6. THE FUTURE OF MARS

Future Missions

Hoping for "better, faster, cheaper" exploratory missions, NASA inaugurated its Discovery Program in 1994. The purpose was to design relatively low cost, modest projects with clearly focused goals. An educational component was built into the program in an effort to make the general public more aware of the purpose and accomplishments of its missions to Mars and to other destinations in the solar system.

In addition to Pathfinder and Mars Global Surveyor, as many as four more Mars-bound Discovery missions are scheduled through the year 2005, one launch every 26 months (1998, 2001, 2003, and 2005), at times when the relative position of Earth and Mars is most favorable. The first will be the Mars Surveyor, actually two different spacecraft--an orbiter and a lander. Their assignment will be to study weather and climate . The lander will have two small surface probes designed to look for water beneath the planet's surface, among other things.

Terraforming

Could people ever live comfortably on Mars? Today the planet is a frozen desert. Its atmosphere is too thin to allow liquid water on the surface. But the Mariner and Viking spacecraft revealed flood channels and valley networks on Mars. These features appear to be relics from a time, billions of years ago, when liquid water flowed across the surface. In that remote epoch, Mars almost certainly possessed a much denser atmosphere. The climate and environment were once more Earthlike.

Where, then, did such an atmosphere go? And where did all the water go? What caused the Martian environment to change so dramatically? Could it change back again? Are there any steps that humans might take to change it? Could Mars again become a warmer, wetter, habitable planet, more like the Earth? That is, might we be able to "terraform" Mars?

The main requirement would be to restore the dense Martian atmosphere. But where is the ancient atmosphere hiding? Although the gravity on Mars is only 38% as much as on Earth, that should have been sufficent to prevent all the atmosphere from escaping into space (as happened on the Moon). Much of the ancient Martian atmosphere and the water are apparently frozen in the Martian polar caps, which are made of dry ice (frozen carbon dioxide) and water ice. Some of it may also be hidden below the surface in the form of permafrost (ice in permanently frozen soil).

If we could somehow increase the surface temperature of the polar caps, the frozen carbon dioxide and water would begin to evaporate and increase the amount of atmosphere. Because these are both potent "greenhouse" gases, which trap heat from sunlight, they would also increase the surface temperature on Mars. That in turn would evaporate more ice, further increasing the surface pressure and temperature, in a cycle of "positive feedback". If we could sufficiently "prime the greenhouse pump", the process might even become self-sustaining and lead to a "runaway greenhouse effect".

One way to get the process started might be to "seed" the Martian polar caps with green plants or microbes genetically engineered to extract the liquid water they need from ice. These organisms would also be dark, to absorb more sunlight. They would therefore warm up the ice and increase its rate of evaporation.

The great advantage of using plants or microbes is that they are self-reproducing. Experiments have shown that some microbes can survive in a simulated Martian environment. It may therefore be possible to genetically engineer such organisms to reproduce in the environment of the Martian polar ice. Such organisms released on Mars would spread out over the ice caps in a short time.

If such a process is possible at all, it might take a few hundred years to liberate most of the remaining ancient atmosphere of Mars. The increased surface pressure and temperature would allow liquid water to condense on Mars for the first time in several billion years. There would be rain, rivers, and perhaps seas. We could then introduce other kinds of green plants to grow on Mars, obtaining their nutrients from the soil and carbon dioxide from the air, just as they do on Earth.

The following images are stills from the Imax-produced film Destiny In Space
©Smithsonian Institution/ Lockheed Martin Corporation

Once most of the ancient atmosphere of Mars is restored, the air pressure might be high enough to allow people to walk about comfortably on Mars without space suits. However, they would still need oxygen tanks and respirators (resembling scuba gear), because we can't breathe carbon dioxide. The dense new atmosphere would also shield the surface against some of the cosmic radiation from space. However, we would still need to protect skin and eyes against solar ultraviolet rays, because the atmosphere would not have any ozone layer to shield us.

The green plants would take in carbon dioxide and give off oxygen, but it would probably take thousands of years to build up enough oxygen to make a breathable atmosphere on Mars. The oxygen in turn would produce an ozone layer to shield the surface from solar ultraviolet light. We could then introduce animals, very selectively of course. Butterflies yes, mosquitoes no! The new world of Mars would be a garden.

To find out if terraforming is even possible, we will have to learn a lot more about Mars. Is there enough potential atmosphere frozen on Mars? Can it be liberated? If we find that Mars has its own life forms, we might want to leave the planet as we found it and not interfere. But if Mars turns out to be utterly barren, some of our descendants might decide to terraform it and become Martians.