Is there life on Mars? The answer has eluded us for decades, and the more we explore the planet, the more elusive that answer seems to become. The discovery by the NASA rover Curiosity that Mars seems to have essentially no methane in its atmosphere is another blow to the idea that microbes flourish somewhere on this world. Then again, scientists on Earth continue to demonstrate that life can survive in Martian conditions and in even more hostile environments.

While science asks if life exists on Mars, another question lurks a few steps ahead. Would the discovery of life on Mars be good or bad for the long-term future of space exploration?

We have already had a taste of this dilemma. In 1976, two Viking landers touched down on the rocky deserts of Mars, in search of life. Soil samples were incubated in some sophisticated laboratories inside the landers.

The results were controversial, but the overwhelming opinion within the scientific community is that the Vikings failed to detect any life on Mars. The result was disappointing for science, but it seemed to be even more devastating for the exploration of the planet.

No new missions to Mars would be instigated by NASA for many years. NASA did not stage a successful return to the planet for another two decades! Admittedly, there was a whole solar system to be explored by other missions, but the neglect of the planet next to us was shocking. If life had been detected on Mars, or even if the Vikings had provided strong hints of its existence, we probably would have seen robots crawling around and performing sample return missions by the 1990s.

Discovering life on Mars will not be easy. If it exists, it is probably in a region that is difficult to reach. Some life could cling to the sides of caves or sinkholes which will be difficult for robots to explore.

A more likely scenario involves underground life. Drilling to find it would require a lot of kit and a lot of power. Right now, our understanding of underground Mars is so poor that it would be premature to even consider designing a proper mission to explore it. Getting a sample of Martian biota and testing it would be complex. The cost would be enormous. Justifying such a mission will require a lot of circumstantial evidence collected by earlier missions.

So let's assume that we discover evidence, or even a case that seems fairly plausible, that there is life on Mars. What happens next? Expect a wave of publicity and a lot of controversy. Memories of the ALH84001 Martian meteorite story in 1996 are still fresh in the minds of scientists, the media and the public.

We have also had a steady stream of dubious scientific papers in astrobiology, ranging from the alleged discovery of alien-like bacteria on Earth to claims that there are alien microbes in the upper atmosphere. As Carl Sagan preached, extraordinary claims require extraordinary proof, and the case for life on Mars will need to be rigorous. The subject will not be settled conclusively for some time. This will be a mixed blessing.

Scientific debate and discussion is usually healthy, but we hope it will not become too nasty, or risk discrediting the spaceflight and scientific communities before a skeptical public. Many ventures in science and spaceflight are already viewed with suspicion, and a chaotic response to an alleged Martian life discovery would only fuel such viewpoints. But most great concepts in science have been forged with passion and disagreements. Let the people see the fray and know that they are not being kept in the dark!

The issue of discovering life beyond Earth, whether it is in the form of microbes or little green men, would be of profound significance to society. It would cause us to evaluate our own place in the universe and the overall nature of life in the universe. This has sociological, psychological, philosophical and theological implications. Some people will respond differently to others. Some people will struggle to accept this or react in unpredictable ways. Some of them may even have influence over governments.

As the shouting fades, calls will gradually rise for sending more missions to Mars. There would be a lot of interest in finding out more about what will probably be the first aliens we encounter. Robot laboratories will be designed. The testing will be more rigorous, the data more substantial. There will also be calls to cease and desist from all Martian exploration!

Some practical arguments for treading softly with even our current fleet of robot probes can be made. Discovering life on Mars would suggest that the planet could be an oasis in the solar system, isolated from the teeming millions of different species on Earth. Sending spacecraft there risks invading this oasis with contaminants in the form of microbes from Earth, which could destroy Martian lifeforms and their environment. Spacecraft that are sent to touch down on Mars are subjected to careful sterilization procedures to prevent this from happening. But the more gear we send to Mars, the greater the risk.

The most controversial mission that could be envisaged in the near-term would be a sample-return mission. This would aim to return samples of Martian life to Earth. A sample-return mission is realty the only way to perform a proper study of extraterrestrial lifeforms. Despite the increasing sophistication of in-situ explorers like the Curiosity rover (which has no biology experiments), their instruments cannot match the infrastructure of Earth laboratories and personnel. Sample return from Mars would be expensive and complex. It would also generate more opposition than any space mission to date.

Science fiction has regularly painted nightmare scenarios of Earth being invaded by alien life. Usually, it's in the form of intelligent but hostile extraterrestrials that want to attack us. Another scenario involves the recovery of extraterrestrial microbes that are hazardous pathogens, with the potential to cause disease and destroy the ecosystems of our home planet. Astrobiologists frequently brush off the idea of a dangerous organism coming to us from space, but the idea cannot be so easily dismissed.

Tests of the potential hazards posed by Martian life will probably be performed by robot explorers on the planet itself before a sample-return mission is planned. This will involve testing the potential of such life to interact with the biochemistry and cellular structures of Earth organisms.

The usual story goes that a Martian lifeform that is too different from Earth life will lack the compatibility to infect us, but a Martian lifeform similar to Earth life will not be able to challenge our well-trained immune systems and other biological defenses. Such arguments are interesting but lack the rigorous proof that most people and governments would demand.

A sample-return mission from Mars will require extremely reliable systems to return to Earth without releasing the samples into the environment. Special laboratories for the handling of the samples will need to be built, to ensure that the samples remain isolated.

A sample-return mission would attract tremendous opposition and even invite terrorist activity to prevent it. The risks posed by angry humans could be stronger than any threats from Martian organisms!

Finally, there is the question of sending astronauts to Mars. Getting a human spaceflight mission to Mars has been the dream of space enthusiasts since the space age began. Like the discovery of life on Mars, placing human footprints on the planet still seems to be an elusive goal at the present. The discovery of life on Mars would probably make this difficult task even more challenging.

The quarantine implications of sending humans to Mars would be astounding. It is possible that humans and their gear could be confined to the presumably barren surface of the planet, leaving the deeper parts of Mars untouched. But there could still be lingering contamination that, over time, could adapt and migrate. Keeping a human spacecraft free of microbes is unrealistic, short of killing everything inside.

Then there's the question of returning those astronauts to Earth. How long would they be required to stay in quarantine? What happens to them if they are not given a clean bill of health?

Some boffins also dream of the day when humans will not only explore Mars but colonize the planet. This article won't explore the challenges posed by such a task, but will note that colonization is even more controversial than simply landing a few astronauts there.

Would we be willing to risk the destruction of the Martian biosphere to make this happen? Granted, humans have tipped the balance in their favor throughout history in the colonization of different regions of the Earth. Some advocates of Mars colonization suggest that a human colony of Mars could allow the human race to survive a catastrophe on Earth. Is this realistic?

The discovery of life on Mars would answer some huge questions that have captivated scientists, visionaries, and just about everyone who thinks about the greater questions of our existence. It would then raise some more questions as we ponder our response.

Dr Morris Jones is an Australian space analyst and regular contributor to SpaceDaily.com. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email.