Will we ever be able to say there is nothing alive on Mars? Will we ever be able to justify future missions to the red planet on some rationale other than the search for extraterrestrials?

Exactly how do we decide when it's time to end the focus on our planetary neighbour and turn our primary exploratory efforts elsewhere?

I ask in part because a casual reader of recent national headlines might have been tempted to pronounce that Canada seems to have aligned with Mars. In August, the Canadian Space Agency and the California Institute of Technology agreed to develop an instrument to help measure methane in the Martian atmosphere.

It will fly on a joint NASA/European Space Agency Mars in 2016.

Then in September, word came out that Canada would be building one of those little roving robots that have scurried around the red planet’s surface in the past.

Why go to Mars and not somewhere else when humanity makes its first interplanetary journey?

The current plans sure aren't the fulfilment of the vision of Marc Garneau, Canada’s first astronaut. In 2004 when he was head of the CSA, he talked about a "distinctly Canadian" trip to Mars that would be as natural an enterprise to us as "building a railway across a vast and rugged country was in 1885."

Contrary to Garneau's vision, we aren’t leading anything these days. We are, as almost always when it comes to space exploration, hitchhikers on others’ missions.

Rather, the reason we are going can be found in the news headlines describing the first mission. "Winnipeg Scientist Helps Probe Mars for Life," said CBCNews.ca. "Canadians Part of the Hunt for Life on Mars," said the Globe and Mail.

Looking for life in all the wrong places?

This interpretation is not just media blather or the fallout of all those little-green-men-on-Mars science fiction stories.

"All the Mars science is couched around the search for life, even if it isn’t explicitly stated," says Jack McConnell of York University, who is one of the scientists behind the effort.

For example, there was debate between NASA and ESA scientists about what instrument to send on the mission. Some favoured one that measured winds, another carbon dioxide, but ultimately the methane won out because of its life-on-Mars component, says McConnell.

The MATMOS instrument will try to figure out what created the methane in the Martian atmosphere. Was it the byproduct of a bacterial biology, as is the case for 90 per cent of the methane found in Earth’s atmosphere? Or did it come from some geological process such as the methane-producing oxidation of iron that happens on Earth?

If it does bear an isotopic signature of a biological source, then it follows there is something alive — probably bacteria — on Mars that is producing it. And if there is life on Mars, it seems almost imperative that humans should travel to there to find out what Martian life might be and what it might do. We will understand our evolution better if we understand their evolution better.

'This quest for life on Mars without having any sense of when that search will be over is not just crazy, it is self-defeating.'

That’s the imperative that the notion of life on Mars engenders, but what if life is absent?

What if the probe says that the weirdness of the methane gas in Mars's atmosphere — it stays up for only about one year and not 300 years as on Earth, and it stays fixed in a few regions and doesn’t travel over the planet’s surface as does atmospheric methane on Earth — is just weird geology?

Can we then say: No life on Mars, time to get on with other reasons for exploration of the solar system?

The answer is anything but clear, because it is not clear what proving there's no life on Mars would involve. McConnell told me, "My feeling is that if we find life, that is one type of answer. But if we don’t, someone will always say, 'You didn’t look here, you didn’t look there, you didn’t look deep enough to find the fossils.'"

He is not alone in this feeling.

"On a practical level, you say you know the possibility of life is so small it is not worth worrying about. But if we go back to the emotional, visceral level, one cellular organization found not on the Earth is to some people a major thing," says James Drummond, Canada Research Chair in Remote Soundings of Atmospheres at Dalhousie University.

All of which creates a profound contradiction. The existence of life on Mars becomes not an objective truth but an article of what you might call a science fiction faith.

Which leads me to the point of this column.

This quest for life on Mars without having any sense of when that search will be over is not just crazy, it is self-defeating. If every time we go to Mars we fail to find the life we so desperately are looking for, it seems the entire effort — whatever else it learned about the planet —  was in vain. And I would venture to say that these never-ending failures also colour our feelings about the virtues of the exploration of the solar system in general.

Everything starts to feel like a failure.

Therefore, I think we should — the Canadian Space Agency and others being the "we" here — come up with a guideline. A "found life" will speak for itself, but life that is absent needs a measure.

That measure should say that if these conditions aren’t met, if the methane on Mars isn’t biological, if nothing biological has been found on the Martian surface after so many missions, then we’re going to stop promoting Mars exploration as the search for life.

Space zealots can believe what they want, but the governments to whom we pay taxes should link future Mars missions, and indeed solar explorations in general, to uncovering things we have some sense are going to be there.

And if there is nothing in that reality which actually inspires us enough to justify the cost of Martian exploration, then so be it.

If the search for life means jumping over visiting the nine-planet barrenness around us and devoting our attention to some Earth-like planet we find circling a nearby star, then so be it.

If we have to grow up when it comes to space exploration, then so be it.