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photographed by the lander cameras and used to determine wind speeds.Humidity is be measured by the Thermal and ElectroConductivity Probe.A key part of the MET is a lidar (light detection and ranging) that will gather dataon atmospheric dust and ice particles. Lidar operates on the same principle asradar, but sends out pulses of laser light instead of radio waves. The light isreflected off the particles and, by measuring the return time and intensity,scientists can determine their location and number.The pioneering work in the development of lidar systems by York Universityscientist Allan Carswell was a major factor that led to Canadian participation inPhoenix. Several years ago, Carswell’s company, Optech Inc. of Toronto,provided a lidar for a study of dust devils in Arizona. The lidar on board Phoenix,built by MDA and Optech, is the first lidar to operate on the surface of anotherplanet.Ice clouds and dustThe lidar will detect the presence of dust, fog and ice clouds in the loweratmosphere. Clouds help to spread water around the planet’s atmosphere andsend it down to the surface. Understanding cloud formation and evolution and themovement of constituents of the lower atmosphere are central to understandingthe water cycle and potential for life. Taylor said the lidar should be able to detectwater-ice clouds that are “reasonably close to the surface”—up to about 20kilometres high.Measuring dust particles is also important to understanding Mars’ weather andclimate because they influence the flow of solar energy within the atmosphereand play an important role in forming clouds. On Mars, dust can be whipped upby the winds into anything from small, localized “dust devils” to long-lived stormsthat cover large regions of the planet.These storms are a potential hazard to future human exploration missions andcan also affect the performance of unmanned vehicles, which often depend onsolar energy for power. “If you get a lot of dust in the atmosphere, that cuts downthe amount of solar radiation reaching the surface, so you can’t charge up yourbatteries during the day,” Taylor said.The lidar’s ability to detect dust will help scientists gain a better understanding ofthe boundary layer on Mars. This is a region just above the surface where mostturbulence occurs and where heat, dust, water vapour and other gases are mixedand transferred between the atmosphere and the surface. Taylor said the52
oundary layer on Mars is generally higher than on Earth—perhaps four to fivekilometres during the day in the Arctic because of solar heating, and less at night.“We think the lidar will be able to tell us is how deep the boundary layer is,” hesaid. “We’re hoping it will detect a horizon—a change in the dust concentration atlevels corresponding to the top of the boundary layer.” This will depend on thesize of the dust particles. If they are large enough to settle out of the atmospheresufficiently rapidly at night, scientists will see the top of the boundary layer.Unfortunately, some Martian dust is very fine and, once stirred up, settles veryslowly, if at all.The MET science team is interpreting the data collected on the planet by usingcomputer models similar to those used for weather forecasting and climateprediction on Earth to analyze the atmospheric chemistry of Mars and the roleplayed by dust.Preparing for the missionLong before landing, while MDA was building the instruments, the Canadianscientific team conducted studies and tests to prepare for the research programduring spacecraft operations. The York team, for example, tested components ofthe temperature sensor taken from the same manufacturing batch as thosedestined for the spacecraft and also built and tested a lidar technically similar tothat destined for Mars.Taylor and his students participated in an investigation that prompted a designchange in the instrument used to collect sub-surface ice samples. From hisprevious research on blowing snow, Taylor knew that when snow is blownaround, it sublimates—changes from a solid to a vapour. He began to wonder ifthis would happen to the ice dug up with a fork-like device on the end of therobotic arm on Phoenix—a laborious process that would take several hours.“It seemed to us that scraping these little chips of ice up and delivering them tothe analysis instrument several hours later could be a problem. We thought theseice chips would sublimate. If it takes them several hours to collect a large enoughsample, they’ll never be able to do it because the sample will vaporize.” His initialcalculations suggested that, at a temperature of –30 degrees Celsius, the chipswould last only half an hour.This theory was greeted with some skepticism so Taylor had a student who wasworking in the Canadian Arctic do some experiments up there. He and someother students also conducted experiments in a chamber at York that simulatesMartian conditions. “We found that if the temperature stays below about –4053
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