Looking for life: Water’s allure becomes an otherworldly quest

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Part of Liquid State, an occasional series on our relationship with water.

Water was all around when John Moores was growing up in Newfoundland. It was part of the scenery and part of his identity. These days, water is still a big part of his life. The difference is that Dr. Moores now spends much of his time thinking about water that is millions of kilometres from home.

An assistant professor of space engineering at York University, Dr. Moores is a participating scientist with the Mars Science Laboratory, the $2.5-billion (U.S.) project that deposited NASA's Curiosity rover into a Martian crater last summer and is yielding new insights into what once transpired there.

"Water is a big part of it," Dr. Moores said in an interview with The Globe and Mail. "We really want to understand what the water story of Mars is: how it changed from being a warm and wet planet in the past to being the arid planet it is today, and whether or not it periodically comes back to life."

The motivation is as big as it gets in science. Of all the questions humans have sought to answer about the cosmos, none are as potent as: "Are we alone?" After more than half a century of exploring the solar system, we still do not know if life, as a phenomenon, is unique to Earth, and what that implies about our chances of finding other civilizations some day among the stars.

For Curiosity – which landed a year ago on August 5 – the road to ET is a wet one.

In recent weeks, Curiosity's explorations have literally shifted into high gear as it begins a series of long drives toward a mysterious mountain that promises the most complete record yet of the planet's aqueous history.

Here on Earth, water is essential to biology. It is the universal solvent that, billions of years ago, allowed the chemical building blocks of life to interact and somehow assemble themselves into the first self-sustaining organisms. Ever since, evolution has driven life into a dizzying array of new and surprising forms – infinitely diverse, but inevitably dependent on water.

Scientists have known for years that there is water on Mars too, albeit mostly frozen solid at the poles or locked in subsurface permafrost. But there is also ample evidence that water flowed freely on Mars billions of years ago, raising the possibility that life may have once gained a foothold there.

Dr. Moores already has his own history with water on the red planet. While working on the Phoenix mission, which landed on the planet's northern plain five years ago, he was among the first to detect fog on Mars – a fitting claim to fame for someone who hails from St. John's.

These days, his work with Curiosity involves tracking the movement of water vapour through the thin Martian atmosphere in response to seasonal changes. With spring having just arrived at the rover's location in Gale Crater on July 31, Dr. Moores expects to see more evidence of water overhead.

"It does start to pick up now that we're moving into warmer temperatures in the Northern Hemisphere," he said. For the rover, that still means daytime highs are below zero C, but as the Martian north pole is increasingly exposed to sunlight, the frozen water there evaporates directly into the atmosphere and forms clouds that migrate around the planet.

Getting a handle on this movement of water is important because water in the atmosphere interacts chemically with surface rocks and can skew measurements designed to reveal the much more ancient history of water – and potentially life – on Mars. Day by day, Dr. Moores and his colleagues watch how minute quantities of water are moving around in the Martian atmosphere, and in doing so help to decode a bigger story.

Ralf Gellert, a physicist at the University of Guelph, is working that story from the other side. He leads the rover's alpha-particle-X-ray spectrometer (APXS), a device that measures the elemental composition of Martian rocks and can help identify minerals that formed in the presence of water billions of years ago.

As the creator of two similar instruments that landed with the Spirit and Opportunity rovers when they touched down in 2004, Dr. Gellert has spent nearly a decade absorbed in the daily business of exploring Mars in more than one location at a time.

What Curiosity has added to the picture has been "amazing," Dr. Gellert said, with the new results clearly showing Mars was once far more habitable than it is today. While Opportunity found places where Mars was once likely covered with evaporating lakes of acidic water, Curiosity has tapped into an even older geologic era, perhaps 3.7 billion years ago, when at least some of the water on Mars was more like freshwater found on Earth today.

This revelation, unveiled in March, has boosted confidence that future missions may one day detect signs of past life on Mars. In July, a NASA science definition team recommended making this the explicit objective of the next U.S. Mars rover, to be launched in 2020.

Dr. Gellert agrees that the possibility that life emerged on Mars billions of years ago now "looks very favourable." But he cautions that finding any trace of it will be a major technical challenge. "Even if life got a hold there, what would you expect to see from it today, with all the radiation, all the chemicals around it that could destroy any remnants?"

Now Curiosity's science team is increasingly turning to the question of where traces of past life might be best preserved and protected, Dr. Gellert said. For this reason, signs of ancient water "and the taste of water" – meaning the chemical traces the water left behind – continue to drive the mission forward.

So far, Curiosity has made its biggest discoveries in a location near its landing site, dubbed Yellowknife Bay (a nod to the important role the capital city of the Northwest Territories has played as a home base for many geological expeditions). As it moves toward the centre of Gale Crater, it will begin to climb its dominant feature, the 5.5-kilometre-high mound of sediment called Aeolis Mons, but referred to by the science team as Mount Sharp.

No one is quite sure how a mountain ends up in the middle of a crater, but it's possible the mound was carved out by wind erosion. Orbiting probes have shown the mound is stacked with layers of sulphates, clays and hematite – all water-related minerals – from different periods in the planet's history.

Dr. Gellert was among those in favour of Curiosity taking its time, but he said he's now eager to get his instrument over to the "promised land" of Mount Sharp. Dr. Moores is eager too, but at York University's Planetary Environments and Exploration Lab, he's also hoping to simulate locations in the solar system where liquid water is known to exist right now, not just billions of years in the past.

At the top of the list is Saturn's enigmatic moon Enceladus. With a noonday surface temperature near -200 C, Enceladus would hardly seem a likely water world. Yet it nevertheless sports geysers that jet hundreds of kilometres out into space, as dramatically revealed in images from NASA's Cassini mission.

An analysis published last week in the journal Nature reveals growing evidence that the source of the geysers is an extensive ocean of water hidden below the tiny moon's frozen surface.

Such evidence is significant in light of work done at Lyle Whyte's microbiology lab at McGill University in Montreal. In May, Dr. Whyte and colleagues revealed that they had isolated the coldest living micro-organism on record. Extracted from the permafrost of Ellesmere Island, where it is thought to live in thin veins of briny water, the bacterium was found to be metabolically active down to temperatures of -25 C.

"This is informing us that such microbes can survive and indeed inhabit subzero salty environments," Dr. Whyte said. He added that with Enceladus potentially harbouring such an environment, the moon is a "top target for finding existing microbial life."

More broadly, water will remain at the focus of solar-system exploration over the coming decade and beyond. Next year, the European Space Agency will drop a lander onto a comet – essentially a giant ball of ice – carrying another one of Dr. Gellert's spectrometers. The results may yield clues to the origins of comets and illuminate their role as carriers of primordial water throughout the solar system. And in 2015, NASA's Dawn mission will arrive at the solar system's largest asteroid, Ceres, a body the size of Quebec that is thought to be water-rich.

Even the largest planets, Jupiter and Saturn, which are gaseous and lack a solid surface, cannot be discounted as potential havens for life, because they have water-bearing clouds in their atmospheres. They offer another piece of the water story that Dr. Moores would like to see more thoroughly explored.

"We [have] never taken a photo from inside the atmosphere of a giant planet, or seen up close the water ice clouds that form in there," Dr. Moores said. "I'd just love to see one of those before my career is done."

When water's allure becomes an otherworldly quest, the possibilities are endless.