period it was alive with oceans and rivers and enjoyed a climate and atmosphere quite similar to those of Earth.
How probable is it that the spark that ignited life on Earth would not also have made its mark on neighboring, similar Mars? Whether Earth was deliberately terraformed, in other words, or whether it was seeded with the spores of life from crashed cometsor whether, indeed, life arose here spontaneously and accidentallyit is reasonable to hope that we might find traces of the same kind of process on Mars.
If such traces are not forthcoming, then the chances that we are alone in the universe increase and the chances of life being discovered anywhere else are dramatically reduced. The implication will be that Earth's life-forms emerged under conditions so focused, specialized, and unique and at the same time so random that they could not be replicated even on a nearby world belonging to the same solar family. How much less likely, therefore, that they could be replicated on alien worlds in orbit around distant stars.
For this reason the question of life on Mars must be regarded as one of the great philosophical mysteries of our time. With the rapid advances in exploration of the planet it is a mystery that is soon likely to be solved.
HINTS OF LIFE
The evidence in from Mars so far takes four principal forms:
1. Earth-based observations from telescopes
2. Observations and photographs from orbiting spacecraft
3. Chemical and radiological tests carried out on Martian soil samples by NASA landers, with the results being transmitted back to Earth for analysis
4. Microscopic examination of meteorites known to have come from Mars
In the late nineteenth and early twentieth centuries, Earth-based telescopes produced the first ever life on Mars sensation -- the claim that the planet was checkered with a gigantic network of irrigation canals bringing water from the poles to the parched equatorial regions. This claim, which we shall discuss further in part 2 of this book, was put forward by Percival Lowell, a prominent U.S. astronomer, and made an indelible mark on the collective psyche of Americans. Most scientists ridiculed Lowell's ideas, however, and in the 1970s, NASA's Mariner 9 and Viking 1 and 2 probes orbited the planet and sent back definitive photographs proving that there were no canals.
It is now recognized that Lowell (and others who claimed to have seen the canals) were the victims of poor-quality telescopic images and an optical illusion that causes the brain to link disparate, unconnected features into straight lines. Even today, no Earth-based telescope has sufficient resolution to allow us to solve the mystery of life on Mars. We must therefore make our deductions using the three other types of evidence available to us: Martian meteorites, orbiter observations, lander observations.
We have already seen that two of the Martian meteorites appear to contain traces of primitive microorganisms (although many scientists disagree with this interpretation). Less well known is the fact that a number of the tests carried out in 1976 by the Viking landers also proved positive for life.
Posted December 13, 2007
This book shows some compelling scientific evidence about why Mars looks the way it does and some anomalies that Mars gives us. Such mysteries are so thrilling and enjoyable to read!
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