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The next U.S. spacecraft to Mars will take along Canadian-built instruments that will provide the first daily weather measurements from the surface of another planet.

The spacecraft, named Phoenix, is supposed to touch down in the northern polar region of the Red Planet early next year.

"We will be able to measure temperature, pressure, wind and the composition of the clouds on Mars," said Stéphane Desjardins, acting director for exploration projects at the Canadian Space Agency, which is footing the $37-million bill for the extraterrestrial weather station.

The lander should provide invaluable information for scientists planning human missions to Mars, where the temperature can swing from a balmy few degrees above zero to a heart-stopping -100.

Mr. Desjardins said the mission, the CSA's first significant contribution to Mars exploration, is a perfect fit for Canada's scientific community. After all, he said, Canadians know an awful lot about polar environments and cold weather.

This week, the Phoenix lander, along with its Canadian components, will be delivered to the Kennedy Space Center in Florida for final preparations before launch. It is set to blast off in early August and will take 10 months to reach the fourth planet from the sun. If everything goes according to plan, it will make a soft landing in late May of 2008.

In addition to its weather station, Phoenix comes equipped with a two-metre-long robotic arm that can dig into the Martian arctic soil, which is believed to resemble the permafrost found in Canada's far north.

Observations from orbiting probes suggest that vast stores of frozen water lie just below the surface in the frigid polar region. If that's the case, Phoenix could be the first spacecraft to physically analyze Martian water, a key ingredient of life and a necessary requirement for human colonization.

"We are hoping we are going to find a mixture of dirt and frozen water," said Karen McBride, who is managing the mission for the U.S. National Aeronautics and Space Administration in Washington, D.C.

"We don't want solid ice because it would be very hard to handle," she said, noting that Arctic ice can be as hard as concrete.

Mini-labs aboard the lander will analyze samples scooped up by the robotic arm, which might be able to dig a trench up to a half-metre deep. Earlier Martian probes barely scratched the surface. Tests will check for organic chemicals and other signs that could reveal whether the site is capable of supporting life.

It's hoped the lander will continue operating for 150 days, or roughly the summer and fall months in northern latitudes. As winter approaches and the sun goes lower in the sky, the solar panels won't be able to generate sufficient power to keep the craft working.

Phoenix is the first in a series of relatively low-cost "scout" missions that are preparing the way for future human landings.

The main body of the spacecraft was cobbled together from the spare or unused parts of two previous ill-fated missions: the Mars Polar Lander, which crashed on the planet in 1999, and the Mars Surveyor, which was mothballed in 2001 after a spate of Mars mission failures.

Like its mythological namesake, Phoenix is literally rising from the ashes of its predecessors, Ms. McBride noted.

Along with cutting costs, using spare parts saved time for the U.S. scientists and technicians assembling the born-again probe. The compressed schedule, however, was a huge disadvantage for the Canadian scientists offering to create new weather instruments for the U.S. spacecraft.

"We had to design and build a lot of it from scratch," said Jim Whiteway, the lead Canadian scientist and an associate professor at York University in Toronto.

He said there were times when the Canadians weren't sure they would meet the deadline.

The biggest challenge was the lidar, an instrument that analyzes clouds and dust in the atmosphere. Similar to radar, it emits a short laser pulse into the sky and then measures the light that bounces back after hitting dust and cloud particles.

Canadian scientists have a long tradition of assembling these sophisticated instruments. However, for this mission, the equipment had to be compact, lightweight and energy efficient while still sturdy enough to operate in the hostile Martian environment.

MDA, the Brampton, Ont., company famed for constructing the Canadarm on the space shuttle, won the contract to build the unique device.

The prototype, about the size of a shoebox and weighing about 10 kilograms, was put through a series of tests in Ottawa labs that can mimic the low atmospheric pressure and frigid conditions of Mars.

The initial tests did not go well as the lidar encountered one glitch after another. The laser was misbehaving and the internal components twisted and broke under the strain of the huge temperature variations. Eventually, the Canadian scientists got everything working.

"These problems happen with any new system," Prof. Whiteway explained. "It was only a matter of time before we found solutions. But with a Mars mission, you don't have the option or the luxury of delay."

The launch date is determined by when Earth and Mars are relatively close to each other. And that happens only once every two years.

The scientific payload

Specialized scientific instruments are supplied by a wide range of institutions, including the Jet Propulsion Laboratory in California, University of Arizona, Max Planck Institute in Germany, University of Neuchatel in Switzerland as well as the Canadian Space Agency.

METEOROLOGICAL STATION The Canadian-built weather station will measure the temperature, pressure and wind on the surface. It will also analyze dust and clouds in the atmosphere. ROBOTIC ARM A robotic arm will dig through the soil to the water ice layer and brings the samples to the craft for analysis.

ROBOTIC ARM CAMERA A camera attached to the arm will take close-up, full colour images of the soil samples.

MICROSCOPY, ELECTROCHEMISTRY AND CONDUCTIVITY ANALYZER By mixing small amounts of Martian soil with water from Earth, these instruments can determine important chemical properties such as acidity and saltiness. A microscope will also examine the soil .

SURFACE STEREOSCOPIC IMAGER This camera will provide high-resolution stereoscopic panoramic images of the surrounding Martian arctic landscape as seen from the landing site.

THERMAL AND EVOLVED GAS ANALYZER Eight tiny ovens will heat the soil and ice samples and then analyze the resulting gases for their chemical composition.

MARS DESCENT IMAGER This camera will take a series of images of the landing site as the craft descends to the surface.

Source: National Aeronautics and Space Administration.

The mission

Despite the success of Mars Pathfinder and the Mars Exploration Rovers, the Phoenix mission will use a lander because it is a different type of

mission. The rovers were designed to study rocks at various locations on the surface of Mars, hunting for evidence that liquid water once flowed there. The Phoenix lander, however, knows exactly where to go to find water. It is going to an area of Mars where water is believed to exist in the form of ice just below the planet's surface; to reach it, however, the spacecraft must dig below the surface.

Phoenix's three key questions: 1. Can the Martian arctic support life?

2. What is the history of water at the landing site?

3. How is the overall Martian climate affected by what happens at the poles?

ON MARS Phoenix will open its solar arrays that provide power for the scientific instruments.

DEVELOPMENT Assembly of the spacecraft began in early 2006 at Lockheed Martin Space Systems in Littleton, Colo., where it was shaken, baked, frozen, zapped and asphyxiated to see if it could survive the extreme conditions of Mars.

LAUNCH This week, Phoenix will be delivered to the Kennedy Space Center at Cape Canaveral, Fla. It will undergo final testing and be loaded aboard a rocket. The 22-day "launch window" - when Earth and Mars are properly aligned for the mission - begins in early August.

CRUISE During the spacecraft's 10-month cruise to Mars, up to six trajectory correction manoeuvres are planned to keep Phoenix on track. Solar panels, which provide power during the journey, will be jettisoned five minutes before entering the thin Martian atmosphere.

LANDING At 125 kilometres above the surface, Phoenix will enter the Martian atmosphere. A heat shield will protect the lander from the extreme temperatures generated by the friction of high-speed entry. A parachute and landing thrusters will also be used to further slow down the descent. The craft will make a soft landing on its three legs.

Images and source: National Aeronautics And Space Administration

Canada's Arctic connection

Does it snow on Mars?

Astronomers have long observed that the Red Planet has polar ice caps that expand and contract with the seasons.

And more recently, orbiting spacecraft have provided evidence that these caps are likely composed of both water ice and frozen carbon dioxide.

Scientists also know that the atmospheric pressure on Mars is too low for liquid water to exist. It simply goes from a solid to a gas in one single step, without the liquid stage in between.

But how do the water vapour and carbon dioxide in the atmosphere end up on the ground to form the polar caps during winter seasons? Does it just instantly appear on the surface, literally growing from the ground up? Or might it drift down from the sky in the form of snow?

Some scientists think an answer might be found in the Canadian Arctic, where extremely cold, dry weather patterns could mimic conditions on Mars.

"In the Arctic, we observe a phenomenon known as diamond dust in which single ice crystals just settle out of the atmosphere," said Jim Whiteway, the lead Canadian scientist on the Phoenix mission to Mars. "It just seems to fall out of thin air. You can still see the stars when it is coming down."

(In southern Canada, where the air tends to contain a lot more moisture than in the Far North, snowflakes are much bigger because they are composed of many ice crystals.)

So, could "diamond dust" help explain how the northern polar cap quickly grows by up to two metres in height each winter season?

Prof. Whiteway said scientists can only speculate. And unfortunately, Phoenix, with its Canadian-built weather station, is unlikely to answer the riddle. That's because the solar-powered lander will probably cease functioning before the long, dark Martian winter season settles in and Phoenix is buried beneath the expanding polar ice cap.

Paul Taylor