A Home In The Sky

A tough microbe may help in
making Mars habitable, writes Biplab Das

From the pages of science fiction, the dream of colonising the red planet is inching towards real possibility. Although Mars is extremely inimical to terrestrial life, the presence of carbon dioxide and the recent discovery of subsurface water make it a likely site for human outposts. 

Terraforming Mars - altering its environment to permit human habitation - essentially involves two steps, warming the planet and changing its chemical nature. 

According to Christopher McKay of NASA's Ames Research Centre in California, the ice-capped poles of mars can be melted by reflecting sunlight on them via giant mirrors. It will also release trapped carbon dioxide. This will help because huge amounts of greenhouse gases are needed to raise the surface temperature. 

Wonder bug 

Right now, NASA cannot embark on such an ambitious project. However, what is possible is micro-terraforming. Robert Richmond, a radiation biologist of the Space Flight Centre, along with Michael Daly of Uniformed Services University of the Health Sciences and Rajagopalan Sridhar of Howard University Medical Centre stumbled upon a wonder bug called Deinococcus radiodurans. Their findings were reported in a recent issue of Proceedings, a journal published by International Society for Optical Engineering. 

This bacterium resides in many types of soil, animal faeces and sewage. Its ability to survive in any kind of extreme environment has earned it the classification of 'extremophile'. Intrigued by its tenacity, Richmond and his research colleagues scrutinised the qualities that might make it useful on Mars. 

Low atmospheric pressure and surface temperature (-60°C), accompanied by high levels of ultraviolet light and ionising radiation would freeze any terrestrial life form to death. In Daly's lab, D. radiodurans withstood extreme radiation. It also remained immune to the effects of peroxides and other oxidisers. What is more, it survived desiccation, freeze drying and exposure to solar flux ultraviolet radiation. In fact, its versatility made the group dub it a 'polyextremophile'. 

Though many extremophiles survive in the extreme environments like Antarctica and deep-sea hydrothermal vents, they cannot match the tenacity of  D. radiodurans. "What makes the research so thrilling is the chance to actually uncover the utilities of the bacterium and not just isolate it," said Richmond. 

Tougher than the rest 

The potential of this intrepid bug first came to light in November 1999. Scientists found that in the cell, its genome remains in multiple copies. This unique genetic make-up endows the bacterium with an accurate repair system. If one strand of DNA is inactivated by radiation, another strand comes to the rescue. This efficient recovery system ensures that D. radiodurans does not succumb to any extreme environment. 

Daly and his research colleagues are now working to genetically engineer the bacterium to perform that which humans cannot. "You must always think of the organism's utility in managing a habitat. You have to put the bug to work for you," said Richmond. 

Its genetic make-up might be altered so that it can detoxify Martian soil. In Daly's lab, researchers loaded the bacterium with genes that code for an enzyme, which can oxidise toluene, making the toxic compound harmless. 

Later, it is likely that it can be engineered to reduce iron or manganese ions to their elemental forms. This would push us closer to making the Martian surface more hospitable. Now, NASA's headache is to spot specific Martian sites where extremophiles can terraform small areas. 

A recent report in Science heralded the discovery of water flowing deep beneath the Martian surface. This water can be broken down to oxygen and hydrogen. Apart from breathing, oxygen in liquid form is a good rocket propellant, as is hydrogen. This underscores Mar's significance as the gateway to the outer solar system. Before this happens, Richmond's extremophiles have to chemically regulate the Martian environment, paving the way for higher forms of life. 

Why not right now? 

If micro-terraforming Mars is possible, what is stopping us from starting right away? The reason for the delay is that NASA's biologists are yet to unequivocally declare that Mars is lifeless. 

If life exists on Mars, the question arises whether we have the right to tamper with their environment. And, even if it is sterile, are we justified in exploiting its resources? 

Despite the ethical considerations, McKay is in favour of terraforming. He argues that an active biosphere on Mars would provide a refuge for humans in the event of a catastrophe that might jeopardise life on earth. Moreover, planets with life on them have a greater intrinsic value than those without. 

But one can't help recollecting the late Carl Sagan's apprehensions. In Cosmos, he wrote, "What shall we do with Mars? There are so many examples of human misuse of the Earth that even phrasing this question chills me."