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In Depth

Space

The Phoenix mission

A Martian probe will look high and low for signs of water

May 26, 2008

Phoenix mission Illustration of the Phoenix lander (NASA Jet Propulsion Laboratory, University of Arizona)

For the past three years, two Mars rovers have travelled the planet taking measurements and sending data back to Earth. But while the rovers have skimmed the planet's surface, a polar space probe that touched down on Mars on May 25 is designed to dig a little deeper.

Scientists hope the Phoenix Mars lander, armed with a host of scientific tools including a Canadian-built weather station, can help unravel a number of mysteries now that it has arrived after a 10-month, 640-million-kilometre journey.

Among the larger mysteries surrounding Mars are whether the planet was ever capable of sustaining life, and whether it still might hold liquid water beneath its surface.

The Phoenix mission, headed by the NASA Jet Propulsion Laboratory and including contributions from the Canadian Space Agency, hopes to take a step towards answering these questions by examining both the soil and the atmosphere at a landing site in the planet's northern arctic plain.

Canadian Space Agency scientist Victoria Hipkin said the search for liquid water remains the prime focus of our interest in Mars, in part because geological evidence collected from past missions suggest the Red Planet might once have held rivers and possibly oceans of water.

"In its past it looks as if Mars had rivers running on it. There are ancient river beds we've seen from the orbit of Mars," Hipkin told CBC News.

"So there's a big scientific question about Mars and Earth evolving in a very similar way at the beginning when they originated in the solar system, and then having diverged."

The mission

The Phoenix mission has two stated goals: to study the history of water in the Martian arctic and to search for evidence of the potential to support life in the region.

The mission has already achieved at least one major milestone: arriving safely on Mars.

Since the 1970s, European and U.S.-built rockets have sent probes to the planet, but more often than not, the probes have failed before they could land on Mars.

Phoenix's landing was no easy task: the probe had to descend from an initial speed of 20,000 kilometres per hour to just 8 km/h at touchdown. The probe first deployed a parachute as it entered the atmosphere to get from supersonic to subsonic speeds of about 190 km/h, and it used propulsive engines to guide the final descent at a manageable speed for touchdown.

The lander's tools include a robotic arm designed to dig trenches, scoop up soil and water ice samples and deliver these samples to two on-board chemical and geological analyzers. The arm, which also comes equipped with a camera, is the primary instrument for analyzing the planet's surface.

Phoenix mission The Canadian lidar instrument in operation. (NASA Jet Propulsion Laboratory, University of Arizona)

Canada's contribution

The Meteorological Station, or MET, is Canada's contribution to the scientific study of the planet. While the robotic arm probes the planet's surface, the MET offers scientists a chance to better our understanding of the Martian climate and its planetary water cycle.

The Canadian Space Agency and a research team headed by York University — and including contributions from the University of Alberta, Dalhousie University, Optech and the Geological Survey of Canada — will oversee the science operations of the station.

Built by Canadarm maker MacDonald Dettwiler and Associates Ltd. (MDA) of Richmond, B.C., the station consists of two components: a weather mast and an instrument that sends pulses of light to view the atmosphere in a manner similar to radar or sonar.

The weather mast is similar to those found in Earth: it will provide basic information about both the temperature and atmospheric conditions on the planet. It's the first time any probe has landed near the northern polar cap, so the results the weather mast sends back will provide new insight on the region.

We already know, however, that Mars bears little resemblance to Earth, with temperatures getting as cold as -111 C and an atmosphere made up mostly of carbon dioxide that is some 100 times thinner than Earth's.

But unlike Earth, where carbon dioxide plays a key role in the greenhouse effect, the process by which heat is trapped on the planet, the Martian climate appears to be far more influenced by atmospheric dust, kicked into the atmosphere by swirling windstorms.

Laser radar

The MET's other instrument should provide some insight into those dust storms, said Dalhousie University's Tom Duck, one of the scientific team monitoring the probe's findings.

The instrument, called Lidar — or laser radar — sends pulses of green visible light and infrared red into the atmosphere to better understand the composition and movement of particles in the atmosphere.

"If you think with sonar, you're out in your submarine and you send out a ping of sound and you listen for echoes from other boats and the delay time tells you how far away those boats are," Duck told CBC News. "With the Lidar system on the other hand we send up into the atmosphere very short pulses of laser light and watch for the reflection of those pulses of light as they come back and the delay time tells you the distance of whatever you're probing, whether it's clouds or particulate matter in the atmosphere or even molecules."

The readings the weather mast and lidar bring back could help scientists better understand the water cycle of the planet, said Hipkin. That's why the timing of the probe's arrival on the planet is particularly important, she says.

"It's a time when the north polar cap — which is ice — evaporates and sends water vapour down south with the Martian winds, so we expect clouds to form at the latitude of the probe, at about 70 degrees north," she said.

Finding out what these clouds are made of could provide a clue as to what happens to water on the planet, and may point to the presence of liquid water, which because of its unique properties as a facilitator of chemical interactions is seen as a key prerequisite for supporting life.

"We're interested in digging under the soil and seeing if water is there, but we're also interested in seeing if there is surface fog and clouds up there at the same time," said Duck.

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