Embracing a Martian future

Viewpoint

Tuesday September 11th 2007

Author Marcus Chown takes a closer look at the Mars Phoenix project, which we reported on in early August 2007 here. Chown says that he is looking forward to a time when humans can inhabit Mars

Tuesday September 11th 2007

How scientists believe Phoenix will look entering the Martian atmosphere. Image: NASA

"Mars ain't no place to raise your kids," sang Elton John in Rocket Man. And he was absolutely right. A balmy summer's day on the Red Planet is indistinguishable from mid-winter in Antarctica. But that does not mean Mars was inhospitable to life in the distant past – or that it will be inhospitable to life in the future. A new space probe launched in early August from Florida's Cape Canaveral could prove this to be the case.

Mars Phoenix is the next logical step in Nasa's "follow the water" strategy for exploring Mars. The idea is that the calling cards of life, either past or present, are most likely to be found where there are indications of water, the substance essential to life as we know it.

And where better to look than the edge of Mars’ northern polar cap, which is strongly suspected to contain large amounts of permanently frozen water? After an eight-month journey Mars Phoenix will enter the Martian atmosphere at a latitude equivalent to Alaska on Earth. It will plunge like a meteor through the thin Martian air, its descent braked by supersonic parachutes and retro-thrusters, until it comes to rest on its three spindly legs. Once its solar panels are unfurled and electricity courses through its circuits, Mars Phoenix will come to life and begin its scientific programme.

At the landing site, it will be mid-afternoon, early summer, with a weak sun in a rose-pink sky. The temperature, beneath thin high-altitude clouds, will be about -50 degrees Celsius. The lander will have come to rest in a shallow valley with no more than half a dozen metre-wide boulders strewn over the area of a football pitch and the odd impact crater. But the most striking feature of the site will be the mosaic of polygonal shapes etched into the ground. Formed as extreme winter cold causes ice-cemented soil to contract until it ruptures, such "polygonal ground" is also seen in Antarctica.

It will be into this ice-hardened crust that Mars Phoenix's robot arm will dig, striking pure ice probably within a few centimetres. The samples it retrieves will be baked in an oven on board the lander to give off "volatiles" such as water vapour. A water molecule commonly contains atoms known as hydrogen-1 and oxygen-16, but it can also contain their heavier cousins, hydrogen-2 (deuterium) and oxygen-18. Phoenix will measure the abundance ratios of the hydrogen isotopes and the oxygen isotopes.

"If the ratios do not match those in the current atmosphere, then the water cannot have come from present-day snow," says Ray Arvidson, a member of the Mars Phoenix team from the University of Arizona at Tucson. "It will be ancient water – perhaps from an ancient ocean."

Evidence is abundant that water flowed copiously on Mars during its first 500m years of history. There are sinuous channels reminiscent of terrestrial river valleys, and great gorges similar to water-cut canyons. One, the Valles Marineris, is 10 times longer and about four times as deep as the Grand Canyon. Evidence of an ancient ocean is, however, more contentious.

Mars is believed to have gone bad because, at only about half the Earth's diameter, it was unable to retain the heat of its birth for as long. It is the dynamo action of molten material circulating deep inside a planet that creates a magnetic field, which shields its atmosphere from the ravages of the million-mile an hour "solar wind". Bereft of a magnetic shield, the atmosphere of Mars was quickly stripped away so liquid water could no longer exist on its surface.

In the heated soil samples, the Mars Phoenix scientists will also be looking for evidence of "organic molecules", essential for terrestrial life along with water. These could tell them that the chemical ingredients once existed for life. Such life could either have begun but become extinct or, more excitingly, begun and lain dormant when Mars went bad. And Mars is known to undergo dramatic climate changes, warming up every 100,000 years or so.

"Water might exist briefly in liquid form and life (probably micro-organisms) might take advantage, bursting forth periodically," says Arvidson. Of course, it is always possible that the Martian soil contains desiccated bacteria, which might swim into view in images sent back to Earth from the lander's two microscopes. "We can always hope," says Arvidson.

If Mars Phoenix does find substantial quantities of water, it will be good news for future manned explorations of Mars. George Bush has called for the return of humans to the Moon by 2020, an essential first step on the long road to Mars.

Water on Mars could be used to drink, and water molecules could be split apart for oxygen to breathe and hydrogen for rocket fuel. This would avoid the prohibitive cost of carrying an estimated 20 tonnes of water from the Earth. But why go to Mars? After all, it could take six months and will be hundreds of times harder than going to the Moon. "If we find evidence of life on Mars, we are going," says Arvidson. "Simple as that."

"The real excitement will come when we send a team of humans to Mars, because then the discoveries will increase exponentially," says Kim Stanley Robinson, author of a best-selling series of science fiction novels set on Mars. "We may discover living bacteria, which would be one of the greatest scientific discoveries ever, or signs of past life in the form of fossils, or no sign of any Martian life ever, which would be interesting in its own way."

Mars Phoenix will operate for 90 Martian days as summer turns into autumn then winter and flakes of carbon dioxide snow begin to waft down, gradually burying the lander. Nobody knows whether Mars Phoenix will survive. But, if it does, when men finally do go to Mars, and Mars does become a place to raise your kids, maybe people with snow shovels will uncover it (perfectly preserved) and put it in a Martian museum. All this depends crucially on a successful landing next year.

• Marcus Chown is the author of The Never-Ending Days of Being Dead (Faber, 2007).

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