Red dawn

Mars used to look like cottage country. This year, we may find out what turned it into a barren wasteland.

by Kate Lunau

PL-Caltech/NASA

Mars today is a freeze-dried and rusted desert. But this year, a picture of a very different Mars began to emerge: Four billion years ago, scientists believe, Mars had a thicker atmosphere, a warmer climate and liquid water on the surface. A NASA video illustration, released in November, dramatically illustrates this “lost Mars.” With its blue skies, fat white clouds and sprawling lakes, it could almost be Muskoka cottage country, minus the maple and cedar trees.

In the coming year, we’ll learn more about what caused our neighbouring planet to transform from a place that might have supported life to the barren wasteland it appears to be today. NASA’s Curiosity rover, a minivan-sized explorer that touched down in August 2012, is chugging toward Mount Sharp, the mission’s main target, a 5.5-kilometre-high mound of sedimentary rock that’s expected to offer a scientific smorgasbord. It will arrive in mid-2014. Meanwhile, NASA’s MAVEN mission, which is designed to study how Mars lost its atmosphere, is zooming toward its destination now. When the MAVEN orbiter arrives in Martian orbit in September, it will study how Mars lost its atmosphere, which prompted dramatic climate change. Both of these missions will inform the search for life on the red planet. It turns out it wasn’t always quite so red; long ago, it was grey and blue.

On Dec. 9, scientists working on Curiosity published six papers in the journal Science. One details an ancient Martian lake where life could have thrived long ago, the first habitable environment we know of on a planet other than Earth. Shortly after landing in Gale Crater, the rover’s technicians steered it away from Mount Sharp to explore another intriguing target: a five-metre-deep trough called Yellowknife Bay. (The feature is named for the Northwest Territories capital, where some of the Earth’s oldest rocks have been found.) There, they found evidence of an ancient lake. Mars is red because of the iron oxide on its surface, but when Curiosity drilled down, the mudstone was grey. This environment had all the ingredients necessary to support a type of microbe that breaks down rocks and minerals for energy. While they predict that the environment lasted hundreds to tens of thousands of years, we still don’t know if life took hold there.

John Grotzinger, Curiosity’s chief scientist and lead author of this study, compares it to another recent discovery closer to home. In May, a team of Canadian and British scientists announced they’d found water flowing out of a mine 2.4 kilometres underground, in Timmins, Ont., which had been trapped there for as much as a billion years—with components that could be as old as 2.64 billion years, the age of the rock itself. This ancient water is “full of the kinds of energy that can support life,” says geologist Barbara Sherwood Lollar of the University of Toronto, co-leader of the team. She and others are now trying to determine whether this ancient water does indeed harbour some form of microbe. Grotzinger is watching closely. “If there are micro-organisms down there, they’d be living in exactly the same kind of environment that would have been on Mars,” he says.

Whatever caused Mars to turn into a barren wasteland remains a mystery, although it seems that, after the planet’s magnetic field shut off some 4.1 billion years ago, its atmosphere was shredded by solar wind, says Dave Brain, an assistant professor at the University of Colorado at Boulder in the Laboratory for Atmospheric and Space sciences, and co-investigator on MAVEN. (India’s first Mars orbiter, Mangalyaan, will also be carrying out experiments to study the planet’s atmosphere; it’s expected to arrive two days after MAVEN.) The MAVEN orbiter will be collaborating with Curiosity on the ground as it flies by overhead. “Their instruments will simultaneously measure the atmosphere from the bottom and top,” Brain says.

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In one of the biggest surprises to come from the Curiosity mission, on Dec. 9, scientists announced they’d discovered a way to use the rover’s on-board tools to date rocks on the Martian surface—an ability its designers didn’t plan on when they built it. Scientists determine the approximate age of the surface of bodies in our solar system, including Mars, by counting craters: The more banged-up a surface is, the longer it’s been exposed to impacts from space, including those from asteroids and comets. On Earth, we can get a much more precise number by using what we know about the product of radioactive decay (what’s called radiometric, or isotopic, dating). But until now, taking such a measurement on another planet hasn’t been possible. Incredibly, Curiosity’s investigators figured out how to combine several on-board instruments to date a rock on Mars in this way. “This has never been done before on another planet,” Grotzinger says.

The process works by measuring the ratio of potassium to argon in a rock to figure out how old it is. Using three of Curiosity’s instruments, including the Canadian-built APXS spectrometer, they dated a piece of mudstone found on the floor of Gale Crater, pegging it at about 4.2 billion years. “Let’s say we find a vein with a mineral that contains potassium. We could actually date the time at which water flowed through that crack,” Grotzinger says.

Even more exciting is another set of measurements they took—one that has huge implications in the hunt for organics on Mars, which will help us understand whether the planet ever did host life. Without a magnetic field for protection, Mars is pummelled by galactic cosmic rays, which “destroy organic matter,” says Ken Farley, a professor of geochemistry at the California Institute of Technology and lead investigator of the study. Astrobiologists believe we’d have to dig a few metres into the planet—an incredibly complicated endeavour—to turn up samples of organics that haven’t been cooked by radiation.

Farley’s team developed an ingenious way to identify how long a rock has actually been at the surface of the planet. As they measured the potassium-argon ratio to get the rock’s age, they were also able to detect other noble gases, those produced by interaction with galactic cosmic rays. It turns out that the mudstone they sampled had been at the Martian surface for 80 million years—far less time than they’d expected, which was hundreds of millions, or even a billion. “This can help identify rocks that are young enough to be of interest,” he notes, and will guide Curiosity’s search for organics as it continues exploring.

Sometime next summer, the rover will reach Mount Sharp, inside Gale Crater. “That’s where the pot of gold is expected,” says Ralf Gellert of the University of Guelph, who designed Curiosity’s APXS instrument and is its principal investigator. Mount Sharp tells us “a history of the planet,” he continues, with each layer of rock a separate chapter describing the conditions when it was laid down. Gellert expects Curiosity will learn more about the drastic change Mars went through—the same questions that MAVEN will be probing from above. “We’ll continue the search for habitable environments,” Grotzinger adds, and for organics on Mars. Curiosity will be gathering data while it drives to Mount Sharp, too: Farley’s already got a target in mind that might be of interest, which he expects the rover to reach sometime in January.

In addition to more pure science, we’ll see more of the breathtaking, high-resolution photos Curiosity beams back to Earth next year. “The terrain we’re in right now is very rugged,” Grotzinger says. “We’re driving between low hills, buttes and mesas. When the images start coming down over the next month, people will be oohing and aahing.”

Save the Date // August 2014

MARS SIMULATION

The Mars Society is planning a one-year mission simulation in Canada’s Arctic. Six crew members will live as Martian explorers would: they’ll have to don a spacesuit just to step outside. As on Mars, in Canada’s far North, ‘there’s a real element of isolation and fear,’ says president Robert Zubrin.




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