Mars has always fascinated humankind. Its baleful colour and striking hundred-fold variation in brightness, from second only to Venus to dimmer than amma Crucis, the star at the head of the Southern Cross, make it remarkable amongst the planets. Also, as the Earth swings past it on the inside track, for a while Mars appears to reverse its movement against the stellar background.
In 1666, Cassini established that the length of the Martian day was only 40 minutes longer than that of the Earth. This was a powerful inducement to believe that the planet would prove to be similar in other respects and therefore support life.
A century later, the “Mars is a little Earth” school received an enormous boost when William Herschel, using his excellent reflecting telescopes, discovered the polar caps and their seasonal variations which march with colour variations elsewhere on the planet. He also determined that the obliquity of the Martian ecliptic is within a tad of that of the Earth, 23°44′, and to cap it all, observed evidence for an atmosphere. Only the fact that Mars was smaller than the Earth prevented it from being an identical twin.
In 1877, when Mars was at opposition and only 56 x 11:30 kin from us, Schiaparelli discerned a number of fine, straight markings on the surface. In his report he called these cattail, or channels, but only too easily the translation became “canals,” and as such the first evidence of alien constructions on this most likely home for alternative life forms. At the same time, Asaph Hall discovered the two moons of Mars, which had apparently been foreseen by Jonathan Swift in his Gulliver’s Travels.
Although many astronomers failed to confirm Schiaparelli’s observations, the wealthy and gifted amateur astronomer Percival Lowell was not among them. Fired with a belief in Martian life, he built the observatory at Flagstaff, Arizona, for the express purpose of observing Mars. With a 24-inch refractor, the biggest of its time, he made thousands of observations and a multitude of drawings and photographs. With these data he constructed maps and globes of the planet showing more than 200 “canals,” many paired and all so straight as to argue that they must be artificial constructions. From here it was but a step to his picture of an intelligent race trapped on a slowly desiccating planet, bending their efforts to channel the remaining water from the melt of the polar caps to their cities.
If the public needed anything further to fix its attention on Mars, The War Of The Worlds by H. G. Wells was to supply some of the most memorable bug-eyed monsters ever to challenge the assumption of human superiority. These Martians were the antithesis of Lowell’s pacific, globally co-operative race struggling for survival, for Wells’ creatures, faced with the same threat, used their technological superiority for conquest.
In spite of the commissioning of the 100-inch Hooker Telescope on Mount Wilson during World War I and of the 200-inch Hale on Mount Palomar after World War II, Mars could not be seen well enough through our atmosphere to settle the question of it supporting life.
By then, only the most dedicated Lowellites continued to “see” canals, and spectroscopic analysis painted a picture of a dry, frozen and almost airless planet. But Mars continued to fascinate, and inspired in Ray Bradbury’s Martian Chronicles some of the best science fiction short stories ever published.
The first clear look at Mars came with the fly-by of Mariner 4 on July 14 1964. Mariner photographed only one per cent of the planet’s surface, but this was enough to consign Lowell’s canals to the archives of optical illusion, for what was revealed was a sterile, cratered surface, apparently similar to that of the Moon.
Five years later, Mariners 6 & 7 made low-altitude flybys and confirmed that Mars was barren. Then, in November 1971, Mariner 9 went into orbit around the planet and photographed the entire surface. We saw not just craters, but for the first time great volcanoes, chasms far larger than any on Earth and, most surprisingly and significantly of all, sinuous channels which had every appearance of being wadi: dry river beds. If indeed this is what they are, and no reasonable alternative has been proposed, then Mars must once have had substantial amounts of liquid water, and so the possibility of life.
Following the Mariners came the Viking orbiter/ landers, the most complex interplanetary spacecraft yet launched. On arrival in July and August 1976, Vikings 1 & 2 went into orbit around Mars, and both released a lander unit which made a soft landing and relayed back physical data, photographs and the results of life-detection experiments. The photographs confirmed a desolate landscape of sand and rock, and the search for signs of life yielded at best equivocal results. However, the failure to confirm any evidence of life in a few grams of desert sand is not conclusive a small random sample from the Sahara or Gobi is not likely to do any better.
It was not until September 1992 that the next spacecraft, Mars Observer, lifted off on its 11-month journey to go into orbit and perform a global survey of the surface and atmosphere. The six instruments it carried were to map the whole planet topographically, geologically and meteorologically, but, at the last moment, probably while making an automated braking manoeuvre, contact with the craft was lost and never regained.
Five years later, a fleet of three space craft was launched with a range of instruments and experiments designed to make up for the loss of Mars Observer. Unhappily, the biggest and most elaborate of them, the Russian Mars 96, was lost when the upper booster failed and the space craft was destroyed over the Pacific. Of the two remaining craft, NASA’s Global Surveyor is on course and functional, and, as this issue goes to press, Pathfinder has landed and become a focus of world attention.
Pathfinder’s job was to get the remote-controlled Sojourner vehicle on to the surface, where it is being used to test command and control technologies as well as take high-resolution close-up photographs of selected objects, together with X-ray spectrographs which will reveal chemical composition.
Global Surveyor, due to arrive in September, will photograph the surface at a resolution of three metres—just fine enough to spot the Vikings—while its spectrometer and laser altimeter will carry out the meteorological and topographical mapping originally intended for the ill-fated Mars Observer.
Both spacecraft have been designed, built and programmed under rigid financial constraints, and this has meant abandoning elaborate, fuel-expensive braking manoeuvres. For Global Surveyor, this means being slowed down by a single 20-minute burn from its engine, to place it in a highly elliptical orbit, and then its specially strengthened solar panels will act as air brakes. As the craft dips into the upper levels of the Martian atmosphere, each successive skim past the planet will slightly slow it. One hundred and thirty days of this deceleration will bring the craft into the required circular polar orbit.
Pathfinder approached Mars without any preliminary braking manoeuvres, crashing through the atmosphere on July 4 behind a Viking-type heat shield, and then deployed parachutes and airbags on which the lander bounced to a stop. Three “petals” shrouding the lander opened to allow Sojouner, the 11.5 kg microrover, out on to the surface for a few weeks of exploration—at a speed not exceeding a sedate 40 cm per minute (see map below).
If Global Surveyor and Pathfinder/Sojourner perform as intended, they should pave the way for later instruments which may settle once and for all the question of whether life exists or has existed on Mars.
To some, meteorite ALH 84001, the Antarctic rock which caused such a stir last summer, has already answered this question in the affirmative, but others doubt the reality of “bacteria” only 0.01 times the size of their terrestrial counterparts. For others, the so-called “Face on Mars” is evidence of not only life but civilisations past. The “face” is no more than a trick of the light, and as the direction of the sun or the angle of view changes, so the face disappears. (A number of such phenomena are known on Earth, including-the Duke’s Head in Whangaroa Harbour.)
The questions of life, its origins, its varieties, its chemical construction and processes, cut to the bone and always engage us. Is there life elsewhere? How common is it within our section of the galaxy? Is there only one basic sort? Do the strange fossil forms preserved in the Burgess Shales represent inherently faulty organisms, or were they extinguished through some outside agency such as a massive asteroid impact, so that elsewhere they became the precursors of forms unimaginable? Are there other intelligences?
There are cogent arguments supporting the claim that only a C, N, H, 0 and liquid water-based system can support life—that only this combination can provide the stability and energy transfers for the huge molecules which are essential to life processes. But this is not to say that all life chemistries must be identical. All earthly DNA employs the four-letter code of adenine, cytosine, guanine and thymine. Are these the only possibilities, or has some analogue of “our” DNA evolved using different bases?
All being well, the results of these current missions will be encouraging enough to justify an international mission in the next 10 years to return samples of Martian soil to Earth. Fossil remains of bacterial colonies on the surface, even if hundreds of millions of years old, will lend support to the idea that there may yet be subterranean life where there is liquid water and compounds to metabolise. Such habitats would be analogous to the “black smokers” along the Earth’s ocean ridges, those fountains of mineral-rich water which support communities of bacteria and complex organisms. But it may be that Martian life could not evolve fast enough to adapt to the cooling surface and loss of atmosphere, so that only fossils remain.
But if there is or has been life on Mars which is in some way radically different from our form, then the “seeds from outer space” theory of Fred Hoyle, amongst others, appears less likely than that of spontaneous development.
On the other hand, should Martian life prove to have the same chemistry as Earth’s, this would lend support to theories which argue a common origin—but equally may merely demonstrate that there is only one life chemistry.
One thing is certain: evidence of any sort of Martian life will have as big an impact as did the publication of The Origin of Species.